Chin. Phys. B

Measurement of ²³²Th (n,γ) cross section at the CSNS Back-n facility in the unresolved resonance region from 4 keV to 100 keV

Bing Jiang(姜炳), Jianlong Han(韩建龙), Jie Ren(任杰), Wei Jiang(蒋伟), Xiaohe Wang(王小鹤), Zian Guo(郭子安), Jianglin Zhang(张江林), Jifeng Hu(胡继峰), Jingen Chen(陈金根), Xiangzhou Cai(蔡翔舟), Hongwei Wang(王宏伟), Longxiang Liu(刘龙祥), Xinxiang Li(李鑫祥), Xinrong Hu(胡新荣), and Yue Zhang(张岳)

Chin. Phys. B, 2022, 31 (6): 060101. DOI: 10.1088/1674-1056/ac5394

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The neutron capture cross section of ²³²Th was measured at the neutron time-of-flight facility Back-n of China Spallation Neutron Source (CSNS) for the first time. The measurement was performed with 4 hydrogen-free deuterated benzene C₆D₆ liquid scintillation detectors, in the ES#2 experiment station on the beam line, at a distance of about 76 m from the neutron-production assembly. The total energy detection principle in combination with the pulse height weighting technique (PHWT) was applied to analyze the measured data. Results of the ²³²Th (n,γ) reaction cross section in the unresolved resonance region from 4 keV to 100 keV were obtained, which shows a good agreement with the existing experimental data from EXFOR, as well as with the evaluated data from the ENDF/B-VIII.0 and CENDL-3.1. In addition, the excitation function of ²³²Th (n,γ)²³³Th reaction in the unresolved resonance region was theoretically calculated by using the code TALYS-1.95. By fitting the experimental cross section and theoretical data, the average parameters in the unresolved resonance region were extracted. The datasets are openly available at http://dx.doi.org/10.11922/sciencedb.j00113.00015.

Neutron activation cross section data library

Xiao-Long Huang(黄小龙), Zhi-Gang Ge(葛智刚), Yong-Li Jin(金永利), Hai-Cheng Wu(吴海成), Xi Tao(陶曦),Ji-Min Wang(王记民), Li-Le Liu(刘丽乐), Yue Zhang(张玥), and Xiao-Fei Wu(吴小飞)

Chin. Phys. B, 2022, 31 (6): 060102. DOI: 10.1088/1674-1056/ac657e

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To satisfy the requirements of nuclear reaction cross sections in nuclear engineering applications and nuclear physics studies, the Neutron Activation Cross Section Data Library has been established. 818 target nuclei including unstable target or isomeric target nuclei are considered in this library. The induced neutron energy range region is between 10^-5 eV and 20 MeV. The standard ENDF-6 format is adopted, including general information, reaction cross sections, multiplicities, and so on. The recommended reaction cross sections were obtained using UNF code system and FDRR nuclear model codes or systematic analysis based on available experimental data. The full evaluated dataset containing the evaluated activation cross sections is openly available at http://doi.org/10.57760/sciencedb.j00113.00024.

Data-driven parity-time-symmetric vector rogue wave solutions of multi-component nonlinear Schrödinger equation Suggested by editors

Li-Jun Chang(常莉君), Yi-Fan Mo(莫一凡), Li-Ming Ling(凌黎明), and De-Lu Zeng(曾德炉)

Chin. Phys. B, 2022, 31 (6): 060201. DOI: 10.1088/1674-1056/ac4cc5

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Rogue waves are a class of nonlinear waves with extreme amplitudes, which usually appear suddenly and disappear without any trace. Recently, the parity-time ($\mathcal {PT}$)-symmetric vector rogue waves (RWs) of multi-component nonlinear Schrödinger equation ($n$-NLSE) are usually derived by the methods of integrable systems. In this paper, we utilize the multi-stage physics-informed neural networks (MS-PINNs) algorithm to derive the data-driven $\mathcal {PT}$ symmetric vector RWs solution of coupled NLS system in elliptic and X-shapes domains with nonzero boundary condition. The results of the experiment show that the multi-stage physics-informed neural networks are quite feasible and effective for multi-component nonlinear physical systems in the above domains and boundary conditions.

Ergodic stationary distribution of a stochastic rumor propagation model with general incidence function

Yuhuai Zhang(张宇槐) and Jianjun Zhu(朱建军)

Chin. Phys. B, 2022, 31 (6): 060202. DOI: 10.1088/1674-1056/ac48fa

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In daily lives, when emergencies occur, rumors will spread widely on the internet. However, it is quite difficult for the netizens to distinguish the truth of the information. The main reasons are the uncertainty of netizens' behavior and attitude, which make the transmission rates of these information among social network groups be not fixed. In this paper, we propose a stochastic rumor propagation model with general incidence function. The model can be described by a stochastic differential equation. Applying the Khasminskii method via a suitable construction of Lyapunov function, we first prove the existence of a unique solution for the stochastic model with probability one. Then we show the existence of a unique ergodic stationary distribution of the rumor model, which exhibits the ergodicity. We also provide some numerical simulations to support our theoretical results. The numerical results give us some possible methods to control rumor propagation. Firstly, increasing noise intensity can effectively reduce rumor propagation when $\widehat{\mathcal{R}}$₀>1. That is, after rumors spread widely on social network platforms, government intervention and authoritative media coverage will interfere with netizens' opinions, thus reducing the degree of rumor propagation. Secondly, speed up the rumor refutation, intensify efforts to refute rumors, and improve the scientific quality of netizen (i.e., increase the value of β and decrease the value of α and γ), which can effectively curb the rumor propagation.

Most probable transition paths in eutrophicated lake ecosystem under Gaussian white noise and periodic force

Jinlian Jiang(姜金连), Wei Xu(徐伟), Ping Han(韩平), and Lizhi Niu(牛立志)

Chin. Phys. B, 2022, 31 (6): 060203. DOI: 10.1088/1674-1056/ac5616

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The effects of stochastic perturbations and periodic excitations on the eutrophicated lake ecosystem are explored. Unlike the existing work in detecting early warning signals, this paper presents the most probable transition paths to characterize the regime shifts. The most probable transition paths are obtained by minimizing the Freidlin-Wentzell (FW) action functional and Onsager-Machlup (OM) action functional, respectively. The most probable path shows the movement trend of the lake eutrophication system under noise excitation, and describes the global transition behavior of the system. Under the excitation of Gaussian noise, the results show that the stability of the eutrophic state and the oligotrophic state has different results from two perspectives of potential well and the most probable transition paths. Under the excitation of Gaussian white noise and periodic force, we find that the transition occurs near the nearest distance between the stable periodic solution and the unstable periodic solution.

A mathematical analysis: From memristor to fracmemristor

Wu-Yang Zhu(朱伍洋), Yi-Fei Pu(蒲亦非), Bo Liu(刘博), Bo Yu(余波), and Ji-Liu Zhou(周激流)

Chin. Phys. B, 2022, 31 (6): 060204. DOI: 10.1088/1674-1056/ac615c

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The memristor is also a basic electronic component, just like resistors, capacitors and inductors. It is a nonlinear device with memory characteristics. In 2008, with HP's announcement of the discovery of the TiO₂ memristor, the new memristor system, memory capacitor (memcapacitor) and memory inductor (meminductor) were derived. Fractional-order calculus has the characteristics of non-locality, weak singularity and long term memory which traditional integer-order calculus does not have, and can accurately portray or model real-world problems better than the classic integer-order calculus. In recent years, researchers have extended the modeling method of memristor by fractional calculus, and proposed the fractional-order memristor, but its concept is not unified. This paper reviews the existing memristive elements, including integer-order memristor systems and fractional-order memristor systems. We analyze their similarities and differences, give the derivation process, circuit schematic diagrams, and an outlook on the development direction of fractional-order memristive elements.

Local sum uncertainty relations for angular momentum operators of bipartite permutation symmetric systems

I Reena, H S Karthik, J Prabhu Tej, Sudha, A R Usha Devi, and A K Rajagopal

Chin. Phys. B, 2022, 31 (6): 060301. DOI: 10.1088/1674-1056/ac5fa3

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We show that violation of the variance based local sum uncertainty relation (LSUR) for angular momentum operators of a bipartite system, proposed by Hofmann and Takeuchi [Phys. Rev. A 68 032103 (2003)], reflects entanglement in the equal bipartitions of an N-qubit symmetric state with even qubits. We establish the one-to-one connection with the violation of LSUR with negativity of covariance matrix [Phys. Lett. A 364 203 (2007)] of the two-qubit reduced system of a permutation symmetric N-qubit state.

Constructing the three-qudit unextendible product bases with strong nonlocality Suggested by editors

Bichen Che(车碧琛), Zhao Dou(窦钊), Xiubo Chen(陈秀波), Yu Yang(杨榆), Jian Li(李剑), and Yixian Yang(杨义先)

Chin. Phys. B, 2022, 31 (6): 060302. DOI: 10.1088/1674-1056/ac4a62

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Unextendible product bases (UPBs) are interesting members of a family of orthogonal product bases. Here, we investigate the construction of 3-qudit UPBs with strong nonlocality. First, a UPB set in ${{C}^{3}}\otimes {{C}^{3}}\otimes {{C}^{3}}$ of size 19 is presented based on the shift UPBs. By mapping the system to a Rubik's cube, we provide a general method of constructing UPBs in ${{C}^{d}}\otimes {{C}^{d}}\otimes {{C}^{d}}$ of size ${{\left(d-1 \right)}^{3}}+2d+5$, whose corresponding Rubik's cube is composed of four parts. Second, for the more general case where the dimensions of parties are different, we extend the classical tile structure to the 3-qudit system and propose the tri-tile structure. By means of this structure, a ${{C}^{4}}\otimes {{C}^{4}}\otimes {{C}^{5}}$ system of size 38 is obtained based on a ${{C}^{3}}\otimes {{C}^{3}}\otimes {{C}^{4}}$ system of size 19. Then, we generalize this approach to the ${{C}^{{{d}_{1}}}}\otimes {{C}^{{{d}_{2}}}}\otimes {{C}^{{{d}_{3}}}}$ system which also consists of four parts. Our research provides a positive answer to the open question raised in by Halder et al. [$Phys. Rev. Lett$. 122 040403 (2019)], indicating that there do exist UPBs that can exhibit strong quantum nonlocality without entanglement.

Digraph states and their neural network representations Suggested by editors

Ying Yang(杨莹) and Huaixin Cao(曹怀信)

Chin. Phys. B, 2022, 31 (6): 060303. DOI: 10.1088/1674-1056/ac401d

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With the rapid development of machine learning, artificial neural networks provide a powerful tool to represent or approximate many-body quantum states. It was proved that every graph state can be generated by a neural network. Here, we introduce digraph states and explore their neural network representations (NNRs). Based on some discussions about digraph states and neural network quantum states (NNQSs), we construct explicitly an NNR for any digraph state, implying every digraph state is an NNQS. The obtained results will provide a theoretical foundation for solving the quantum many-body problem with machine learning method whenever the wave-function is known as an unknown digraph state or it can be approximated by digraph states.

Quantum algorithm for neighborhood preserving embedding ^Hot!

Shi-Jie Pan(潘世杰), Lin-Chun Wan(万林春), Hai-Ling Liu(刘海玲), Yu-Sen Wu(吴宇森), Su-Juan Qin(秦素娟), Qiao-Yan Wen(温巧燕), and Fei Gao(高飞)

Chin. Phys. B, 2022, 31 (6): 060304. DOI: 10.1088/1674-1056/ac523a

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Neighborhood preserving embedding (NPE) is an important linear dimensionality reduction technique that aims at preserving the local manifold structure. NPE contains three steps, i.e., finding the nearest neighbors of each data point, constructing the weight matrix, and obtaining the transformation matrix. Liang et al. proposed a variational quantum algorithm (VQA) for NPE [Phys. Rev. A 101 032323 (2020)]. The algorithm consists of three quantum sub-algorithms, corresponding to the three steps of NPE, and was expected to have an exponential speedup on the dimensionality n. However, the algorithm has two disadvantages: (i) It is not known how to efficiently obtain the input of the third sub-algorithm from the output of the second one. (ii) Its complexity cannot be rigorously analyzed because the third sub-algorithm in it is a VQA. In this paper, we propose a complete quantum algorithm for NPE, in which we redesign the three sub-algorithms and give a rigorous complexity analysis. It is shown that our algorithm can achieve a polynomial speedup on the number of data points m and an exponential speedup on the dimensionality n under certain conditions over the classical NPE algorithm, and achieve a significant speedup compared to Liang et al.'s algorithm even without considering the complexity of the VQA.

Vortex chains induced by anisotropic spin-orbit coupling and magnetic field in spin-2 Bose-Einstein condensates

Hao Zhu(朱浩), Shou-Gen Yin(印寿根), and Wu-Ming Liu(刘伍明)

Chin. Phys. B, 2022, 31 (6): 060305. DOI: 10.1088/1674-1056/ac4020

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We investigate the anisotropic spin-orbit coupled spin-2 Bose-Einstein condensates with Ioffe-Pritchard magnetic field. With nonzero magnetic field, anisotropic spin-orbit coupling will introduce several vortices and further generate a vortex chain. Inside the vortex chain, the vortices connect to each other, forming a line along the axis. The physical nature of the vortex chain can be explained by the particle current and the momentum distribution. The vortex number inside the vortex chain can be influenced via varying the magnetic field. Through adjusting the anisotropy of the spin-orbit coupling, the direction of the vortex chain is changed, and the vortex lattice can be triggered. Moreover, accompanied by the variation of the atomic interactions, the density and the momentum distribution of the vortex chain are affected. The realization and the detection of the vortex chain are compatible with current experimental techniques.

Short-wave infrared continuous-variable quantum key distribution over satellite-to-submarine channels

Qingquan Peng(彭清泉), Qin Liao(廖骎), Hai Zhong(钟海), Junkai Hu(胡峻凯), and Ying Guo(郭迎)

Chin. Phys. B, 2022, 31 (6): 060306. DOI: 10.1088/1674-1056/ac490a

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The trans-media transmission of quantum pulse is one of means of free-space transmission which can be applied in continuous-variable quantum key distribution (CVQKD) system. In traditional implementations for atmospheric channels, the 1500-to-1600-nm pulse is regarded as an ideal quantum pulse carrier. However, the underwater transmission of this pulses tends to suffer from severe attenuation, which inevitably deteriorates the security of the whole CVQKD system. In this paper, we propose an alternative scheme for implementations of CVQKD over satellite-to-submarine channels. We estimate the parameters of the trans-media channels, involving atmosphere, sea surface and seawater and find that the short-wave infrared performs well in the above channels. The 450-nm pulse is used for generations of quantum signal carriers to accomplish quantum communications through atmosphere, sea surface and seawater channels. Numerical simulations show that the proposed scheme can achieve the transmission distance of 600 km. In addition, we demonstrate that non-Gaussian operations can further lengthen its maximal transmission distance, which contributes to the establishment of practical global quantum networks.

Efficient quantum private comparison protocol utilizing single photons and rotational encryption

Tian-Yi Kou(寇天翊), Bi-Chen Che(车碧琛), Zhao Dou(窦钊), Xiu-Bo Chen(陈秀波), Yu-Ping Lai(赖裕平), and Jian Li(李剑)

Chin. Phys. B, 2022, 31 (6): 060307. DOI: 10.1088/1674-1056/ac65f0

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As a branch of quantum secure multiparty computation, quantum private comparison is applied frequently in many fields, such as secret elections, private voting, and identification. A quantum private comparison protocol with higher efficiency and easier implementation is proposed in this paper. The private secrets are encoded as single polarized photons and then encrypted with a homomorphic rotational encryption method. Relying on this method and the circular transmission mode, we implement the multiplexing of photons, raising the efficiency of our protocol to 100%. Our protocol is easy to realize since only single photons, unitary operation, and single-particle measurement are introduced. Meanwhile, the analysis shows that our protocol is also correct and secure.

Coherence migration in high-dimensional bipartite systems

Zhi-Yong Ding(丁智勇), Pan-Feng Zhou(周攀峰), Xiao-Gang Fan(范小刚),Cheng-Cheng Liu(刘程程), Juan He(何娟), and Liu Ye(叶柳)

Chin. Phys. B, 2022, 31 (6): 060308. DOI: 10.1088/1674-1056/ac48f8

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The conservation law for first-order coherence and mutual correlation of a bipartite qubit state was firstly proposed by Svozilík et al., and their theories laid the foundation for the study of coherence migration under unitary transformations. In this paper, we generalize the framework of first-order coherence and mutual correlation to an arbitrary (m $\otimes$ n)-dimensional bipartite composite state by introducing an extended Bloch decomposition form of the state. We also generalize two kinds of unitary operators in high-dimensional systems, which can bring about coherence migration and help to obtain the maximum or minimum first-order coherence. Meanwhile, the coherence migration in open quantum systems is investigated. We take depolarizing channels as examples and establish that the reduced first-order coherence of the principal system over time is completely transformed into mutual correlation of the (2 $\otimes$ 4)-dimensional system-environment bipartite composite state. It is expected that our results may provide a valuable idea or method for controlling the quantum resource such as coherence and quantum correlations.

Nonlinear dynamical wave structures of Zoomeron equation for population models

Ahmet Bekir and Emad H M Zahran

Chin. Phys. B, 2022, 31 (6): 060401. DOI: 10.1088/1674-1056/ac48ff

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The nonlinear dynamical exact wave solutions to the non-fractional order and the time-fractional order of the biological population models are achieved for the first time in the framwork of the Paul-Painlevé approach method (PPAM). When the variables appearing in the exact solutions take specific values, the solitary wave solutions will be easily obtained. The realized results prove the efficiency of this technique.

Simulation of crowd dynamics in pedestrian evacuation concerning panic contagion: A cellular automaton approach Suggested by editors

Guan-Ning Wang(王冠宁), Tao Chen(陈涛), Jin-Wei Chen(陈锦炜), Kaifeng Deng(邓凯丰), and Ru-Dong Wang(王汝栋)

Chin. Phys. B, 2022, 31 (6): 060402. DOI: 10.1088/1674-1056/ac4a66

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The study of the panic evacuation process is of great significance to emergency management. Panic not only causes negative emotions such as irritability and anxiety, but also affects the pedestrians decision-making process, thereby inducing the abnormal crowd behavior. Prompted by the epidemiological SIR model, an extended floor field cellular automaton model was proposed to investigate the pedestrian dynamics under the threat of hazard resulting from the panic contagion. In the model, the conception of panic transmission status (PTS) was put forward to describe pedestrians' behavior who could transmit panic emotions to others. The model also indicated the pedestrian movement was governed by the static and hazard threat floor field. Then rules that panic could influence decision-making process were set up based on the floor field theory. The simulation results show that the stronger the pedestrian panic, the more sensitive pedestrians are to hazards, and the less able to rationally find safe exits. However, when the crowd density is high, the panic contagion has a less impact on the evacuation process of pedestrians. It is also found that when the hazard position is closer to the exit, the panic will propagate for a longer time and have a greater impact on the evacuation. The results also suggest that as the extent of pedestrian's familiarity with the environment increases, pedestrians spend less time to escape from the room and are less sensitive to the hazard. In addition, it is essential to point out that, compared with the impact of panic contagion, the pedestrian's familiarity with environment has a more significant influence on the evacuation.

Solutions and memory effect of fractional-order chaotic system: A review

Shaobo He(贺少波), Huihai Wang(王会海), and Kehui Sun(孙克辉)

Chin. Phys. B, 2022, 31 (6): 060501. DOI: 10.1088/1674-1056/ac43ae

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Fractional calculus is a 300 years topic, which has been introduced to real physics systems modeling and engineering applications. In the last few decades, fractional-order nonlinear chaotic systems have been widely investigated. Firstly, the most used methods to solve fractional-order chaotic systems are reviewed. Characteristics and memory effect in those method are summarized. Then we discuss the memory effect in the fractional-order chaotic systems through the fractional-order calculus and numerical solution algorithms. It shows that the integer-order derivative has full memory effect, while the fractional-order derivative has nonideal memory effect due to the kernel function. Memory loss and short memory are discussed. Finally, applications of the fractional-order chaotic systems regarding the memory effects are investigated. The work summarized in this manuscript provides reference value for the applied scientists and engineering community of fractional-order nonlinear chaotic systems.

The dynamics of a memristor-based Rulkov neuron with fractional-order difference

Yan-Mei Lu(卢艳梅), Chun-Hua Wang(王春华), Quan-Li Deng(邓全利), and Cong Xu(徐聪)

Chin. Phys. B, 2022, 31 (6): 060502. DOI: 10.1088/1674-1056/ac539a

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The exploration of the memristor model in the discrete domain is a fascinating hotspot. The electromagnetic induction on neurons has also begun to be simulated by some discrete memristors. However, most of the current investigations are based on the integer-order discrete memristor, and there are relatively few studies on the form of fractional order. In this paper, a new fractional-order discrete memristor model with prominent nonlinearity is constructed based on the Caputo fractional-order difference operator. Furthermore, the dynamical behaviors of the Rulkov neuron under electromagnetic radiation are simulated by introducing the proposed discrete memristor. The integer-order and fractional-order peculiarities of the system are analyzed through the bifurcation graph, the Lyapunov exponential spectrum, and the iterative graph. The results demonstrate that the fractional-order system has more abundant dynamics than the integer one, such as hyper-chaos, multi-stable and transient chaos. In addition, the complexity of the system in the fractional form is evaluated by the means of the spectral entropy complexity algorithm and consequences show that it is affected by the order of the fractional system. The feature of fractional difference lays the foundation for further research and application of the discrete memristor and the neuron map in the future.

The transition from conservative to dissipative flows in class-B laser model with fold-Hopf bifurcation and coexisting attractors

Yue Li(李月), Zengqiang Chen(陈增强), Mingfeng Yuan(袁明峰), and Shijian Cang(仓诗建)

Chin. Phys. B, 2022, 31 (6): 060503. DOI: 10.1088/1674-1056/ac43a2

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Dynamical behaviors of a class-B laser system with dissipative strength are analyzed for a model in which the polarization is adiabatically eliminated. The results show that the injected signal has an important effect on the dynamical behaviors of the system. When the injected signal is zero, the dissipative term of the class-B laser system is balanced with external interference, and the quasi-periodic flows with conservative phase volume appear. And when the injected signal is not zero, the stable state in the system is broken, and the attractors (period, quasi-period, and chaos) with contractive phase volume are generated. The numerical simulation finds that the system has not only one attractor, but also coexisting phenomena (period and period, period and quasi-period) in special cases. When the injected signal passes the critical value, the class-B laser system has a fold-Hopf bifurcation and exists torus "blow-up" phenomenon, which will be proved by theoretical analysis and numerical simulation.

Thermodynamic properties of two-dimensional charged spin-1/2 Fermi gases Suggested by editors

Jia-Ying Yang(杨家营), Xu Liu(刘旭), Ji-Hong Qin(秦吉红), and Huai-Ming Guo(郭怀明)

Chin. Phys. B, 2022, 31 (6): 060504. DOI: 10.1088/1674-1056/ac4e0b

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Based on the mean-field theory, we investigate the thermodynamic properties of the two-dimensional (2D) charged spin-1/2 Fermi gas. Landé factor g is introduced to measure the strength of the paramagnetic effect. There is a competition between diamagnetism and paramagnetism in the system. The larger the Landé factor, the smaller the entropy and specific heat. Diamagnetism tends to increase the entropy, while paramagnetism leads to the decrease of the entropy. We find that there exists a critical value of Landé factor for the transition point due to the competition. The entropy of the system increases with the magnetic field when g < 0.58. With the growth of paramagnetism, when g > 0.58, the entropy first decreases with the magnetic field, then reaches a minimum value, and finally increases again. Both the entropy and specific heat increase with the temperature, and no phase transition occurs. The specific heat tends to a constant value at the hightemperature limit, and it approaches to zero at very low temperatures, which have been proved by the analytical calculation.

Dynamical quantum phase transition in XY chains with the Dzyaloshinskii-Moriya and XZY-YZX three-site interactions

Kaiyuan Cao(曹凯源), Ming Zhong(钟鸣), and Peiqing Tong(童培庆)

Chin. Phys. B, 2022, 31 (6): 060505. DOI: 10.1088/1674-1056/ac4a6e

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We study the dynamical quantum phase transitions (DQPTs) in the $XY$ chains with the Dzyaloshinskii-Moriya interaction and the $XZY$-$YZX$ type of three-site interaction after a sudden quench. Both the models can be mapped to the spinless free fermion models by the Jordan-Wigner and Bogoliubov transformations with the form $H=\sum_{k}ǎrepsilon_{k}(\eta^{†}_{k}\eta_{k}-\frac{1}{2})$, where the quasiparticle excitation spectra $ǎrepsilon_{k}$ may be smaller than 0 for some $k$ and are asymmetrical ($ǎrepsilon_{k}\neqǎrepsilon_{-k}$). It is found that the factors of Loschmidt echo equal 1 for some $k$ corresponding to the quasiparticle excitation spectra of the pre-quench Hamiltonian satisfying $ǎrepsilon_{k}\cdotǎrepsilon_{-k}<0$, when the quench is from the gapless phase. By considering the quench from different ground states, we obtain the conditions for the occurrence of DQPTs for the general $XY$ chains with gapless phase, and find that the DQPTs may not occur in the quench across the quantum phase transitions regardless of whether the quench is from the gapless phase to gapped phase or from the gapped phase to gapless phase. This is different from the DQPTs in the case of quench from the gapped phase to gapped phase, in which the DQPTs will always appear. Moreover, we analyze the different reasons for the absence of DQPTs in the quench from the gapless phase and the gapped phase. The conclusion can also be extended to the general quantum spin chains.

Numerical study of a highly sensitive surface plasmon resonance sensor based on circular-lattice holey fiber

Jian-Fei Liao(廖健飞), Dao-Ming Lu(卢道明), Li-Jun Chen(陈丽军), and Tian-Ye Huang(黄田野)

Chin. Phys. B, 2022, 31 (6): 060701. DOI: 10.1088/1674-1056/ac43a5

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A new design of surface plasmon resonance (SPR) sensor employing circular-lattice holey fiber to achieve high-sensitivity detection is proposed. The sensing performance of the proposed sensor is numerically investigated and the results indicate that our proposed SPR sensor can be applied to the near-mid infrared detection. Moreover, the maximum wavelength sensitivity of our proposed sensor can reach as high as 1.76×10⁴ nm/refractive index unit (RIU) and the maximum wavelength interrogation resolution can be up to 5.68×10^-6 RIU when the refractive index (RI) of analyte lies in (1.31, 1.36). Thanks to its excellent sensing performance, our proposed SPR sensor will have great potential applications for biological analytes detection, food safety control, bio-molecules detection and so on.

In-situ ultrasonic calibrations of pressure and temperature in a hinge-type double-stage cubic large volume press

Qingze Li(李青泽), Xiping Chen(陈喜平), Lei Xie(谢雷), Tiexin Han(韩铁鑫), Jiacheng Sun(孙嘉程), and Leiming Fang(房雷鸣)

Chin. Phys. B, 2022, 31 (6): 060702. DOI: 10.1088/1674-1056/ac4902

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Here, simultaneous in-situ calibration of pressures and temperatures was performed in a hinge-type second-stage cubic large volume press (LVP) up to 15 GPa and 1400 K by an acoustic travel-time approach. Based on the recently reported P-t_S and P-T-t_P-t_S equations for Al₂O₃ buffer rod, the cell pressures and temperatures in the chamber of LVP were in-situ determined, in comparison with those by conventional off-line (or fixed-points) pressure calibration method and direct thermocouple measurement, respectively. It is found that the cell pressures of the LVP chamber are significantly reduced after annealing at simultaneous high pressures and high temperatures, owing to the stress relaxation as accumulate in the LVP chamber. This acoustic travel-time method is verified to be a good way for precise determination of thermal (cell) pressures at high temperature conditions, and is of great importance and necessity to conduct in-situ physical property measurements under extreme high P-T conditions, especially when the precious synchrotron x-ray/neutron diffraction beams are not available.

Synchronous detection of multiple optical characteristics of atmospheric aerosol by coupled photoacoustic cavity

Hua-Wei Jin(靳华伟), Ren-Zhi Hu(胡仁志), Pin-Hua Xie(谢品华), and Ping Luo(罗平)

Chin. Phys. B, 2022, 31 (6): 060703. DOI: 10.1088/1674-1056/ac43ad

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Owing to the influence of sampling loss, cavity difference and detecting source, the multi-optical parameter measurement of atmospheric aerosol cannot be detected simultaneously in the same reference environment. In order to solve this problem, a new method of simultaneously detecting the aerosol optical parameters by coupling cavity ring-down spectrometer with photoacoustic spectroscopy is proposed. Firstly, the coupled photoacoustic cavity is formed by the organic fusion of the photoacoustic cavity and the ring-down cavity. Secondly, the integrated design of the coupling spectroscopy system is carried out. Finally, the extinction coefficient and absorption coefficient of aerosol are measured simultaneously by the system, and then the aerosol scattering coefficient and single albedo are calculated indirectly. The accuracy of the system is verified by comparing with the data from the environmental quality monitoring station, which provides a new idea for the detection of multi-optical characteristics of atmospheric aerosol.

Simulating the resonance-mediated (1+2)-three-photon absorption enhancement in Pr³⁺ ions by a rectangle phase modulation

Wenjing Cheng(程文静), Yuan Li(李媛), Hongzhen Qiao(乔红贞), Meng Wang(王蒙), Shaoshuo Ma(马绍朔), Fangjie Shu(舒方杰), Chuanqi Xie(解传奇), and Guo Liang(梁果)

Chin. Phys. B, 2022, 31 (6): 063201. DOI: 10.1088/1674-1056/ac5398

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Enhancing the upconversion luminescence of rare earth ions is crucial for their applications in the laser sources, fiber optic communications, color displays, biolabeling, and biomedical sensors. In this paper, we theoretically study the resonance-mediated (1+2)-three-photon absorption in Pr³⁺ ions by a rectangle phase modulation. The results show that the resonance-mediated (1+2)-three-photon absorption can be effectively enhanced by properly designing the depth and width of the rectangle phase modulation, which can be attributed to the constructive interference between on-resonant and near-resonant three-photon excitation pathways. Further, the enhancement efficiency of resonance-mediated (1+2)-three-photon absorption can be affected by the pulse width (or spectral bandwidth) of femtosecond laser field, final state transition frequency, and absorption bandwidths. This research can provide a clear physical picture for understanding and controlling the multi-photon absorption in rare-earth ions, and also can provide theoretical guidance for improving the up-conversion luminescence.

Photoelectron momentum distributions of Ne and Xe dimers in counter-rotating circularly polarized laser fields Suggested by editors

Zhi-Xian Lei(雷志仙), Qing-Yun Xu(徐清芸), Zhi-Jie Yang(杨志杰), Yong-Lin He(何永林), and Jing Guo(郭静)

Chin. Phys. B, 2022, 31 (6): 063202. DOI: 10.1088/1674-1056/ac4e05

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The strong-field ionization of dimers is investigated theoretically in counter-rotating circularly polarized laser fields. By numerically solving the two-dimensional (2D) time-dependent Schrödinger equation (TDSE) with the single-electron approximation (SEA) frame, we present the photoelectron momentum distributions (PMDs) and photoelectron angular distribution (PADs) of aligned Ne and Xe dimers. It is found that the PMDs and PADs strongly depend on the time delays by counter-rotating circularly polarized laser pulses. The results can be explained by the ultrafast photoionization model and the evolution of electron wave packets for Ne and Xe dimers. Besides, We make a comparison of PMDs between Ne atom and Ne dimer.

Numerical studies of atomic three-step photoionization processes with non-monochromatic laser fields

Xiao-Yong Lu(卢肖勇), Li-De Wang(王立德), and Yun-Fei Li(李云飞)

Chin. Phys. B, 2022, 31 (6): 063203. DOI: 10.1088/1674-1056/ac490b

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The atomic selective multi-step photoionization process is a critical step in laser isotope separation. In this work, we study three-step photoionization processes with non-monochromatic laser fields theoretically based on the semi-classical theory. Firstly, three bandwidth models, including the chaotic field model, de-correlation model, and phase diffusion model, are introduced into the density matrix equations. The numerical results are compared with each other comprehensively. The phase diffusion model is selected for further simulations in terms of the correspondence degree to physical practice. Subsequently, numerical calculations are carried out to identify the influences of systematic parameters, including laser parameters (Rabi frequency, bandwidth, relative time delay, frequency detuning) and atomic Doppler broadening, on photoionization processes. In order to determine the optimal match among different systematic parameters, the ionization yield of resonant isotope, and selectivity factor are adopted as evaluation indexes to guide the design and optimization process. The results in this work can provide a rewarding reference for laser isotope separation.

Nd L-shell x-ray emission induced by light ions

Xian-Ming Zhou(周贤明), Jing Wei(尉静), Rui Cheng(程锐), Yan-Hong Chen(陈燕红),Ce-Xiang Mei(梅策香), Li-Xia Zeng(曾利霞), Yu Liu(柳钰), Yan-Ning Zhang(张艳宁), Chang-Hui Liang(梁昌慧), Yong-Tao Zhao(赵永涛), and Xiao-An Zhang(张小安)

Chin. Phys. B, 2022, 31 (6): 063204. DOI: 10.1088/1674-1056/ac4488

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The L-shell x-ray of Nd has been obtained for 300-600 keV He²⁺ ions impacting, and compared with that produced by H⁺ and H₂⁺ ions. The threshold of projectile kinetic energy for L-shell ionization of Nd is crudely verified in the energy region of about 300-400 keV. It is found that the energy of the distinct L-subshell x-rays has a blue shift. The relative intensity ratios of Lβ_{1, 3, 4} and Lβ_{2, 15} to Lα_{1, 2} x-ray are enlarged compared to the atomic data, and they decrease with the increase of the incident energy, and increase with increasing the effective nuclear charge of the incident ions. That is interpreted by the multiple ionization of outer-shells induced by light ions.

Collision site effect on the radiation dynamics of cytosine induced by proton Suggested by editors

Xu Wang(王旭), Zhi-Ping Wang(王志萍), Feng-Shou Zhang(张丰收), and Chao-Yi Qian (钱超义)

Chin. Phys. B, 2022, 31 (6): 063401. DOI: 10.1088/1674-1056/ac4900

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By combing the time-dependent density functional calculations for electrons with molecular dynamics simulations for ions (TDDFT-MD) nonadiabatically in real time, we investigate the microscopic mechanism of collisions between cytosine and low-energy protons with incident energy ranging from 150 eV to 1000 eV. To explore the effects of the collision site and the proton incident energy on irradiation processes of cytosine, two collision sites are specially considered, which are N and O both acting as the proton receptors when forming hydrogen bonds with guanine. Not only the energy loss and the scattering angle of the projectile but also the electronic and ionic degrees of freedom of the target are identified. It is found that the energy loss of proton increases linearly with the increase of the incident energy in both situations, which are 14.2% and 21.1% of the incident energy respectively. However, the scattering angles show different behaviors in these two situations when the incident kinetic energy increases. When proton collides with O, the scattering angle of proton is larger and the energy lost is more, while proton captures less electrons from O. The calculated fragment mass distribution shows the high counts of the fragment mass of 1, implying the production of H⁺ fragment ion from cytosine even for proton with the incident energy lower than keV. Furthermore, the calculated results show that N on cytosine is easier to be combined with low-energy protons to form NH bonds than O.

The influence of collision energy on magnetically tuned ⁶Li-⁶Li Feshbach resonance Suggested by editors

Rong Zhang(张蓉), Yong-Chang Han(韩永昌), Shu-Lin Cong(丛书林), and Maksim B Shundalau

Chin. Phys. B, 2022, 31 (6): 063402. DOI: 10.1088/1674-1056/ac4cc3

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The effect of collision energy on the magnetically tuned $^{6}$Li-$^{6}$Li Feshbach resonance (FR) is investigated theoretically by using the coupled-channel (CC) method for the collision energy ranging from 1 μ$ {\rm K} \cdot {k}_{\rm B}$ to 100 μ$ {\rm K} \cdot {k}_{\rm B}$. At the collision energy of 1 μ$ {\rm K} \cdot {k}_{\rm B}$, the resonance positions calculated are 543.152 Gs (s wave, the unit $1 {\rm Gs}=10^{-4} {\rm T}$), 185.109 Gs (p wave $|m_{l}| = 0$), and 185.113 Gs (p wave $|m_{l}| = 1$), respectively. The p-wave FR near 185 Gs exibits a doublet structure of 4 mGs, associated with dipole-dipole interaction. With the increase of the collision energy, it is found that the splitting width remains the same (4 mGs), and that the resonance positions of s and p waves are shifted to higher magnetic fields with the increase of collision energy. The variations of the other quantities including the resonance width and the amplitude of the total scattering section are also discussed in detail. The thermally averaged elastic rate coefficients at $T=10$, 15, 20, 25 K are calculated and compared.

Ion-focused propagation of a relativistic electron beam in the self-generated plasma in atmosphere Suggested by editors

Jian-Hong Hao(郝建红), Bi-Xi Xue(薛碧曦), Qiang Zhao(赵强), Fang Zhang(张芳), Jie-Qing Fan(范杰清), and Zhi-Wei Dong(董志伟)

Chin. Phys. B, 2022, 31 (6): 064101. DOI: 10.1088/1674-1056/ac4a60

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It is known that ion-focused regime (IFR) can effectively suppress expansion of a relativistic electron beam (REB). Using the particle-in-cell Monte Carlo collision (PIC-MCC) method, we numerically investigate the propagation of an REB in neutral gas. The results demonstrate that the beam body is charge neutralization and a stable IFR can be established. As a result, the beam transverse dimensions and longitudinal velocities keep close to the initial parameters. We also calculate the charge and current neutralization factors of the REB. Combined with envelope equations, we obtain the variations of beam envelopes, which agree well with the PIC simulations. However, both the energy loss and instabilities of the REB may lead to a low transport efficiency during long-range propagation. It is proved that decreasing the initial pulse length of the REB can avoid the influence of electron avalanche. Using parts of REB pulses to build a long-distance IFR in advance can improve the beam quality of subsequent pulses. Further, a long-distance IFR may contribute to the implementation of long-range propagation of the REB in space environment.

Influence of optical nonlinearity on combining efficiency in ultrashort pulse fiber laser coherent combining system

Yun-Chen Zhu(朱云晨), Ping-Xue Li(李平雪), Chuan-Fei Yao(姚传飞), Chun-Yong Li(李春勇),Wen-Hao Xiong(熊文豪), and Shun Li(李舜)

Chin. Phys. B, 2022, 31 (6): 064201. DOI: 10.1088/1674-1056/ac448a

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The influence of optical nonlinearity on combining efficiency in ultrashort pulse fiber laser coherent combining system is investigated theoretically and experimentally. In the theoretical work, a new theoretical algorithm is presented for the coherent combining efficiency, which can be used to quantify the spectral coherence decay induced by optical nonlinearity imbalance between the sub-beams. The spectral information of the sub-beam is obtained by numerically solving the nonlinear Schrödinger equation (NLSE) in this algorithm to ensure an accurate prediction. In the experimental work, the coherent combining of two all-fiber picosecond lasers is achieved, and the influence of imbalanced optical nonlinearity on the combining efficiency is studied, which agrees with the theoretical prediction. This paper reveals the physical mechanism for the influence of optical nonlinearity on the combining efficiency, which is valuable for the coherent combining of ultrashort pulse fiber laser beams.

Efficient implementation of x-ray ghost imaging based on a modified compressive sensing algorithm

Haipeng Zhang(张海鹏), Ke Li(李可), Changzhe Zhao(赵昌哲), Jie Tang(汤杰), and Tiqiao Xiao(肖体乔)

Chin. Phys. B, 2022, 31 (6): 064202. DOI: 10.1088/1674-1056/ac48f7

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Towards efficient implementation of x-ray ghost imaging (XGI), efficient data acquisition and fast image reconstruction together with high image quality are preferred. In view of radiation dose resulted from the incident x-rays, fewer measurements with sufficient signal-to-noise ratio (SNR) are always anticipated. Available methods based on linear and compressive sensing algorithms cannot meet all the requirements simultaneously. In this paper, a method based on a modified compressive sensing algorithm with conjugate gradient descent method (CGDGI) is developed to solve the problems encountered in available XGI methods. Simulation and experiments demonstrate the practicability of CGDGI-based method for the efficient implementation of XGI. The image reconstruction time of sub-second implicates that the proposed method has the potential for real-time XGI.

Heralded path-entangled NOON states generation from a reconfigurable photonic chip

Xinyao Yu(于馨瑶), Pingyu Zhu(朱枰谕), Yang Wang(王洋), Miaomiao Yu(余苗苗), Chao Wu(吴超),Shichuan Xue(薛诗川), Qilin Zheng(郑骑林), Yingwen Liu(刘英文), Junjie Wu(吴俊杰), and Ping Xu(徐平)

Chin. Phys. B, 2022, 31 (6): 064203. DOI: 10.1088/1674-1056/ac3501

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Maximal multi-photon entangled states, known as NOON states, play an essential role in quantum metrology. With the number of photons growing, NOON states are becoming increasingly powerful and advantageous for obtaining supersensitive and super-resolved measurements. In this paper, we propose a universal scheme for generating three- and four-photon path-entangled NOON states on a reconfigurable photonic chip via photons subtracted from pairs and detected by heralding counters. Our method is postselection free, enabling phase supersensitive measurements and sensing at the Heisenberg limit. Our NOON-state generator allows for integration of quantum light sources as well as practical and portable precision phase-related measurements.

Sequential generation of self-starting diverse operations in all-fiber laser based on thulium-doped fiber saturable absorber Suggested by editors

Pei Zhang(张沛), Kaharudin Dimyati, Bilal Nizamani, Mustafa M. Najm, and S. W. Harun

Chin. Phys. B, 2022, 31 (6): 064204. DOI: 10.1088/1674-1056/ac3ba9

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Self-starting Q-switching, Q-switched mode-locking and mode-locking operation modes are achieved sequentially in an all-fiber erbium-doped fiber laser with thulium-doped fiber saturable absorber for the first time. The central wavelengths of Q-switching, Q-switched mode-locking and mode-locking operation modes are 1569.7 nm, 1570.9 nm, and 1572 nm, respectively. The mode-locking operation of the proposed fiber laser generates stable dark soliton with a repetition rate of 0.99 MHz and signal-to-noise ratio of 65 dB. The results validate the capability of generating soliton pulse by doped fiber saturable absorber. Furthermore, the proposed fiber laser is beneficial to the applications of optical communication and signal processing system.

Influence of water environment on paint removal and the selection criteria of laser parameters

Li-Jun Zhang(张丽君), Kai-Nan Zhou(周凯南), Guo-Ying Feng(冯国英), Jing-Hua Han(韩敬华),Na Xie(谢娜), and Jing Xiao(肖婧)

Chin. Phys. B, 2022, 31 (6): 064205. DOI: 10.1088/1674-1056/ac539b

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Laser paint removal in a water environment does not diffuse ablation pollution products into air. Characteristics of water, such as high specific heat and heat flux, generate different effects of the laser paint removal than in an air environment. In this study, the effects of air and water environments on the mechanism and effect of laser paint removal are analyzed and compared experimentally and theoretically. In air, thermodynamic ablation causes removal of paint, whereas in water, stress coupled with plasma shock waves cause tear and splash removal of paint layers after fracture and damage. Fracture and pressure thresholds of the paint and substrate, respectively, indicate the optimum energy density range for laser paint removal in water, providing a reference for engineering applications.

Generation of stable and tunable optical frequency linked to a radio frequency by use of a high finesse cavity and its application in absorption spectroscopy

Yueting Zhou(周月婷), Gang Zhao(赵刚), Jianxin Liu(刘建鑫), Xiaojuan Yan(闫晓娟), Zhixin Li(李志新), Weiguang Ma(马维光), and Suotang Jia(贾锁堂)

Chin. Phys. B, 2022, 31 (6): 064206. DOI: 10.1088/1674-1056/ac4905

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The laser frequency could be linked to an radio frequency through an external cavity by the combination of Pound-Drever-Hall and Devoe-Brewer locking techniques. A stable and tunable optical frequency at wavelength of 1.5 μm obtained by a cavity with high finesse of 96000 and a fiber laser has been demonstrated, calibrated by a commercial optical frequency comb. The locking performances have been analyzed by in-loop and out-loop noises, indicating that the absolute frequency instability could be down to 50 kHz over 1 s and keep to less than 110 kHz over 2.5 h. Then, the application of this stabilized laser to the direct absorption spectroscopy has been performed. With the help of balanced detection, the detection sensitivity, in terms of optical density, can reach to 9.4×10^-6.

Tunable enhanced spatial shifts of reflective beam on the surface of a twisted bilayer of hBN

Yu-Bo Li(李宇博), Hao-Yuan Song(宋浩元), Yu-Qi Zhang(张玉琦), Xiang-Guang Wang(王相光),Shu-Fang Fu(付淑芳), and Xuan-Zhang Wang(王选章)

Chin. Phys. B, 2022, 31 (6): 064207. DOI: 10.1088/1674-1056/ac3733

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We investigated Goos-Hänchen (GH) and Imbert-Fedorov (IF) shifts of a reflective beam on a twisted bilayer of hexagonal boron nitride (hBN), where a left circularly polarized beam was incident on the surface. Our results demonstrate that the twist angle between the two optical axes plays an important role in obtaining large shifts with a high reflectivity. The GH shift with 10λ₀ is achieved, while the reflectivity is near 100% by tuning the twist angle. The maximum of the IF shift is found in the certain condition satisfied by the reflective coefficients, and the shift strongly depends on the twist angle between the optical axes of the two slabs. The spatial shifts obtained directly from the GH and IF shift definitions were provided, which indicate that the theoretical results from the stationary phase method are believable. These results may open up a new way for developing the nano-optical devices.

Ultrafast plasmon dynamics in asymmetric gold nanodimers

Bereket Dalga Dana, Alemayehu Nana Koya, Xiaowei Song(宋晓伟), and Jingquan Lin(林景全)

Chin. Phys. B, 2022, 31 (6): 064208. DOI: 10.1088/1674-1056/ac3737

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We theoretically investigate the effect of symmetry breaking on the ultrafast plasmon responses of Au nanodisk (ND) dimers by varying the diameter of one of the constituent nanodisks. In the case of a single ultrafast laser pulse, we demonstrate that the ultrafast responses of Au ND homodimer can be significantly modified due to the effect of symmetry breaking. The symmetric dimer shows a single broad spectral peak, whereas the size-asymmetric dimer shows three spectral peaks. The first system displays at most one temporal maximum and no beats in ultrafast temporal, whereas the second system may have three temporal maxima and two beats due to a combination of broken symmetry and the coherent superposition between various plasmon modes induced by the ultra-short laser pulse. Moreover, the shape of temporal dynamics of the size-asymmetric dimer is significantly deformed due to the excitation of local plasmon modes with different wavelength components. Furthermore, the decay time of the amplitude of the local field is longer and oscillates with a high frequency due to the narrower linewidth and red-shifted spectral peaks. We show that the ultrafast plasmon responses of both dimers can be controlled by varying the relative phase and time delays between a pair of two pulses. Our results will open new paths to understanding ultrafast plasmon responses in asymmetric heterodimers with suitable properties for different applications.

Molecular dynamics simulations of mechanical properties of epoxy-amine: Cross-linker type and degree of conversion effects

Yongqin Zhang(张永钦), Hua Yang(杨华), Yaguang Sun(孙亚光),Xiangrui Zheng(郑香蕊), and Yafang Guo(郭雅芳)

Chin. Phys. B, 2022, 31 (6): 064209. DOI: 10.1088/1674-1056/ac3cab

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Molecular dynamics (MD) simulations are conducted to study the thermo-mechanical properties of a family of thermosetting epoxy-amines. The crosslinked epoxy resin EPON862 with a series of cross-linkers is built and simulated under the polymer consistent force field (PCFF). Three types of curing agents (rigidity1,3-phenylenediamine (1,3-P), 4,4-diaminodiphenylmethane (DDM), and phenol-formaldehyde-ethylenediamine (PFE)) with different numbers of active sites are selected in the simulations. We focus on the effects of the cross-linkers on thermo-mechanical properties such as density, glass transition temperature (T_g), elastic constants, and strength. Our simulations show a significant increase in the T_g, Young's modulus and yield stress with the increase in the degree of conversion. The simulation results reveal that the mechanical properties of thermosetting polymers are strongly dependent on the molecular structures of the cross-linker and network topological properties, such as end-to-end distance, crosslinking density and degree of conversion.

Switchable terahertz polarization converter based on VO₂ metamaterial Suggested by editors

Haotian Du(杜皓天), Mingzhu Jiang(江明珠), Lizhen Zeng(曾丽珍), Longhui Zhang(张隆辉), Weilin Xu(徐卫林), Xiaowen Zhang(张小文), and Fangrong Hu(胡放荣)

Chin. Phys. B, 2022, 31 (6): 064210. DOI: 10.1088/1674-1056/ac4f5b

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A switchable terahertz (THz) polarization converter based on vanadium dioxide (VO₂) metamaterial is proposed. It is a 5-layer structure which containing metal split-ring-resonator (SRR), the first polyimide (PI) spacer, VO₂ film, the second PI spacer, and metal grating. It is an array structure and the period in x and y directions is 100 μm. The performance is simulated by using finite integration technology. The simulation results show that, when the VO₂ is in insulating state, the device is a transmission polarization converter. The cross-linear polarization conversion can be realized in a broadband of 0.70 THz, and the polarization conversion rate (PCR) is higher than 99%. Under thermal stimulus, the VO₂ changes from insulating state to metallic state, and the device is a reflective polarization converter. The linear-to-circular polarization conversion can be successfully realized in a broadband of 0.50 THz, and the PCR is higher than 88%.

Loss prediction of three-level amplified spontaneous emission sources in radiation environment

Shen Tan(谭深), Yan Li(李彦), Hao-Shi Zhang(张浩石), Xiao-Wei Wang(王晓伟), and Jing Jin(金靖)

Chin. Phys. B, 2022, 31 (6): 064211. DOI: 10.1088/1674-1056/ac43a8

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A model of three-level amplified spontaneous emission (ASE) sources, considering radiation effect, is proposed to predict radiation induced loss of output power in radiation environment. Radiation absorption parameters of ASE sources model are obtained by the fitting of color centers generation and recovery process of gain loss data at lower dose rate. Gain loss data at higher dose is applied for self-validating. This model takes both the influence of erbium ions absorption and photon bleaching effect into consideration, which makes the prediction of different dose and dose rate more accurate and flexible. The fitness value between ASE model and gain loss data is 99.98%, which also satisfies the extrapolation at the low dose rate. The method and model may serve as a valuable tool to predict ASE performance in harsh environment.

Quantum key distribution transmitter chip based on hybrid-integration of silica and lithium niobates

Xiao Li(李骁), Liang-Liang Wang(王亮亮), Jia-shun Zhang(张家顺), Wei Chen(陈巍), Yue Wang(王玥), Dan Wu (吴丹), and Jun-Ming An (安俊明)

Chin. Phys. B, 2022, 31 (6): 064212. DOI: 10.1088/1674-1056/ac40fe

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A quantum key distribution transmitter chip based on hybrid-integration of silica planar light-wave circuit (PLC) and lithium niobates (LN) modulator PLC is presented. The silica part consists of a tunable directional coupler and 400-ps delay line, and the LN part is made up of a Y-branch, with electro-optic modulators on both arms. The two parts are facet-coupled to form an asymmetric Mach-Zehnder interferometer. We successfully encode and decode four BB84 states at 156.25-MHz repetition rate. Fast phase-encoding of 0 or $\pi $ is achieved, with interference fringe visibilities 78.53% and 82.68% for states $|+\rangle$ and $|-\rangle$, respectively. With the aid of an extra off-chip LN intensity modulator, two time-bin states are prepared and the extinction ratios are 18.65 dB and 15.46 dB for states $|0\rangle$ and $|1\rangle$, respectively.

Single-polarization single-mode hollow-core negative curvature fiber with nested U-type cladding elements

Qi-Wei Wang(王启伟), Shi Qiu(邱石), Jin-Hui Yuan(苑金辉), Gui-Yao Zhou(周桂耀), Chang-Ming Xia(夏长明), Yu-Wei Qu(屈玉玮), Xian Zhou(周娴), Bin-Bin Yan(颜玢玢), Qiang Wu(吴强), Kui-Ru Wang(王葵如), Xin-Zhu Sang(桑新柱), and Chong-Xiu Yu(余重秀)

Chin. Phys. B, 2022, 31 (6): 064213. DOI: 10.1088/1674-1056/ac46c7

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Hollow-core negative curvature fibers (HC-NCFs) have become one of the research hotspots in the field of optical fiber because of their potential applications in the data and energy transmissions. In this work, a new kind of single-polarization single-mode HC-NCF with nested U-type cladding elements is proposed. To achieve the single-polarization single-mode transmission, we use two different silica tubes in thickness, which satisfy the resonance and anti-resonance conditions on the U-type cladding elements and the cladding tubes, respectively. Besides, the elliptical elements are introduced to achieve good single-mode performance. By studying the influences of the structure parameters on the propagation characteristics, the optimized structure parameters are obtained. The simulation results show that when the wavelength is fixed at 1550 nm, the single-polarization single-mode transmission is achieved, with the polarization extinction ratio of 25749 and minimum high-order mode extinction ratio of 174. Furthermore, the confinement loss is only 0.0015 dB/m.

Tunable spectral shift of high-order harmonic generation in atoms using a sinusoidally phase-modulated pulse Suggested by editors

Yue Qiao(乔月), Jun Wang(王俊), Yan Yan(闫妍), Simeng Song(宋思蒙), Zhou Chen(陈洲), Aihua Liu(刘爱华), Jigen Chen(陈基根), Fuming Guo(郭福明), and Yujun Yang(杨玉军)

Chin. Phys. B, 2022, 31 (6): 064214. DOI: 10.1088/1674-1056/ac2d1c

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High-order harmonic generation (HHG) from an atom illuminated by a sinusoidally phase-modulated pulse is investigated by solving the time-dependent Schrödinger equation. The spectral shift that occurs in atomic HHG can be achieved easily using our laser pulse. It is shown that the photon energy of the generated harmonics is controllable within the range of 1 eV. The shift of the frequency peak position is rooted in the asymmetry of the rising and falling parts of the laser pulse. We also show that by varying the phase parameters in the frequency domain of the laser one can adjust and control the shift in atomic harmonic spectra.

All-fiber erbium-doped dissipative soliton laser with multimode interference based on saturable-reserve saturable hybrid optical switch

Xin Zhao(赵鑫), Renyan Wan(王仁严), Weiyan Li(李卫岩), Liang Jin(金亮), He Zhang(张贺), Yan Li(李岩), Yingtian Xu(徐英添), Linlin Shi(石琳琳), and Xiaohui Ma(马晓辉)

Chin. Phys. B, 2022, 31 (6): 064215. DOI: 10.1088/1674-1056/ac5611

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Reverse saturable absorption is essential for the realization of dissipative solitons. In this paper, we introduce reverse saturable absorption by using nonlinear multimode interference (NL-MMI), for the first time, to the best of our knowledge, and obtain a stable dissipative soliton operation. By adjusting the coupling efficiency from multimode fiber to single mode fiber, the absorption properties of NL-MMI can be switched between saturation and reverse saturation. The dissipative soliton can be obtained with pulse width of 975 fs in the experiment, the 3-dB bandwidth at 1555 nm is 16 nm, and the maximum output power is 11.48 mW. The nonlinear absorption optical modulation and high damage threshold characteristics of the NL-MMI based ultrafast optical switch provide a new idea for realizing dissipative solitons.

Observation of V-type electromagnetically induced transparency and optical switch in cold Cs atoms by using nanofiber optical lattice

Xiateng Qin(秦夏腾), Yuan Jiang(蒋源), Weixin Ma(马伟鑫), Zhonghua Ji(姬中华),Wenxin Peng(彭文鑫), and Yanting Zhao(赵延霆)

Chin. Phys. B, 2022, 31 (6): 064216. DOI: 10.1088/1674-1056/ac685a

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Optical nanofiber (ONF) is a special tool to achieve the interaction between light and matter with ultralow power. In this paper, we demonstrate V-type electromagnetically induced transparency (EIT) in cold atoms trapped by an ONF-based two-color optical lattice. At an optical depth of 7.35, 90% transmission can be achieved by only 7.7 pW coupling power. The EIT peak and linewidth are investigated as a function of the coupling optical power. By modulating the pW-level control beam of the ONF-EIT system in sequence, we further achieve efficient and high contrast control of the probe transmission, as well as its potential application in the field of quantum communication and quantum information science by using one-dimensional atomic chains.

Broadband low-frequency acoustic absorber based on metaporous composite

Jia-Hao Xu(徐家豪), Xing-Feng Zhu(朱兴凤), Di-Chao Chen(陈帝超), Qi Wei(魏琦), and Da-Jian Wu(吴大建)

Chin. Phys. B, 2022, 31 (6): 064301. DOI: 10.1088/1674-1056/ac4907

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Broadband absorption of low-frequency sound waves via a deep subwavelength structure is of great and ongoing interest in research and engineering. Here, we numerically and experimentally present a design of a broadband low-frequency absorber based on an acoustic metaporous composite (AMC). The AMC absorber is constructed by embedding a single metamaterial resonator into a porous layer. The finite element simulations show that a high absorption (absorptance A>0.8) can be achieved within a broad frequency range (from 290 Hz to 1074 Hz), while the thickness of AMC is 1/13 of the corresponding wavelength at 290 Hz. The broadband and high-efficiency performances of the absorber are attributed to the coupling between the two resonant absorptions and the trapped mode. The numerical simulations and experimental results are obtained to be in good agreement with each other. Moreover, the high broadband absorption can be maintained under random incident acoustic waves. The proposed absorber provides potential applications in low-frequency noise reduction especially when limited space is demanded.

Improving sound diffusion in a reverberation tank using a randomly fluctuating surface

Qi Li(李琪), Dingding Xie(谢丁丁), Rui Tang(唐锐), Dajing Shang(尚大晶), and Zhichao Lv(吕志超)

Chin. Phys. B, 2022, 31 (6): 064302. DOI: 10.1088/1674-1056/ac3812

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Underwater reverberation environments that satisfy the conditions of uniformity and isotropy of the diffuse field can be used to measure the acoustic characteristics of underwater targets. This study combines two practical indicators — the standard deviation of the absolute sound pressure field (to indicate uniformity) and the analysis of the wavenumber spectrum in the spherical harmonics domain (to indicate isotropy) — for an accurate evaluation of the diffusion of the sound field in a reverberation tank. A method is proposed that can improve the narrow-band diffusion of the sound field by employing a randomly fluctuating surface. An acoustic experiment was performed in a reverberation water tank (1.2 m×1 m×0.8 m), where a randomly fluctuating surface was generated by making waves. The experimental results show that as the wave motion contributes effectively to the random reflection of sound rays in all directions, the uniformity and isotropy are improved significantly when the surface is fluctuating randomly. This work helps to ensure accurate measurements of the characteristics of underwater targets in reverberation tanks.

Collision enhanced hyper-damping in nonlinear elastic metamaterial

Miao Yu(于淼), Xin Fang(方鑫), Dianlong Yu(郁殿龙), Jihong Wen(温激鸿), and Li Cheng(成利)

Chin. Phys. B, 2022, 31 (6): 064303. DOI: 10.1088/1674-1056/ac48fc

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Nonlinear elastic metamaterial, a topic which has attracted extensive attention in recent years, can enable broadband vibration reduction under relatively large amplitude. The combination of damping and strong nonlinearity in metamaterials may entail extraordinary effects and offer the capability for low-frequency and broadband vibration reduction. However, there exists a clear lack of proper design methods as well as the deficiency in understanding properties arising from this concept. To tackle this problem, this paper numerically demonstrates that the nonlinear elastic metamaterials, consisting of sandwich damping layers and collision resonators, can generate very robust hyper-damping effect, conducive to efficient and broadband vibration suppression. The collision-enhanced hyper damping is persistently presented in a large parameter space, ranging from small to large amplitudes, and for small and large damping coefficients. The achieved robust effects greatly enlarge the application scope of nonlinear metamaterials. We report the design concept, properties and mechanisms of the hyper-damping and its effect on vibration transmission. This paper reveals new properties offered by nonlinear elastic metamaterials, and offers a robust method for achieving efficient low-frequency and broadband vibration suppression.

Parity-time symmetric acoustic system constructed by piezoelectric composite plates with active external circuits Suggested by editors

Yang Zhou(周扬), Zhang-Zhao Yang(杨彰昭), Yao-Yin Peng(彭尧吟), and Xin-Ye Zou(邹欣晔)

Chin. Phys. B, 2022, 31 (6): 064304. DOI: 10.1088/1674-1056/ac4e10

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Researches on parity-time (PT) symmetry in acoustic field can provide an efficient platform for controlling the travelling acoustic waves with balanced loss and gain. Here, we report a feasible design of PT-symmetric system constructed by piezoelectric composite plates with two different active external circuits. By judiciously adjusting the resistances and inductances in the external circuits, we obtain the exceptional point due to the spontaneous breaking of PT symmetry at the desired frequencies and can observe the unidirectional invisibility. Moreover, the system can be at PT exact phase or broken phase at the same frequency in the same structure by merely adjusting the external circuits, which represents the active control that makes the acoustic manipulation more convenient. Our study may provide a feasible way for manipulating acoustic waves and inspire the application of piezoelectric composite materials in acoustic structures.

Fast prediction of aerodynamic noise induced by the flow around a cylinder based on deep neural network ^Hot!

Hai-Yang Meng(孟海洋), Zi-Xiang Xu(徐自翔), Jing Yang(杨京), Bin Liang(梁彬), and Jian-Chun Cheng(程建春)

Chin. Phys. B, 2022, 31 (6): 064305. DOI: 10.1088/1674-1056/ac5e98

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Accurate and fast prediction of aerodynamic noise has always been a research hotspot in fluid mechanics and aeroacoustics. The conventional prediction methods based on numerical simulation often demand huge computational resources, which are difficult to balance between accuracy and efficiency. Here, we present a data-driven deep neural network (DNN) method to realize fast aerodynamic noise prediction while maintaining accuracy. The proposed deep learning method can predict the spatial distributions of aerodynamic noise information under different working conditions. Based on the large eddy simulation turbulence model and the Ffowcs Williams-Hawkings acoustic analogy theory, a dataset composed of 1216 samples is established. With reference to the deep learning method, a DNN framework is proposed to map the relationship between spatial coordinates, inlet velocity and overall sound pressure level. The root-mean-square-errors of prediction are below 0.82 dB in the test dataset, and the directivity of aerodynamic noise predicted by the DNN framework are basically consistent with the numerical simulation. This work paves a novel way for fast prediction of aerodynamic noise with high accuracy and has application potential in acoustic field prediction.

Accurate prediction of the critical heat flux for pool boiling on the heater substrate

Fengxun Hai(海丰勋), Wei Zhu(祝薇), Xiaoyi Yang(杨晓奕), and Yuan Deng(邓元)

Chin. Phys. B, 2022, 31 (6): 064401. DOI: 10.1088/1674-1056/ac523c

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While the influence of liquid qualities, surface morphology, and operating circumstances on critical heat flux (CHF) in pool boiling has been extensively studied, the effect of the heater substrate has not. Based on the force balance analysis, a theoretical model has been developed to accurately predict the CHF in pool boiling on a heater substrate. An analytical expression for the CHF of a heater substrate is obtained in terms of the surface thermophysical property. It is indicated that the ratio of thermal conductivity (k) to the product of density (ρ) and specific heat (c_p) is an essential substrate property that influences the CHF. By modifying the well-known force-balance-based CHF model (Kandlikar model), the thermal characteristics of the substrate are taken into consideration. The bias of predicted CHF values are within 5% compared with the experimental results.

Coupled flow and heat transfer of power-law nanofluids on non-isothermal rough rotary disk subjected to magnetic field

Yun-Xian Pei(裴云仙), Xue-Lan Zhang(张雪岚), Lian-Cun Zheng(郑连存), and Xin-Zi Wang(王鑫子)

Chin. Phys. B, 2022, 31 (6): 064402. DOI: 10.1088/1674-1056/ac46bd

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We study the coupled flow and heat transfer of power-law nanofluids on a non-isothermal rough rotating disk subjected to a magnetic field. The problem is formulated in terms of specified curvilinear orthogonal coordinate system. An improved BVP4C algorithm is proposed, and numerical solutions are obtained. The influence of volume fraction, types and shapes of nanoparticles, magnetic field and power-law index on the flow, and heat transfer behavior are discussed. The obtained results show that the power-law exponents (PLE), nanoparticle volume fraction (NVF), and magnetic field inclination angle (MFIA) have almost no effects on velocities in the wave surface direction, but have small or significant effects on the azimuth direction. The NVF has remarkable influences on local Nusselt number (LNN) and friction coefficients (FC) in the radial direction and the azimuth direction (AD). The LNN increases with NVF increasing while FC in AD decreases. The types of nanoparticles, magnetic field strength, and inclination have small effects on LNN, but they have remarkable influences on the friction coefficients with positively correlated heat transfer rate, while the inclination is negatively correlated with heat transfer rate. The size of the nanoparticle shape factor is positively correlated with LNN.

Influences of Marangoni convection and variable magnetic field on hybrid nanofluid thin-film flow past a stretching surface

Noor Wali Khan, Arshad Khan, Muhammad Usman, Taza Gul, Abir Mouldi, and Ameni Brahmia

Chin. Phys. B, 2022, 31 (6): 064403. DOI: 10.1088/1674-1056/ac3a5d

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Investigations on thin-film flow play a vital role in the field of optoelectronics and magnetic devices. Thin films are reasonably hard and thermally stable but quite fragile. The thermal stability of a thin film can be further improved by incorporating the effects of nanoparticles. In the current work, a stretchable surface is considered upon which hybrid nanofluid thin-film flow is taken into account. The idea of augmenting heat transmission by making use of a hybrid nanofluid is a focus of the current work. The flow is affected by variations in the viscous forces, along with viscous dissipation effects and Marangoni convection. A time-constrained magnetic field is applied in the normal direction to the flow system. The equations governing the flow system are shifted to a non-dimensional form by applying similarity variables. The homotopy analysis method is employed to find the solution to the resultant equations. It is noticed in this study that the flow characteristics decline with augmentation of magnetic, viscosity and unsteadiness parameters while they increase with enhanced values of thin-film parameters. Thermal characteristics are supported by increasing values of the Eckert number and the unsteadiness parameter and opposed by the viscosity parameter and Prandtl number. The numerical impact of different emerging parameters upon skin friction and the Nusselt number is calculated in tabular form. A comparison of current work with established results is carried out, with good agreement.

Hemodynamics of aneurysm intervention with different stents

Peichan Wu(吴锫婵), Yuhan Yan(严妤函), Huan Zhu(朱欢), Juan Shi(施娟), and Zhenqian Chen(陈振乾)

Chin. Phys. B, 2022, 31 (6): 064701. DOI: 10.1088/1674-1056/ac5603

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An ideal cerebral aneurysm model with different stent forms is established. By using the single-relaxation-time (SRT) lattice Boltzmann method (LBM) to solve the flow field, the blood flow characteristics in the aneurysm under different conditions are studied numerically. The intra-arterial stenting of saccular aneurysms at different Reynolds numbers and the feasibility of new stenting forms such as double stenting and variable-spacing stenting in the aneurysms are explored. The hemodynamic factors such as velocity distribution and wall shear stress (WSS) in the aneurysm are analyzed. Numerical results show that the risk of aneurysm rupture is mainly centralized at the right corner of the aneurysm. Intervention of stents in the aneurysm can effectively reduce the intra-aneurysmal velocity and WSS, and decrease the danger of aneurysm rupture during strenuous exercise or emotional excitement. At the same time, the intervention of a double stent and the stent shape with a dense anterior part in the aneurysm has certain advantages in preventing aneurysm rupture. The intra-aneurysmal mean velocity reduction can reach 90.39% and 80.29% after the intervention of the double stent and the anterior densified stent respectively.

Experimental investigation on divertor tungsten sputtering with neon seeding in ELMy H-mode plasma in EAST tokamak Suggested by editors

Dawei Ye(叶大为), Fang Ding(丁芳), Kedong Li(李克栋), Zhenhua Hu(胡振华), Ling Zhang(张凌), Xiahua Chen(陈夏华), Qing Zhang(张青), Pingan Zhao(赵平安), Tao He(贺涛), Lingyi Meng(孟令义), Kaixuan Ye(叶凯萱), Fubin Zhong(钟富彬), Yanmin Duan(段艳敏), Rui Ding(丁锐), Liang Wang(王亮), Guosheng Xu(徐国盛), Guangnan Luo(罗广南), and EAST team

Chin. Phys. B, 2022, 31 (6): 065201. DOI: 10.1088/1674-1056/ac4f58

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Neon (Ne) seeding is used to cool the edge plasma by radiation to protect the divertor tungsten (W) target in the Experimental Advanced Superconducting Tokamak (EAST). The W sputtering in the outer divertor target with Ne seeding is assessed by the divertor visible spectroscopy system. It is observed that the W sputtering flux initially increases with Ne concentration in the divertor despite the decreasing plasma temperature. After reaching a maximum around 25 eV, the W sputtering rate starts to decrease, presenting a suppression effect. The effect on the divertor W sputtering flux and yield due to the competition between the increase of the Ne concentration and the decrease of the plasma temperature is discussed. The results show that enough Ne seeding is essential to effectively reduce the electron temperature and thus to suppress W sputtering. Moreover, ELM suppression is observed when Ne and W impurities enter the core plasma, which could be correlated to the enhanced turbulence transport in the pedestal.

Quantitative simulations of ratchet potential in a dusty plasma ratchet Suggested by editors

Shuo Wang(王硕), Ning Zhang(张宁), Shun-Xin Zhang(张顺欣), Miao Tian(田淼), Ya-Wen Cai(蔡雅文), Wei-Li Fan(范伟丽), Fu-Cheng Liu(刘富成), and Ya-Feng He(贺亚峰)

Chin. Phys. B, 2022, 31 (6): 065202. DOI: 10.1088/1674-1056/ac46c4

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Using a dusty plasma ratchet, one can realize the rectification of charged dust particle in a plasma. To obtain the ratchet potential dominating the rectification, here we perform quantitative simulations based on a two-dimensional fluid model of capacitively coupled plasma. Plasma parameters are firstly calculated in two typical cross sections of the dusty plasma ratchet which cut vertically the saw channel at different azimuthal positions. The balance positions of charged dust particle in the two cross sections then can be found exactly. The electric potentials at the two balance positions have different values. Using interpolation in term of a double-sine function from previous experimental measurement, an asymmetrical ratchet potential along the saw channel is finally obtained. The asymmetrical orientation of the ratchet potential depends on discharge conditions. Quantitative simulations further reproduce our previous experimental phenomena such as the rectification of dust particle in the dusty plasma ratchet.

Effect of the magnetization parameter on electron acceleration during relativistic magnetic reconnection in ultra-intense laser-produced plasma

Qian Zhang(张茜), Yongli Ping(平永利), Weiming An(安维明), Wei Sun(孙伟), and Jiayong Zhong(仲佳勇)

Chin. Phys. B, 2022, 31 (6): 065203. DOI: 10.1088/1674-1056/ac3397

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Relativistic magnetic reconnection (MR) driven by two ultra-intense lasers with different spot separation distances is simulated by a three-dimensional (3D) kinetic relativistic particle-in-cell (PIC) code. We find that changing the separation distance between two laser spots can lead to different magnetization parameters of the laser plasma environment. As the separation distance becomes larger, the magnetization parameter σ becomes smaller. The electrons are accelerated in these MR processes and their energy spectra can be fitted with double power-law spectra whose index will increase with increasing separation distance. Moreover, the collisionless shocks' contribution to energetic electrons is close to the magnetic reconnection contribution with σ decreasing, which results in a steeper electron energy spectrum. Basing on the 3D outflow momentum configuration, the energetic electron spectra are recounted and their spectrum index is close to 1 in these three cases because the magnetization parameter σ is very high in the 3D outflow area.

Study on divertor plasma behavior through sweeping strike point in new lower divertor on EAST Suggested by editors

Yu-Qiang Tao(陶余强), Guo-Sheng Xu(徐国盛), Ling-Yi Meng(孟令义), Rui-Rong Liang(梁瑞荣), Lin Yu(余林), Xiang Liu(刘祥), Ning Yan(颜宁), Qing-Quan Yang(杨清泉), Xin Lin(林新), and Liang Wang(王亮)

Chin. Phys. B, 2022, 31 (6): 065204. DOI: 10.1088/1674-1056/ac4a65

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A series of L-mode discharges have been conducted in the new ‘corner slot’ divertor on the Experimental Advanced Superconducting Tokamak (EAST) to study the divertor plasma behavior through sweeping strike point. The plasma control system controls the strike point sweeping from the horizontal target to the vertical target through poloidal field coils, with keeping the main plasma stability. The surface temperature of the divertor target cools down as the strike point moves away, indicating that sweeping strike point mitigates the heat load. To avoid the negative effect of probe tip damage, a method based on sweeping strike point is used to get the normalized profile and study the decay length of particle and heat flux on the divertor target λ_js, λ_q. In the discharges with high radio-frequency (RF) heating power, electron temperature T_e is lower and λ_js is larger when the strike point locates on the horizontal target compared to the vertical target, probably due to the corner effect. In the Ohmic discharges, λ_js, λ_q are much larger compared to the discharges with high RF heating power, which may be attributed to lower edge T_e.

Influence of oxygen addition on the discharge characteristics of an argon plasma jet at atmospheric pressure

Junyu Chen(陈俊宇), Na Zhao(赵娜), Jiacun Wu(武珈存), Kaiyue Wu(吴凯玥), Furong Zhang(张芙蓉),Junxia Ran(冉俊霞), Pengying Jia(贾鹏英), Xuexia Pang(庞学霞), and Xuechen Li(李雪辰)

Chin. Phys. B, 2022, 31 (6): 065205. DOI: 10.1088/1674-1056/ac601a

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Plasma jet is an important low-temperature plasma source in extensive application fields. To promote the production of active oxygen species, oxygen is often introduced into the inert working gas. However, the influence of oxygen content on the discharge characteristics of an argon plasma jet is not clear. Aim to this status, an argon plasma jet in a single-electrode geometry is employed to investigate the influence of oxygen concentration (C_O) on discharge aspects. Results indicate that with increasing C_O (≤ 0.6%), the plume transits from a diffuse morphology to a hollow structure. Electrical and optical measurements reveal that both discharge number per voltage cycle and pulse intensity alter with varying C_O. Moreover, discharge morphologies of negative and positive discharges obtained by fast photograph also shift with varying C_O. Besides, optical emission spectra are collected to investigate atomic C_O, electron density, and electron temperature. The results mentioned above are explained qualitatively, which are believed to be of great significance for the applications of atmospheric pressure plasma jet.

A nonlinear wave coupling algorithm and its programing and application in plasma turbulences

Yong Shen(沈勇), Yu-Hang Shen(沈煜航), Jia-Qi Dong(董家齐), Kai-Jun Zhao(赵开君), Zhong-Bing Shi(石中兵), and Ji-Quan Li(李继全)

Chin. Phys. B, 2022, 31 (6): 065206. DOI: 10.1088/1674-1056/ac4233

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The fully developed turbulence can be regarded as a nonlinear system, with wave coupling inside, which causes the nonlinear energy to transfer, and drives the turbulence to develop further or be suppressed. Spectral analysis is one of the most effective methods to study turbulence system. In order to apply it to the study of the nonlinear wave coupling process of edge plasma turbulence, an efficient algorithm based on spectral analysis technology is proposed to solve the nonlinear wave coupling equation. The algorithm is based on a mandatory temporal static condition with the nonideal spectra separated from the ideal spectra. The realization idea and programing flow are given. According to the characteristics of plasma turbulence, the simulation data are constructed and used to verify the algorithm and its implementation program. The simulation results and experimental results show the accuracy of the algorithm and the corresponding program, which can play a great role in the studying the energy transfer in edge plasma turbulences. As an application, the energy cascade analysis of typical edge plasma turbulence is carried out by using the results of a case calculation. Consequently, a physical picture of the energy transfer in a kind of fully developed turbulence is constructed, which confirms that the energy transfer in this turbulent system develops from lower-frequency region to higher-frequency region and from linear growing wave to damping wave.

Role of the zonal flow in multi-scale multi-mode turbulence with small-scale shear flow in tokamak plasmas

Hui Li(李慧), Jiquan Li(李继全), Zhengxiong Wang(王正汹), Lai Wei(魏来), and Zhaoqing Hu(胡朝清)

Chin. Phys. B, 2022, 31 (6): 065207. DOI: 10.1088/1674-1056/ac6011

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The structural characteristics of zonal flows and their roles in the nonlinear interaction of multi-scale multi-mode turbulence are investigated numerically via a self-consistent Landau-fluid model. The multi-mode turbulence here is composed of a shorter wavelength electromagnetic (EM) ion temperature gradient (ITG) mode and a Kelvin-Helmholtz (KH) instability with long wavelengths excited by externally imposed small-scale shear flows. For strong shear flow, a prominent periodic intermittency of fluctuation intensity except for dominant ITG component is revealed in turbulence evolution, which onset time depends on the ion temperature gradient and the shear flow amplitudes corresponding to different KH instabilities. It is identified that the intermittency phenomenon results from the zonal flow dynamics, which is mainly generated by the KH mode and back-reacts on it. It is demonstrated that the odd symmetric components of zonal flow (same symmetry as the external flow) make the radial parity of the KH mode alteration through adjusting the drift velocities at two sides of the resonant surface so that the KH mode becomes bursty first. Afterwards, the ITG intermittency follows due to nonlinear mode coupling. Parametric dependences of the features of the intermittency are elaborated. Finally, associated turbulent heat transport is evaluated.

Structure, phase evolution and properties of Ta films deposited using hybrid high-power pulsed and DC magnetron co-sputtering

Min Huang(黄敏), Yan-Song Liu(刘艳松), Zhi-Bing He(何智兵), and Yong Yi(易勇)

Chin. Phys. B, 2022, 31 (6): 066101. DOI: 10.1088/1674-1056/ac43a9

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Crystalline phase and microstructure control are critical for obtaining desired properties of Ta films deposited by magnetron sputtering. Structure, phase evolution and properties of Ta films deposited by using hybrid high power impulse magnetron sputtering (HiPIMS) and direct current magnetron sputtering (DCMS) under different fractions of DCMS power were investigated, where Ta ion to Ta neutral ratios of the deposition flux were changed. The results revealed that the number of Ta ions arriving on the substrate/growing film plays an important role in structure and phase evolution of Ta films. It can effectively avoid the unstable arc discharge under low pressure and show a higher deposition rate by combining HiPIMS and DCMS compared with only HiPIMS. Meanwhile, the high hardness α -Ta films can be directly deposited by hybrid co-sputtering compared to those prepared by DCMS. In the co-sputtering technology, pure α -Ta phase films with extremely fine, dense and uniform crystal grains were obtained, which showed smooth surface roughness (3.22 nm), low resistivity (38.98 μΩ · cm) and abnormal high hardness (17.64 GPa).

Vacuum current-carrying tribological behavior of MoS₂-Ti films with different conductivities

Lu-Lu Pei(裴露露), Peng-Fei Ju(鞠鹏飞), Li Ji(吉利), Hong-Xuan Li(李红轩),Xiao-Hong Liu(刘晓红), Hui-Di Zhou(周惠娣), and Jian-Min Chen(陈建敏)

Chin. Phys. B, 2022, 31 (6): 066201. DOI: 10.1088/1674-1056/ac4f5a

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Current-carrying sliding is widely applied in aerospace equipment, but it is limited by the poor lubricity of the present materials and the unclear tribological mechanism. This study demonstrated the potential of MoS₂-based materials with excellent lubricity as space sliding electrical contact materials by doping Ti to improve its conductivity. The tribological behavior of MoS₂-Ti films under current-carrying sliding in vacuum was studied by establishing a simulation evaluating device. Moreover, the noncurrent-carrying sliding and static current-carrying experiments in vacuum were carried out for comparison to understand the tribological mechanism. In addition to mechanical wear, the current-induced arc erosion and thermal effect take important roles in accelerating the wear. Arc erosion is caused by the accumulation of electric charge, which is related to the conductivity of the film. While the current-thermal effect softens the film, causing strong adhesive wear, and good conductivity and the large contact area are beneficial for minimizing the thermal effect. So the moderate hardness and good conductivity of MoS₂-Ti film contribute to its excellent current-carrying tribological behavior in vacuum, showing a significant advantage compared with the traditional ones.

Evolution of surfaces and mechanisms of contact electrification between metals and polymers

Lin-Feng Wang(王林锋), Yi Dong(董义), Min-Hao Hu(胡旻昊), Jing Tao(陶静), Jin Li(李进), and Zhen-Dong Dai(戴振东)

Chin. Phys. B, 2022, 31 (6): 066202. DOI: 10.1088/1674-1056/ac4a5f

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Contact electrification (CE) is a pretty common phenomenon, but still is poorly understood. The long-standing controversy over the mechanisms of CE related to polymers is particularly intense due to their complexity. In this paper, the CE between metals and polymers is systematically studied, which shows the evolution of surfaces is accompanied by variations of CE outputs. The variations of CE charge quantity are closely related to the creep and deformation of the polymer and metal surfaces. Then the relationship between CE and polymer structures is put forward, which is essentially determined by the electronegativity of elements and the functional groups in the polymers. The effects of load and contact frequency on the CE process and outputs are also investigated, indicating the increase of CE charge quantity with load and frequency. Material transfer from polymer to metal is observed during CE while electrons transfer from metal to polymer, both of which are believed to have an influence on each other. The findings advance our understanding of the mechanism of CE between metal and polymers, and provides insights into the performance of CE-based application in various conditions, which sheds light on the design and optimization of CE-based energy harvest and self-powered sensing devices.

Effect of void size and Mg contents on plastic deformation behaviors of Al-Mg alloy with pre-existing void: Molecular dynamics study

Ning Wei(魏宁), Ai-Qiang Shi(史爱强), Zhi-Hui Li(李志辉), Bing-Xian Ou(区炳显), Si-Han Zhao(赵思涵), and Jun-Hua Zhao(赵军华)

Chin. Phys. B, 2022, 31 (6): 066203. DOI: 10.1088/1674-1056/ac4a74

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The plastic deformation properties of cylindrical pre-void aluminum-magnesium (Al-Mg) alloy under uniaxial tension are explored using molecular dynamics simulations with embedded atom method (EAM) potential. The factors of Mg content, void size, and temperature are considered. The results show that the void fraction decreases with increasing Mg in the plastic deformation, and it is almost independent of Mg content when Mg is beyond 5%. Both Mg contents and stacking faults around the void affect the void growth. These phenomena are explained by the dislocation density of the sample and stacking faults distribution around the void. The variation trends of yield stress caused by void size are in good agreement with the Lubarda model. Moreover, temperature effects are explored, the yield stress and Young's modulus obviously decrease with temperature. Our results may enrich and facilitate the understanding of the plastic mechanism of Al-Mg with defects or other alloys.

Strengthening and softening in gradient nanotwinned FCC metallic multilayers Suggested by editors

Yuanyuan Tian(田圆圆), Gangjie Luo(罗港杰), Qihong Fang(方棋洪), Jia Li(李甲), and Jing Peng(彭静)

Chin. Phys. B, 2022, 31 (6): 066204. DOI: 10.1088/1674-1056/ac4cc6

Abstract ( 431 )

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Plastic-deformation behaviors of gradient nanotwinned (GNT) metallic multilayers are investigated in nanoscale via molecular dynamics simulation. The evolution law of deformation behaviors of GNT metallic multilayers with different stacking fault energies (SFEs) during nanoindentation is revealed. The deformation behavior transforms from the dislocation dynamics to the twinning/detwinning in the GNT Ag, Cu, to Al with SFE increasing. In addition, it is found that the GNT Ag and GNT Cu strengthen in the case of a larger twin gradient based on more significant twin boundary (TB) strengthening and dislocation strengthening, while the GNT Al softens due to more TB migration and dislocation nucleation from TB at a larger twin gradient. The softening mechanism is further analyzed theoretically. These results not only provide an atomic insight into the plastic-deformation behaviors of certain GNT metallic multilayers with different SFEs, but also give a guideline to design the GNT metallic multilayers with required mechanical properties.

Bandgap evolution of Mg₃N₂ under pressure: Experimental and theoretical studies

Gang Wu(吴刚), Lu Wang(王璐), Kuo Bao(包括), Xianli Li(李贤丽), Sheng Wang(王升), and Chunhong Xu(徐春红)

Chin. Phys. B, 2022, 31 (6): 066205. DOI: 10.1088/1674-1056/ac4cbe

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Wide bandgap semiconductors are crucially significant for optoelectronic and thermoelectric device applications. Metal nitride is a class of semiconductor material with great potential. Under high pressure, the bandgap of magnesium nitride was predicted to grow. Raman spectra, ultra-violet-visible (UV-Vis) absorption spectra, and first-principles calculations were employed in this study to analyze the bandgap evolution of Mg₃N₂. The widening of the bandgap has been first detected experimentally, with the gap increasing from 2.05 eV at 3 GPa to 2.88 eV at 47 GPa. According to the calculation results, the enhanced covalent component is responsible for the bandgap widening.

Reaction mechanism of metal and pyrite under high-pressure and high-temperature conditions and improvement of the properties

Yao Wang(王遥), Dan Xu(徐丹), Shan Gao(高姗), Qi Chen(陈启), Dayi Zhou(周大义), Xin Fan(范鑫), Xin-Jian Li(李欣健), Lijie Chang(常立杰),Yuewen Zhang(张跃文), Hongan Ma(马红安), and Xiao-Peng Jia(贾晓鹏)

Chin. Phys. B, 2022, 31 (6): 066206. DOI: 10.1088/1674-1056/ac4a72

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Pyrite tailings are the main cause of acid mine wastewater. We propose an idea to more effectively use pyrite, and it is modified by exploiting the reducibility of metal represented by Al under high-pressure and high-temperature (HPHT) conditions. Upon increasing the Al addition, the conductivity of pyrite is effectively improved, which is nearly 734 times higher than that of unmodified pyrite at room temperature. First-principles calculations are used to determine the influence of a high pressure on the pyrite lattice. The high pressure increases the thermal stability of pyrite, reduces pyrite to high-conductivity Fe₇S₈ (pyrrhotite) by Al. Through hardness and density tests the influence of Al addition on the hardness and toughness of samples is explored. Finally we discuss the possibility of using other metal-reducing agents to improve the properties of pyrite.

Isotropic negative thermal expansion and its mechanism in tetracyanidoborate salt CuB(CN)₄ Suggested by editors

Chunyan Wang(王春艳), Qilong Gao(高其龙), Andrea Sanson, and Yu Jia(贾瑜)

Chin. Phys. B, 2022, 31 (6): 066501. DOI: 10.1088/1674-1056/ac6019

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The control of thermal expansion is essential in applications where thermal stability is required from fiber optics coatings, high performance fuel cell cathodes to tooth fillings. Negative thermal expansion (NTE) materials, although rare, are fundamental for this purpose. This work focuses on studying tetracyanidoborate salt CuB(CN)₄, an interesting cubic-structure material that displays large isotropic NTE. A joint study of synchrotron x-ray diffraction, temperature-dependent Raman spectroscopy, and lattice dynamics calculations was conducted, showing that not only low-frequency optical modes (transverse thermal vibrations of N and C atoms) but also the acoustic modes (the vibrations of Cu atoms as a collective torsion of the neighboring atoms), contribute to NTE. As a result, new insights were gained into the NTE mechanism of CuB(CN)₄ and related framework materials.

Gate tunable Rashba spin-orbit coupling at CaZrO₃/SrTiO₃ heterointerface Suggested by editors

Wei-Min Jiang(姜伟民), Qiang Zhao(赵强), Jing-Zhuo Ling(凌靖卓), Ting-Na Shao(邵婷娜), Zi-Tao Zhang(张子涛), Ming-Rui Liu(刘明睿), Chun-Li Yao(姚春丽), Yu-Jie Qiao(乔宇杰), Mei-Hui Chen(陈美慧), Xing-Yu Chen(陈星宇), Rui-Fen Dou(窦瑞芬), Chang-Min Xiong(熊昌民), and Jia-Cai Nie(聂家财)

Chin. Phys. B, 2022, 31 (6): 066801. DOI: 10.1088/1674-1056/ac5396

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High mobility quasi two-dimensional electron gas (2DEG) found at the CaZrO₃/SrTiO₃ nonpolar heterointerface is attractive and provides a platform for the development of functional devices and nanoelectronics. Here we report that the carrier density and mobility at low temperature can be tuned by gate voltage at the CaZrO₃/SrTiO₃ interface. Furthermore, the magnitude of Rashba spin-orbit interaction can be modulated and increases with the gate voltage. Remarkably, the diffusion constant and the spin-orbit relaxation time can be strongly tuned by gate voltage. The diffusion constant increases by a factor of ～ 19.98 and the relaxation time is reduced by a factor of over three orders of magnitude while the gate voltage is swept from -50 V to 100 V. These findings not only lay a foundation for further understanding the underlying mechanism of Rashba spin-orbit coupling, but also have great significance in developing various oxide functional devices.

Surface electron doping induced double gap opening in T_d-WTe₂ Suggested by editors

Qi-Yuan Li(李启远), Yang-Yang Lv(吕洋洋), Yong-Jie Xu(徐永杰), Li Zhu(朱立), Wei-Min Zhao(赵伟民), Yanbin Chen(陈延彬), and Shao-Chun Li(李绍春)

Chin. Phys. B, 2022, 31 (6): 066802. DOI: 10.1088/1674-1056/ac632e

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By using scanning tunneling microscopy, we investigated the electronic evolution of T_d-WTe₂ via in-situ surface alkali K atoms deposition. The T_d-WTe₂ surface is electron doped upon K deposition, and as the K coverage increases, two gaps are sequentially opened near Fermi energy, which probably indicates that two phase transitions concomitantly occur during electron doping. The two gaps both show a dome-like dependence on the K coverage. While the bigger gap shows no prominent dependence on the magnetic field, the smaller one can be well suppressed and thus possibly corresponds to the superconducting transition. This work indicates that T_d-WTe₂ exhibits rich quantum states closely related to the carrier concentration.

Interfacial defect engineering and photocatalysis properties of hBN/MX₂ (M = Mo, W, and X = S, Se heterostructures Suggested by editors

Zhi-Hai Sun(孙志海), Jia-Xi Liu(刘佳溪), Ying Zhang(张颖), Zi-Yuan Li(李子源), Le-Yu Peng(彭乐宇), Peng-Ru Huang(黄鹏儒), Yong-Jin Zou(邹勇进), Fen Xu(徐芬), and Li-Xian Sun(孙立贤)

Chin. Phys. B, 2022, 31 (6): 067101. DOI: 10.1088/1674-1056/ac43b2

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Van der Waals (VDW) heterostructures have attracted significant research interest due to their tunable interfacial properties and potential applications in many areas such as electronics, optoelectronic, and heterocatalysis. In this work, the influences of interfacial defects on the electronic structures and photocatalytic properties of hBN/MX₂ (M = Mo, W, and X=S, Se) are studied using density functional theory calculations. The results reveal that the band alignment of hBN/MX₂ can be adjusted by introducing vacancies and atomic doping. The type-I band alignment of the host structure is maintained in the heterostructure with n-type doping in the hBN sublayer. Interestingly, the band alignment changed into the type-II heterostructrue due to V_B defect and p-type doping is introduced into the hBN sublayer. This can conduce to the separation of photo-generated electron-hole pairs at the interfaces, which is highly desired for heterostructure photocatalysis. In addition, two Z-type heterostructures including hBN(Be_B)/MoS₂, hBN(Be_B)/MoSe₂, and hBN(V_N)/MoSe₂ are achieved, showing the decreasing of band gap and ideal redox potential for water splitting. Our results reveal the possibility of engineering the interfacial and photocatalysis properties of hBN/MX₂ heterostructures via interfacial defects.

Polarization-dependent ultrafast carrier dynamics in GaAs with anisotropic response

Ya-Chao Li(李亚超), Chao Ge(葛超), Peng Wang(汪鹏), Shuang Liu(刘爽), Xiao-Ran Ma(麻晓冉), Bing Wang(王冰), Hai-Ying Song(宋海英), and Shi-Bing Liu(刘世炳)

Chin. Phys. B, 2022, 31 (6): 067102. DOI: 10.1088/1674-1056/ac422b

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The transient dynamics of anisotropic properties of GaAs was systematically studied by polarization-dependent ultrafast time-resolved transient absorption. Our findings revealed that the anisotropy of reflectivity was enhanced in both pump-induced and probe-induced processes, suggesting an extraordinary resonance absorption of photon-phonon coupling (PPC) with intrinsic anisotropic characteristic in carrier relaxation, regardless of the concrete crystallinity and orientation of GaAs sample. The results, delivering in-depth cognition about the polarization-dependent ultrafast carrier dynamics, also proved the paramount importance of interaction between polarized laser and semiconductor.

Effect of strain on charge density wave order in α-U

Liuhua Xie(谢刘桦), Hongkuan Yuan(袁宏宽), and Ruizhi Qiu(邱睿智)

Chin. Phys. B, 2022, 31 (6): 067103. DOI: 10.1088/1674-1056/ac4f4d

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The effect of strain on charge density wave (CDW) order in $\alpha$-U is investigated within the framework of relativistic density-functional theory. The energetical stability of $\alpha$-U with CDW distortion is enhanced by the tensile strain along $a$ and $b$ axes, which is similar to the case of negative pressure and normal. However, the tensile strain along $c$ axis suppresses the energetical stability of CDW phase. This abnormal effect could be understood from the emergence of a new one-dimensional atomic chain along $c$ axis in $\alpha$-U. Furthermore, this effect is supported by the calculations of Fermi surface and phonon mode, in which the topological objects and the dynamical instability show opposite behaviors between strains along $a$/$b$ and $c$ axes.

Uniaxial stress effect on quasi-one-dimensional Kondo lattice CeCo₂Ga₈ ^Hot!

Kangqiao Cheng(程康桥), Binjie Zhou(周斌杰), Cuixiang Wang(王翠香), Shuo Zou(邹烁), Yupeng Pan(潘宇鹏), Xiaobo He(何晓波), Jian Zhang(张健), Fangjun Lu(卢方君), Le Wang(王乐), Youguo Shi(石友国), and Yongkang Luo(罗永康)

Chin. Phys. B, 2022, 31 (6): 067104. DOI: 10.1088/1674-1056/ac6339

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Quantum critical phenomena in the quasi-one-dimensional limit remain an open issue. We report the uniaxial stress effect on the quasi-one-dimensional Kondo lattice CeCo$_2$Ga$_8$ by electric transport and AC heat capacity measurements. CeCo$_2$Ga$_8$ is speculated to sit in close vicinity but on the quantum-disordered side of a quantum critical point. Upon compressing the ${c}$ axis, parallel to the Ce-Ce chain, the onset of coherent Kondo effect is enhanced. In contrast, the electronic specific heat diverges more rapidly at low temperature when the intra-chain distance is elongated by compressions along ${a}$ or ${b}$ axis. These results suggest that a tensile intra-chain strain ($\varepsilon_c >0$) pushes CeCo$_2$Ga$_8$ closer to the quantum critical point, while a compressive intra-chain strain ($\varepsilon_c<0$) likely causes departure. Our work provides a rare paradigm of manipulation near a quantum critical point in a quasi-1D Kondo lattice by uniaxial stress, and paves the way for further investigations on the unique feature of quantum criticality in the quasi-1D limit.

Spin freezing in the van der Waals material Mn₂Ga₂S₅ ^Hot!

Jie Shen(沈洁), Xitong Xu(许锡童), Miao He(何苗), Yonglai Liu(刘永来), Yuyan Han(韩玉岩), and Zhe Qu(屈哲)

Chin. Phys. B, 2022, 31 (6): 067105. DOI: 10.1088/1674-1056/ac657c

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Geometrical frustration in low-dimensional magnetic systems has been an intriguing research aspect, where the suppression of conventional magnetic order may lead to exotic ground states such as spin glass or spin liquid. In this work we report the synthesis and magnetism study of the monocrystalline Mn$_2$Ga$_2$S$_5$, featuring both the van der Waals structure and a bilayered triangular Mn lattice. Magnetic susceptibility reveals a significant antiferromagnetic interaction with a Curie-Weiss temperature $\theta_{\rm w}\sim-260$ K and a high spin $S=5/2$ Mn$^{2+}$ state. However, no long range magnetic order has been found down to 2 K, and a spin freezing transition is found to occur at around 12 K well below its $\theta_{\rm w}$. This yields a frustration index of $f = -\theta_{\rm w}/T_{\rm f} \approx 22$, an indication that the system is highly frustrated. The absence of a double-peak structure in magnetic specific heat compared with the $TM_2$S$_4$ compounds implies that the spin freezing behavior in Mn$_2$Ga$_2$S$_5$ is a result of the competition between exchange interactions and the 2D crystalline structure. Our results suggest that the layered Mn$_2$Ga$_2$S$_5$ would be an excellent candidate for investigating the physics of 2D magnetism and spin disordered state.

Experimental observation of pseudogap in a modulation-doped Mott insulator: Sn/Si(111)-(√30×√30)R30° ^Hot!

Yan-Ling Xiong(熊艳翎), Jia-Qi Guan(关佳其), Rui-Feng Wang(汪瑞峰), Can-Li Song(宋灿立), Xu-Cun Ma(马旭村), and Qi-Kun Xue(薛其坤)

Chin. Phys. B, 2022, 31 (6): 067401. DOI: 10.1088/1674-1056/ac65f2

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Unusual quantum phenomena usually emerge upon doping Mott insulators. Using a molecular beam epitaxy system integrated with cryogenic scanning tunneling microscope, we investigate the electronic structure of a modulation-doped Mott insulator Sn/Si(111)-($\sqrt{3}\times \sqrt{3})R$30$^\circ$. In underdoped regions, we observe a universal pseudogap opening around the Fermi level, which changes little with the applied magnetic field and the occurrence of Sn vacancies. The pseudogap gets smeared out at elevated temperatures and alters in size with the spatial confinement of the Mott insulating phase. Our findings, along with the previously observed superconductivity at a higher doping level, are highly reminiscent of the electronic phase diagram in the doped copper oxide compounds.

Photothermal-chemical synthesis of P-S-H ternary hydride at high pressures

Tingting Ye(叶婷婷), Hong Zeng(曾鸿), Peng Cheng(程鹏), Deyuan Yao(姚德元), Xiaomei Pan(潘孝美), Xiao Zhang(张晓), and Junfeng Ding(丁俊峰)

Chin. Phys. B, 2022, 31 (6): 067402. DOI: 10.1088/1674-1056/ac5604

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The recent discovery of room temperature superconductivity (283 K) in carbonaceous sulfur hydride (C-S-H) has attracted much interest in ternary hydrogen rich materials. In this report, ternary hydride P-S-H was synthesized through a photothermal-chemical reaction from elemental sulfur (S), phosphorus (P) and molecular hydrogen (H₂) at high pressures and room temperature. Raman spectroscopy under pressure shows that H₂S and PH₃ compounds are synthesized after laser heating at 0.9 GPa, and a ternary van der Waals compound P-S-H is synthesized with further compression to 4.6 GPa. The P-S-H compound is probably a mixed alloy of PH₃ and (H₂S)₂H₂ with a guest-host structure similar to the C-S-H system. The ternary hydride can persist up to 35.6 GPa at least and shows two phase transitions at approximately 23.6 GPa and 32.8 GPa, respectively.

Magnetic and magnetocaloric effect in a stuffed honeycomb polycrystalline antiferromagnet GdInO₃

Yao-Dong Wu(吴耀东), Wei-Wei Duan(段薇薇), Qiu-Yue Li(李秋月), Yong-Liang Qin(秦永亮),Zhen-Fa Zi(訾振发), and Jin Tang(汤进)

Chin. Phys. B, 2022, 31 (6): 067501. DOI: 10.1088/1674-1056/ac43a1

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The magnetic and magnetocaloric properties were studied in a stuffed honeycomb polycrystalline antiferromagnet GdInO₃. The onset temperature of antiferromagnetic ordering was observed at ～ 2.1 K. Negligible thermal and magnetic hystereses suggest a reversible magnetocaloric effect (MCE) in the GdInO₃ compound. In the magnetic field changes of 0 kOe-50 kOe and 0 kOe-70 kOe, the maximum magnetic entropy change values are 9.65 J/kg· K and 18.37 J/kg· K, respectively, near the liquid helium temperature, with the corresponding relative cooling power values of 115.01 J/kg and 211.31 J/kg. The MCE investigation of the polycrystalline GdInO₃ serves to illuminate more exotic properties in this frustrated stuffed honeycomb magnetic system.

Non-volatile multi-state magnetic domain transformation in a Hall balance ^Hot!

Yang Gao(高阳), Jingyan Zhang(张静言), Pengwei Dou(窦鹏伟), Zhuolin Li(李卓霖), Zhaozhao Zhu(朱照照), Yaqin Guo(郭雅琴), Chaoqun Hu(胡超群), Weidu Qin(覃维都), Congli He(何聪丽), Shipeng Shen(申世鹏), Ying Zhang(张颖), and Shouguo Wang(王守国)

Chin. Phys. B, 2022, 31 (6): 067502. DOI: 10.1088/1674-1056/ac65f5

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High performance of the generation, stabilization and manipulation of magnetic skyrmions prompts the application of topological multilayers in spintronic devices. Skyrmions in synthetic antiferromagnets (SAF) have been considered as a promising alternative to overcome the limitations of ferromagnetic skyrmions, such as the skyrmion Hall effect and stray magnetic field. Here, by using the Lorentz transmission electron microscopy, the interconversion between the single domain, labyrinth domain and skyrmion state can be observed by the combined manipulation of electric current and magnetic field in a Hall balance (a SAF with the core structure of [Co/Pt]₄/NiO/[Co/Pt]₄ showing perpendicular magnetic anisotropy). Furthermore, high-density room temperature skyrmions can be stabilized at zero field while the external stimulus is removed and the skyrmion density is tunable. The generation and manipulation method of skyrmions in Hall balance in this study opens up a promising way to engineer SAF-skyrmion-based memory devices.

Exploration of structural, optical, and photoluminescent properties of (1-x)NiCo₂O₄/xPbS nanocomposites for optoelectronic applications

Zein K Heiba, Mohamed Bakr Mohamed, Noura M Farag, and Ali Badawi

Chin. Phys. B, 2022, 31 (6): 067801. DOI: 10.1088/1674-1056/ac4235

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The (1-x)NiCo₂O₄/xPbS (0≤ x≤ 0.2) nanocomposite samples are synthesized using the hydrothermal and thermolysis procedures. The different phases developed in the obtained nanocomposite samples are accurately determined using the x-ray diffraction technique equipped with a line-detector. The percentage of the formed phases (NiCo₂O₄ (NCO), PbS, PbSO₄), structural and microstructure parameters are determined using Rietveld quantitative phase analysis. The transmission electron microscope (TEM) images and Rietveld analysis reveal almost isotropic particle size in the nano range with a very narrow size distribution. The obtained phase percentage of PbS and PbSO₄ are smaller than nominated values (x) suggesting dissolving of some Pb and S ions into NCO which is then confirmed by the analysis of Fourier-transform infrared (FTIR) spectra of nanocomposite samples. The absorption spectra are modified upon doping NCO with PbS. The optical band gaps of the nanocomposites increase as the amount of PbS augments. The effect of alloying on extinction coefficient, refractive index, dielectric constant, optical conductivity, the intensity, and emitted color from the photoluminescence of the nanocomposite samples are also studied. The refractive index value of NCO and NCO-PbS nanocomposite samples exhibit normal dispersions. The photoluminescent measurements reveal that the NCO-PbS nanocomposites can emit a violet color. The improvement in the values of the nonlinear optical (NLO) parameters of pristine NCO at high frequencies or the nanocomposite samples at low frequencies, are made them used in NLO photonic devices.

Dynamically controlled asymmetric transmission of linearly polarized waves in VO₂-integrated Dirac semimetal metamaterials Suggested by editors

Man Xu(许曼), Xiaona Yin(殷晓娜), Jingjing Huang(黄晶晶), Meng Liu(刘蒙), Huiyun Zhang(张会云), and Yuping Zhang(张玉萍)

Chin. Phys. B, 2022, 31 (6): 067802. DOI: 10.1088/1674-1056/ac4bd3

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We numerically demonstrated a novel chiral metamaterial to achieve broadband asymmetric transmission (AT) of linearly polarized electromagnetic waves in terahertz (THz) band. The proposed metamaterial unit cell exhibits no rotational symmetry with vanadium dioxide (VO$_{2}$) inclusion embedded between Dirac semimetals (DSMs) pattern. The resonant frequency of AT can be dynamically tunable by varying the Fermi energy ($E_{\rm F}$) of the DSMs. The insulator-to-metal phase transition of VO$_{2}$ enables the amplitude of the AT to be dynamically tailored. The transmission coefficient $|T_{yx}|$ can be adjusted from 0.756 to nearly 0 by modifying the conductivity of VO$_{2}$. Meanwhile, the AT parameter intensity of linearly polarized incidence can be actively controlled from 0.55 to almost 0, leading to a switch for AT. When VO$_{2}$ is in its insulator state, the proposed device achieves broadband AT parameter greater than 0.5 from 1.21 THz to 1.80 THz with a bandwidth of 0.59 THz. When the incident wave propagates along the backward ($-z$) direction, the cross-polarized transmission $|T_{yx}|$ reaches a peak value 0.756 at 1.32 THz, whereas the value of $|T_{xy}|$ well below 0.157 in the concerned frequency. On the other hand, the co-polarized transmission $|T_{xx}|$ and $|T_{yy}|$ remained equal in the whole frequency range. This work provides a novel approach in developing broadband, tunable, as well as switchable AT electromagnetic devices.

Effects of electrical stress on the characteristics and defect behaviors in GaN-based near-ultraviolet light emitting diodes Suggested by editors

Ying-Zhe Wang(王颖哲), Mao-Sen Wang(王茂森), Ning Hua(化宁), Kai Chen(陈凯), Zhi-Min He(何志敏), Xue-Feng Zheng(郑雪峰), Pei-Xian Li(李培咸), Xiao-Hua Ma(马晓华), Li-Xin Guo(郭立新), and Yue Hao(郝跃)

Chin. Phys. B, 2022, 31 (6): 068101. DOI: 10.1088/1674-1056/ac4cb8

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The degradation mechanism of GaN-based near-ultraviolet (NUV, 320-400 nm) light emitting diodes (LEDs) with low-indium content under electrical stress is studied from the aspect of defects. A decrease in the optical power and an increase in the leakage current are observed after electrical stress. The defect behaviors are characterized using deep level transient spectroscopy (DLTS) measurement under different filling pulse widths. After stress, the concentration of defects with the energy level of 0.47-0.56 eV increases, accompanied by decrease in the concentration of 0.72-0.84 eV defects. Combing the defect energy level with the increased yellow luminescence in photoluminescence spectra, the device degradation can be attributed to the activation of the gallium vacancy and oxygen related complex defect along dislocation, which was previously passivated with hydrogen. This study reveals the evolution process of defects under electrical stress and their spatial location, laying a foundation for manufacture of GaN-based NUV LEDs with high reliability.

Multi-phase field simulation of competitive grain growth for directional solidification

Chang-Sheng Zhu(朱昶胜), Zi-Hao Gao(高梓豪), Peng Lei(雷鹏), Li Feng(冯力), and Bo-Rui Zhao(赵博睿)

Chin. Phys. B, 2022, 31 (6): 068102. DOI: 10.1088/1674-1056/ac4486

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The multi-phase field model of grain competitive growth during directional solidification of alloy is established. Solving multi-phase field models for thin interface layer thickness conditions, the grain boundary evolution and grain elimination during the competitive growth of SCN-0.24-wt% camphor model alloy bi-crystals are investigated. The effects of different crystal orientations and pulling velocities on grain boundary microstructure evolution are quantitatively analyzed. The obtained results are shown below. In the competitive growth of convergent bi-crystals, when favorably oriented dendrites are in the same direction as the heat flow and the pulling speed is too large, the orientation angle of the bi-crystal from small to large size is the normal elimination phenomenon of the favorably oriented dendrite, blocking the unfavorably oriented dendrite, and the grain boundary is along the growth direction of the favorably oriented dendrite. When the pulling speed becomes small, the grain boundary shows the anomalous elimination phenomenon of the unfavorably oriented dendrite, eliminating the favorably oriented dendrite. In the process of competitive growth of divergent bi-crystal, when the growth direction of favorably oriented dendrites is the same as the heat flow direction and the orientation angle of unfavorably oriented grains is small, the frequency of new spindles of favorably oriented grains is significantly higher than that of unfavorably oriented grains, and as the orientation angle of unfavorably oriented dendrites becomes larger, the unfavorably oriented grains are more likely to have stable secondary dendritic arms, which in turn develop new primary dendritic arms to occupy the liquid phase grain boundary space, but the grain boundary direction is still parallel to favorably oriented dendrites. In addition, the tertiary dendritic arms on the developed secondary dendritic arms may also be blocked by the surrounding lateral branches from further developing into nascent main axes, this blocking of the tertiary dendritic arms has a random nature, which can have aninfluence on the generation of nascent primary main axes in the grain boundaries.

Synergistic influences of titanium, boron, and oxygen on large-size single-crystal diamond growth at high pressure and high temperature

Guang-Tong Zhou(周广通), Yu-Hu Mu(穆玉虎), Yuan-Wen Song(宋元文), Zhuang-Fei Zhang(张壮飞), Yue-Wen Zhang(张跃文), Wei-Xia Shen(沈维霞), Qian-Qian Wang(王倩倩), Biao Wan(万彪), Chao Fang(房超), Liang-Chao Chen(陈良超), Ya-Dong Li(李亚东), and Xiao-Peng Jia(贾晓鹏)

Chin. Phys. B, 2022, 31 (6): 068103. DOI: 10.1088/1674-1056/ac4650

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The synergistic influences of boron, oxygen, and titanium on growing large single-crystal diamonds are studied using different concentrations of B₂O₃ in a solvent-carbon system under 5.5 GPa-5.7 GPa and 1300 ℃-1500 ℃. It is found that the boron atoms are difficult to enter into the crystal when boron and oxygen impurities are doped using B₂O₃ without the addition of Ti atoms. However, high boron content is achieved in the doped diamonds that were synthesized with the addition of Ti. Additionally, boron-oxygen complexes are found on the surface of the crystal, and oxygen-related impurities appear in the crystal interior when Ti atoms are added into the FeNi-C system. The results show that the introduction of Ti atoms into the synthesis cavity can effectively control the number of boron atoms and the number of oxygen atoms in the crystal. This has important scientific significance not only for understanding the synergistic influence of boron, oxygen, and titanium atoms on the growth of diamond in the earth, but also for preparing the high-concentration boron or oxygen containing semiconductor diamond technologies.

Mg-doped layered oxide cathode for Na-ion batteries Suggested by editors

Yuejun Ding(丁月君), Feixiang Ding(丁飞翔), Xiaohui Rong(容晓晖), Yaxiang Lu(陆雅翔), and Yong-Sheng Hu(胡勇胜)

Chin. Phys. B, 2022, 31 (6): 068201. DOI: 10.1088/1674-1056/ac523b

Abstract ( 475 )

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Na-ion batteries (NIBs) are regarding as the optimum complement for Li-ion batteries along with the rapid development of stationary energy storage systems. In order to meet the commercial demands of cathodes for NIBs, O3-type Cu containing layered oxide Na_0.90Cu_0.22Fe_0.30Mn_0.48O₂ with good comprehensive performance and low-cost element components is very promising for the practical use. However, only part of the Cu³⁺/Cu²⁺ redox couple participated in the redox reaction, thus impairing the specific capacity of the cathode materials. Herein, Mg²⁺-doped O3-Na_0.90Mg_0.08Cu_0.22Fe_0.30Mn_0.40O₂ layered oxide without Mn³⁺ was synthesized successfully, which exhibited improved reversible specific capacity of 118 mAh/g in the voltage range of 2.4-4.0 V at 0.2 C, corresponding to the intercalation/deintercalation of 0.47 Na⁺ (0.1 more than that of Na_0.90Cu_0.22Fe_0.30Mn_0.48O₂). This work demonstrates an important strategy to obtain advanced layered oxide cathodes for NIBs.

A high rectification efficiency Si_0.14Ge_0.72Sn_0.14–Ge_0.82Sn_0.18–Ge quantum structure n-MOSFET for 2.45 GHz weak energy microwave wireless energy transmission

Dong Zhang(张栋), Jianjun Song(宋建军), Xiaohuan Xue(薛笑欢), and Shiqi Zhang(张士琦)

Chin. Phys. B, 2022, 31 (6): 068401. DOI: 10.1088/1674-1056/ac339e

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The design strategy and efficiency optimization of a Ge-based n-type metal-oxide-semiconductor field-effect transistor (n-MOSFET) with a Si_0.14Ge_0.72Sn_0.14-Ge_0.82Sn_0.18-Ge quantum structure used for 2.45 GHz weak energy microwave wireless energy transmission is reported. The quantum structure combined with δ-doping technology is used to reduce the scattering of the device and improve its electron mobility; at the same time, the generation of surface channels is suppressed by the Si_0.14Ge_0.72Sn_0.14 cap layer. By adjusting the threshold voltage of the device to 91 mV, setting the device aspect ratio to 1 μm/0.4 μm and adopting a novel diode connection method, the rectification efficiency of the device is improved. With simulation by Silvaco TCAD software, good performance is displayed in the transfer and output characteristics. For a simple half-wave rectifier circuit with a load of 1 pf and 20 kΩ , the rectification efficiency of the device can reach 7.14% at an input power of -10 dBm, which is 4.2 times that of a Si MOSFET (with a threshold voltage of 80 mV) under the same conditions; this device shows a better rectification effect than a Si MOSFET in the range of -30 dBm to 6.9 dBm.

Simulation design of normally-off AlGaN/GaN high-electron-mobility transistors with p-GaN Schottky hybrid gate

Yun-Long He(何云龙), Fang Zhang(张方), Kai Liu(刘凯), Yue-Hua Hong(洪悦华), Xue-Feng Zheng(郑雪峰),Chong Wang(王冲), Xiao-Hua Ma(马晓华), and Yue Hao(郝跃)

Chin. Phys. B, 2022, 31 (6): 068501. DOI: 10.1088/1674-1056/ac3739

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A novel normally-off AlGaN/GaN high-electron-mobility transistor (HEMT) with a p-GaN Schottky hybrid gate (PSHG) is proposed, and compared with the conventional p-GaN normally-off AlGaN/GaN HEMTs. This structure can be realized by selective etching of p-GaN layer, which enables the Schottky junction and PN junction to control the channel charge at the same time. The direct current (DC) and switching characteristics of the PSHG HEMTs are simulated by Slivaco TCAD, and the p-GaN HEMTs and conventional normally-on HEMTs are also simulated for comparison. The simulation results show that the PSHG HEMTs have a higher current density and a lower on-resistance than p-GaN HEMTs, which is more obvious with the decrease of p-GaN ratios of the PSHG HEMTs. The breakdown voltage and threshold voltage of the PSHG HEMTs are very close to those of the p-GaN HEMTs. In addition, the PSHG HEMTs have a higher switching speed than the conventional normally-on HEMTs, and the p-GaN layer ratio has no obvious effect on the switching speed.

An electromagnetic simulation assisted small signal modeling method for InP double-heterojunction bipolar transistors

Yanzhe Wang(王彦喆), Wuchang Ding(丁武昌), Yongbo Su(苏永波), Feng Yang(杨枫),Jianjun Ding(丁建君), Fugui Zhou(周福贵), and Zhi Jin(金智)

Chin. Phys. B, 2022, 31 (6): 068502. DOI: 10.1088/1674-1056/ac4f55

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We present a convenient and practical electromagnetic (EM) assisted small-signal model extraction method for InP double-heterojunction bipolar transistors (DHBTs). Parasitic parameters of pad and electrode fingers are extracted by means of 3D EM simulation. The simulations with a new excitation scheme are closer to the actual on-wafer measurement conditions. Appropriate simulation settings are calibrated by comparing measurement and simulation of OPEN and SHORT structures. A simpler $\pi $-type topology is proposed for the intrinsic model, in which the base-collector resistance $R_\mu$, output resistance $R_{\rm ce}$ are deleted, and a capacitance $C_{\rm ce}$ is introduced to characterize the capacitive parasitic caused by the collector finger and emitter ground bar. The intrinsic parameters are all extracted by exact equations that are derived from rigorous mathematics. The method is characterized by its ease of implementation and the explicit physical meaning of extraction procedure. Experimental validations are performed at four biases for three InGaAs/InP HBT devices with $0.8\times 7 $μm, 0$.8\times 10 $μm and $0.8\times 15 $μm emitter, and quite good fitting results are obtained in the range of 0.1-50 GHz.

Wet etching and passivation of GaSb-based very long wavelength infrared detectors Suggested by editors

Xue-Yue Xu(许雪月), Jun-Kai Jiang(蒋俊锴), Wei-Qiang Chen(陈伟强), Su-Ning Cui(崔素宁), Wen-Guang Zhou(周文广), Nong Li(李农), Fa-Ran Chang(常发冉), Guo-Wei Wang(王国伟), Ying-Qiang Xu(徐应强), Dong-Wei Jiang(蒋洞微), Dong-Hai Wu(吴东海), Hong-Yue Hao(郝宏玥), and Zhi-Chuan Niu(牛智川)

Chin. Phys. B, 2022, 31 (6): 068503. DOI: 10.1088/1674-1056/ac4cc1

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The etching and passivation processes of very long wavelength infrared (VLWIR) detector based on the InAs/GaSb/AlSb type-II superlattice have been studied. By studying the effect of each component in the citric acid solution (citric acid, phosphoric acid, hydrogen peroxide, deionized water), the best solution ratio is obtained. After comparing different passivation materials such as sulfide + SiO₂, Al₂O₃, Si₃N₄ and SU8, it is found that SU8 passivation can reduce the dark current of the device to a greater degree. Combining this wet etching and SU8 passivation, the R₀A of VLWIR detector with a mesa diameter of 500 μm is about 3.6 Ω ·cm² at 77 K.

Modeling and numerical simulation of electrical and optical characteristics of a quantum dot light-emitting diode based on the hopping mobility model: Influence of quantum dot concentration

Pezhman Sheykholeslami-Nasab, Mahdi Davoudi-Darareh, and Mohammad Hassan Yousefi

Chin. Phys. B, 2022, 31 (6): 068504. DOI: 10.1088/1674-1056/ac364b

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We present a comprehensive numerical framework for the electrical and optical modeling and simulation of hybrid quantum dot light-emitting diodes (QD-LEDs). We propose a model known as hopping mobility to calculate the carrier mobility in the emissive organic layer doped with quantum dots (QDs). To evaluate the ability of this model to describe the electrical characteristics of QD-LEDs, the measured data of a fabricated QD-LED with different concentrations of QDs in the emissive layer were taken, and the corresponding calculations were performed based on the proposed model. The simulation results indicate that the hopping mobility model can describe the concentration dependence of the electrical behavior of the device. Then, based on the continuity equation for singlet and triplet excitons, the exciton density profiles of the devices with different QD concentrations were extracted. Subsequently, the corresponding luminance characteristics of the devices were calculated, where the results are in good agreement with the experimental data.

Spin transport in epitaxial Fe₃O₄/GaAs lateral structured devices Suggested by editors

Zhaocong Huang(黄兆聪), Wenqing Liu(刘文卿), Jian Liang(梁健), Qingjie Guo(郭庆杰), Ya Zhai(翟亚), and Yongbing Xu(徐永兵)

Chin. Phys. B, 2022, 31 (6): 068505. DOI: 10.1088/1674-1056/ac4903

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Research in the spintronics community has been intensively stimulated by the proposal of the spin field-effect transistor (SFET), which has the potential for combining the data storage and process in a single device. Here we report the spin dependent transport on a Fe₃O₄/GaAs based lateral structured device. Parallel and antiparallel states of two Fe₃O₄ electrodes are achieved. A clear MR loop shows the perfect butterfly shape at room temperature, of which the intensity decreases with the reducing current, showing the strong bias dependence. Understanding the spin-dependent transport properties in this architecture has strong implication in further development of the spintronic devices for room-temperature SFETs.

Simulation of the physical process of neural electromagnetic signal generation based on a simple but functional bionic Na⁺ channel

Fan Wang(王帆), Jingjing Xu(徐晶晶), Yanbin Ge(葛彦斌), Shengyong Xu(许胜勇),Yanjun Fu(付琰军), Caiyu Shi(石蔡语), and Jianming Xue(薛建明)

Chin. Phys. B, 2022, 31 (6): 068701. DOI: 10.1088/1674-1056/ac3cac

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The physical processes occurring at open Na⁺ channels in neural fibers are essential for the understanding of the nature of neural signals and the mechanism by which the signals are generated and transmitted along nerves. However, there is a less generally accepted description of these physical processes. We studied changes in the transmembrane ionic flux and the resulting two types of electromagnetic signals by simulating the Na⁺ transport across a bionic nanochannel model simplified from voltage-gated Na⁺ channels. The results show that the Na⁺ flux can reach a steady state in approximately 10 ns due to the dynamic equilibrium of the Na⁺ ion concentration difference between both sides of the membrane. After characterizing the spectrum and transmission of these two electromagnetic signals, the low-frequency transmembrane electric field is regarded as the physical quantity transmitting in the waveguide-like lipid dielectric layer and triggering the neighboring voltage-gated channels. Factors influencing the Na⁺ flux transport are also studied. The impact of the Na⁺ concentration gradient is found to be higher than that of the initial transmembrane potential on the Na⁺ transport rate, and introducing the surface-negative charge in the upper third channel could increase the transmembrane Na⁺ current. This work can be further studied by improving the simulation model; however, the current work helps to better understand the electrical functions of voltage-gated ion channels in neural systems.

Plasmon-induced transparency effect in hybrid terahertz metamaterials with active control and multi-dark modes Suggested by editors

Yuting Zhang(张玉婷), Songyi Liu(刘嵩义), Wei Huang(黄巍), Erxiang Dong(董尔翔), Hongyang Li(李洪阳), Xintong Shi(石欣桐), Meng Liu(刘蒙), Wentao Zhang(张文涛), Shan Yin(银珊), and Zhongyue Luo(罗中岳)

Chin. Phys. B, 2022, 31 (6): 068702. DOI: 10.1088/1674-1056/ac4f56

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We numerically demonstrate a photo-excited plasmon-induced transparency (PIT) effect in hybrid terahertz (THz) metamaterials. The proposed metamaterials are regular arrays of hybrid unit cells composed of a metallic cut wire and four metallic split-ring resonators (SRRs) whose gaps are filled with photosensitive semiconductor gallium arsenide (GaAs) patches. We simulate the PIT effect controlled by external infrared light intensity to change the conductivity of GaAs. In the absence of photo excitation, the conductivity of GaAs is 0, thus the SRR gaps are disconnected, and the PIT effect is not observed since the dark resonator (supported by the hybrid SRRs) cannot be stimulated. When the conductivity of GaAs is increased via photo excitation, the conductivity of GaAs can increase rapidly from 0 S/m to 1×10⁶ S/m and GaAs can connect the metal aluminum SRR gaps, and the dark resonator is excited through coupling with the bright resonator (supported by the cut wire), which leads to the PIT effect. Therefore, the PIT effect can be dynamically tuned between the on and off states by controlling the intensity of the external infrared light. We also discuss couplings between one bright mode (CW) and several dark modes (SRRs) with different sizes. The interference analytically described by the coupled Lorentz oscillator model elucidates the coupling mechanism between one bright mode and two dark modes. The phenomenon can be considered the result of linear superposition of the coupling between the bright mode and each dark mode. The proposed metamaterials are promising for application in the fields of THz communications, optical storage, optical display, and imaging.

Scaled radar cross section measurement method for lossy targets via dynamically matching reflection coefficients in THz band

Shuang Pang(逄爽), Yang Zeng(曾旸), Qi Yang(杨琪), Bin Deng(邓彬), and Hong-Qiang Wang(王宏强)

Chin. Phys. B, 2022, 31 (6): 068703. DOI: 10.1088/1674-1056/ac474b

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In the terahertz band, the dispersive characteristic of dielectric material is one of the major problems in the scaled radar cross section (RCS) measurement, which is inconsistent with the electrodynamics similitude deducted according to the Maxwell's equations. Based on the high-frequency estimation method of physical optics (PO), a scaled RCS measurement method for lossy objects is proposed through dynamically matching the reflection coefficients according to the distribution of the object facets. Simulations of the model of SLICY are conducted, and the inversed RCS of the lossy prototype is obtained using the proposed method. Comparing the inversed RCS with the calculated results, the validity of the proposed method is demonstrated. The proposed method provides an effective solution to the scaled RCS measurement for lossy objects in the THz band.

Force-constant-decayed anisotropic network model: An improved method for predicting RNA flexibility ^Hot!

Wei-Bu Wang(王韦卜), Xing-Yuan Li(李兴元), and Ji-Guo Su(苏计国)

Chin. Phys. B, 2022, 31 (6): 068704. DOI: 10.1088/1674-1056/ac560e

Abstract ( 403 )

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RNA is an important biological macromolecule, which plays an irreplaceable role in many life activities. RNA functions are largely determined by its tertiary structure and the intrinsic dynamics encoded in the structure. Thus, how to effective extract structure-encoded dynamics is of great significance for understanding RNA functions. Anisotropic network model (ANM) is an efficient method to investigate macromolecular dynamical properties, which has been widely used in protein studies. However, the performance of the conventional ANM in describing RNA flexibility is not as good as that on proteins. In this study, we proposed a new approach, named force-constant-decayed anisotropic network model (fcd-ANM), to improve the performance in investigating the dynamical properties encoded in RNA structures. In fcd-ANM, nucleotide pairs in RNA structure were connected by springs and the force constant of springs was decayed exponentially based on the separation distance to describe the differences in the inter-nucleotide interaction strength. The performance of fcd-ANM in predicting RNA flexibility was evaluated using a non-redundant structure database composed of 51 RNAs. The results indicate that fcd-ANM significantly outperforms the conventional ANM in reproducing the experimental B-factors of nucleotides in RNA structures, and the Pearson correlation coefficient between the predicted and experimental nucleotide B-factors was distinctly improved by 21.05% compared to the conventional ANM. Fcd-ANM can serve as a more effective method for analysis of RNA dynamical properties.

Influence fast or later: Two types of influencers in social networks

Fang Zhou(周方), Chang Su(苏畅), Shuqi Xu(徐舒琪), and Linyuan Lü(吕琳媛)

Chin. Phys. B, 2022, 31 (6): 068901. DOI: 10.1088/1674-1056/ac4484

Abstract ( 457 )

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In real-world networks, there usually exist a small set of nodes that play an important role in the structure and function of networks. Those vital nodes can influence most of other nodes in the network via a spreading process. While most of the existing works focused on vital nodes that can maximize the spreading size in the final stage, which we call final influencers, recent work proposed the idea of fast influencers, which emphasizes nodes' spreading capacity at the early stage. Despite the recent surge of efforts in identifying these two types of influencers in networks, there remained limited research on untangling the differences between the fast influencers and final influencers. In this paper, we firstly distinguish the two types of influencers: fast-only influencers and final-only influencers. The former is defined as individuals who can achieve a high spreading effect at the early stage but lose their superiority in the final stage, and the latter are those individuals that fail to exhibit a prominent spreading performance at the early stage but influence a large fraction of nodes at the final stage. Further experiments are based on eight empirical datasets, and we reveal the key differences between the two types of influencers concerning their spreading capacity and the local structures. We also analyze how network degree assortativity influences the fraction of the proposed two types of influencers. The results demonstrate that with the increase of degree assortativity, the fraction of the fast-only influencers decreases, which indicates that more fast influencers tend to keep their superiority at the final stage. Our study provides insights into the differences and evolution of different types of influencers and has important implications for various empirical applications, such as advertisement marketing and epidemic suppressing.

A novel similarity measure for mining missing links in long-path networks

Yijun Ran(冉义军), Tianyu Liu(刘天宇), Tao Jia(贾韬), and Xiao-Ke Xu(许小可)

Chin. Phys. B, 2022, 31 (6): 068902. DOI: 10.1088/1674-1056/ac4483

Abstract ( 701 )

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Network information mining is the study of the network topology, which may answer a large number of application-based questions towards the structural evolution and the function of a real system. The question can be related to how the real system evolves or how individuals interact with each other in social networks. Although the evolution of the real system may seem to be found regularly, capturing patterns on the whole process of evolution is not trivial. Link prediction is one of the most important technologies in network information mining, which can help us understand the evolution mechanism of real-life network. Link prediction aims to uncover missing links or quantify the likelihood of the emergence of nonexistent links from known network structures. Currently, widely existing methods of link prediction almost focus on short-path networks that usually have a myriad of close triangular structures. However, these algorithms on highly sparse or long-path networks have poor performance. Here, we propose a new index that is associated with the principles of structural equivalence and shortest path length (SESPL) to estimate the likelihood of link existence in long-path networks. Through a test of 548 real networks, we find that SESPL is more effective and efficient than other similarity-based predictors in long-path networks. Meanwhile, we also exploit the performance of SESPL predictor and of embedding-based approaches via machine learning techniques. The results show that the performance of SESPL can achieve a gain of 44.09% over GraphWave and 7.93% over Node2vec. Finally, according to the matrix of maximal information coefficient (MIC) between all the similarity-based predictors, SESPL is a new independent feature in the space of traditional similarity features.

Advantage of populous countries in the trends of innovation efficiency

Dan-Dan Hu(胡淡淡), Xue-Jin Fang(方学进), and Xiao-Pu Han(韩筱璞)

Chin. Phys. B, 2022, 31 (6): 068903. DOI: 10.1088/1674-1056/ac5614

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A flurry of studies indicates that population size has a positive effect on innovation, however, cross-country empirical evidence remains sparse. In this paper, we add to the literature by investigating the relationship between population size and innovation efficiency at the country level through constructing three relative indexes based on the datasets of patent applications and Research and Development (R&D) investment. Different from previous studies based on absolute innovation indicators, the relative indexes can reflect the core innovation efficiency of economies by excluding the impact from the difference of economic development level, with a view putting all economies into a comparable standard framework. For all of the three relative indexes, their long-term trends show significant correlations with population size, and the economy with a larger population usually has better and stable performance on the trends of innovation efficiency. In addition, we find that there is a critical population size, over which the economy would be more likely to have a spontaneous improvement on innovation efficiency. This study provides direct evidence in supporting the population size advantage on the trends of innovation efficiency at the economy level and provides new insight to understand the rapid development of innovation in a few populous countries.

An extended improved global structure model for influential node identification in complex networks

Jing-Cheng Zhu(朱敬成) and Lun-Wen Wang(王伦文)

Chin. Phys. B, 2022, 31 (6): 068904. DOI: 10.1088/1674-1056/ac380d

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Accurate identification of influential nodes facilitates the control of rumor propagation and interrupts the spread of computer viruses. Many classical approaches have been proposed by researchers regarding different aspects. To explore the impact of location information in depth, this paper proposes an improved global structure model to characterize the influence of nodes. The method considers both the node's self-information and the role of the location information of neighboring nodes. First, degree centrality of each node is calculated, and then degree value of each node is used to represent self-influence, and degree values of the neighbor layer nodes are divided by the power of the path length, which is path attenuation used to represent global influence. Finally, an extended improved global structure model that considers the nearest neighbor information after combining self-influence and global influence is proposed to identify influential nodes. In this paper, the propagation process of a real network is obtained by simulation with the SIR model, and the effectiveness of the proposed method is verified from two aspects of discrimination and accuracy. The experimental results show that the proposed method is more accurate in identifying influential nodes than other comparative methods with multiple networks.

Analysis of identification methods of key nodes in transportation network Suggested by editors

Qiang Lai(赖强) and Hong-Hao Zhang(张宏昊)

Chin. Phys. B, 2022, 31 (6): 068905. DOI: 10.1088/1674-1056/ac4a6c

Abstract ( 430 )

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The identification of key nodes plays an important role in improving the robustness of the transportation network. For different types of transportation networks, the effect of the same identification method may be different. It is of practical significance to study the key nodes identification methods corresponding to various types of transportation networks. Based on the knowledge of complex networks, the metro networks and the bus networks are selected as the objects, and the key nodes are identified by the node degree identification method, the neighbor node degree identification method, the weighted k-shell degree neighborhood identification method (KSD), the degree k-shell identification method (DKS), and the degree k-shell neighborhood identification method (DKSN). Take the network efficiency and the largest connected subgraph as the effective indicators. The results show that the KSD identification method that comprehensively considers the elements has the best recognition effect and has certain practical significance.

Effects of heterogeneous adoption thresholds on contact-limited social contagions

Dan-Dan Zhao(赵丹丹), Wang-Xin Peng(彭王鑫), Hao Peng(彭浩), and Wei Wang(王伟)

Chin. Phys. B, 2022, 31 (6): 068906. DOI: 10.1088/1674-1056/ac4e04

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Limited contact capacity and heterogeneous adoption thresholds have been proven to be two essential characteristics of individuals in natural complex social systems, and their impacts on social contagions exhibit complex nature. With this in mind, a heterogeneous contact-limited threshold model is proposed, which adopts one of four threshold distributions, namely Gaussian distribution, log-normal distribution, exponential distribution and power-law distribution. The heterogeneous edge-based compartmental theory is developed for theoretical analysis, and the calculation methods of the final adoption size and outbreak threshold are given theoretically. Many numerical simulations are performed on the Erdös-Rényi and scale-free networks to study the impact of different forms of the threshold distribution on hierarchical spreading process, the final adoption size, the outbreak threshold and the phase transition in contact-limited propagation networks. We find that the spreading process of social contagions is divided into three distinct stages. Moreover, different threshold distributions cause different spreading processes, especially for some threshold distributions, there is a change from a discontinuous first-order phase transition to a continuous second-order phase transition. Further, we find that changing the standard deviation of different threshold distributions will cause the final adoption size and outbreak threshold to change, and finally tend to be stable with the increase of standard deviation.

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