Chin. Phys. B

Bifurcation and dynamics in double-delayed Chua circuits with periodic perturbation

Wenjie Yang(杨文杰)

Chin. Phys. B, 2022, 31 (2): 020201. DOI: 10.1088/1674-1056/ac1e0b

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Rank-1 attractors play a vital role in biological systems and the circuit systems. In this paper, we consider a periodically kicked Chua model with two delays in a circuit system. We first analyze the local stability of the equilibria of the Chua system and obtain the existence conditions of supercritical Hopf bifurcations. Then, we derive some explicit formulas about Hopf bifurcation, which could help us find the form of Hopf bifurcation and the stability of bifurcating period solutions through the Hassards method. Also, we show that rank-1 chaos occurs when the Chua model with two delays undergoes a supercritical Hopf bifurcation and encounters a periodic kick, which shows the effect of two delays on the circuit system. Finally, we illustrate the theoretical analysis by simulations and try to explain the mechanism of delay in our system.

Stochastic optimal control for norovirus transmission dynamics by contaminated food and water Suggested by editors

Anwarud Din and Yongjin Li(黎永锦)

Chin. Phys. B, 2022, 31 (2): 020202. DOI: 10.1088/1674-1056/ac2f32

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Norovirus is one of the most common causes of viral gastroenteritis in the world, causing significant morbidity, deaths, and medical costs. In this work, we look at stochastic modelling methodologies for norovirus transmission by water, human to human transmission and food. To begin, the proposed stochastic model is shown to have a single global positive solution. Second, we demonstrate adequate criteria for the existence of a unique ergodic stationary distribution $\mathfrak{R_s^0}>1$ by developing a Lyapunov function. Thirdly, we find sufficient criteria $\mathfrak{R_s}<1$ for disease extinction. Finally, two simulation examples are used to exemplify the analytical results. We employed optimal control theory and examined stochastic control problems to regulate the spread of the disease using some external measures. Additional graphical solutions have been produced to further verify the acquired analytical results. This research could give a solid theoretical foundation for understanding chronic communicable diseases around the world. Our approach also focuses on offering a way of generating Lyapunov functions that can be utilized to investigate the stationary distribution of epidemic models with nonlinear stochastic disturbances.

Memory-augmented adaptive flocking control for multi-agent systems subject to uncertain external disturbances

Ximing Wang(王希铭), Jinsheng Sun(孙金生), Zhitao Li(李志韬), and Zixing Wu(吴梓杏)

Chin. Phys. B, 2022, 31 (2): 020203. DOI: 10.1088/1674-1056/ac21c1

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This paper presents a novel flocking algorithm based on a memory-enhanced disturbance observer. To compensate for external disturbances, a filtered regressor for the double integrator model subject to external disturbances is designed to extract the disturbance information. With the filtered regressor method, the algorithm has the advantage of eliminating the need for acceleration information, thus reducing the sensor requirements in applications. Using the information obtained from the filtered regressor, a batch of stored data is used to design an adaptive disturbance observer, ensuring that the estimated values of the parameters of the disturbance system equation and the initial value converge to their actual values. The result is that the flocking algorithm can compensate for external disturbances and drive agents to achieve the desired collective behavior, including virtual leader tracking, inter-distance keeping, and collision avoidance. Numerical simulations verify the effectiveness of the algorithm proposed in the present study.

Time evolution law of a two-mode squeezed light field passing through twin diffusion channels

Hai-Jun Yu(余海军) and Hong-Yi Fan(范洪义)

Chin. Phys. B, 2022, 31 (2): 020301. DOI: 10.1088/1674-1056/ac140b

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We explore the time evolution law of a two-mode squeezed light field (pure state) passing through twin diffusion channels, and we find that the final state is a squeezed chaotic light field (mixed state) with entanglement, which shows that even though the two channels are independent of each other, since the two modes of the initial state are entangled with each other, the final state remains entangled. Nevertheless, although the squeezing (entanglement) between the two modes is weakened after the diffusion, it is not completely removed. We also highlight the law of photon number evolution. In the calculation process used in this paper, we make full use of the summation method within the ordered product of operators and the generating function formula for two-variable Hermite polynomials.

Channel parameters-independent multi-hop nondestructive teleportation

Hua-Yang Li(李华阳), Yu-Zhen Wei(魏玉震), Yi Ding(丁祎), and Min Jiang(姜敏)

Chin. Phys. B, 2022, 31 (2): 020302. DOI: 10.1088/1674-1056/ac1330

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A multi-hop nondestructive teleportation scheme independent of channel parameters based on Bell pairs is presented, where the coefficients of the quantum channel are unknown to all the communication nodes. With Bell measurement and channel matching technology the unknown channel parameters can be eliminated probabilistically with the help of the intermediate nodes. Then the source node Alice can teleport an unknown state to the remote destination node Bob. In our scheme the teleportation is generalized first to the scenario independent of channel parameters, which makes the requirement of quantum channel reduced. Our scheme still preserves the initial unknown state even if this teleportation fails. Moreover, performance analysis shows that our scheme has a higher communication efficiency.

Optical wavelet-fractional squeezing combinatorial transform

Cui-Hong Lv(吕翠红), Ying Cai(蔡莹), Nan Jin(晋楠), and Nan Huang(黄楠)

Chin. Phys. B, 2022, 31 (2): 020303. DOI: 10.1088/1674-1056/ac1e1c

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By virtue of the method of integration within ordered product (IWOP) of operators we find the normally ordered form of the optical wavelet-fractional squeezing combinatorial transform (WFrST) operator. The way we successfully combine them to realize the integration transform kernel of WFrST is making full use of the completeness relation of Dirac's ket-bra representation. The WFrST can play role in analyzing and recognizing quantum states, for instance, we apply this new transform to identify the vacuum state, the single-particle state, and their superposition state.

Quantum simulation of lattice gauge theories on superconducting circuits: Quantum phase transition and quench dynamics Suggested by editors

Zi-Yong Ge(葛自勇), Rui-Zhen Huang(黄瑞珍), Zi-Yang Meng(孟子杨), and Heng Fan(范桁)

Chin. Phys. B, 2022, 31 (2): 020304. DOI: 10.1088/1674-1056/ac380e

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Recently, quantum simulation of low-dimensional lattice gauge theories (LGTs) has attracted many interests, which may improve our understanding of strongly correlated quantum many-body systems. Here, we propose an implementation to approximate $\mathbb{Z}_2$ LGT on superconducting quantum circuits, where the effective theory is a mixture of a LGT and a gauge-broken term. By using matrix product state based methods, both the ground state properties and quench dynamics are systematically investigated. With an increase of the transverse (electric) field, the system displays a quantum phase transition from a disordered phase to a translational symmetry breaking phase. In the ordered phase, an approximate Gauss law of the $\mathbb{Z}_2$ LGT emerges in the ground state. Moreover, to shed light on the experiments, we also study the quench dynamics, where there is a dynamical signature of the spontaneous translational symmetry breaking. The spreading of the single particle of matter degree is diffusive under the weak transverse field, while it is ballistic with small velocity for the strong field. Furthermore, due to the emergent Gauss law under the strong transverse field, the matter degree can also exhibit confinement dynamics which leads to a strong suppression of the nearest-neighbor hopping. Our results pave the way for simulating the LGT on superconducting circuits, including the quantum phase transition and quench dynamics.

Change-over switch for quantum states transfer with topological channels in a circuit-QED lattice Suggested by editors

Liu-Yong Cheng(程留永), Li-Na Zheng(郑黎娜), Ruixiang Wu(吴瑞祥), Hong-Fu Wang(王洪福), and Shou Zhang(张寿)

Chin. Phys. B, 2022, 31 (2): 020305. DOI: 10.1088/1674-1056/ac2f2e

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We propose schemes to realize robust quantum states transfer between distant resonators using the topological edge states of a one-dimensional circuit quantum electrodynamics (QED) lattice. Analyses show that the distribution of edge states can be regulated accordingly with the on-site defects added on the resonators. And we can achieve different types of quantum state transfer without adjusting the number of lattices. Numerical simulations demonstrate that the on-site defects can be used as a change-over switch for high-fidelity single-qubit and two-qubit quantum states transfer. This work provides a viable prospect for flexible quantum state transfer in solid-state topological quantum system.

Parameter estimation of continuous variable quantum key distribution system via artificial neural networks Suggested by editors

Hao Luo(罗浩), Yi-Jun Wang(王一军), Wei Ye(叶炜), Hai Zhong(钟海), Yi-Yu Mao(毛宜钰), and Ying Guo(郭迎)

Chin. Phys. B, 2022, 31 (2): 020306. DOI: 10.1088/1674-1056/ac2807

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Continuous-variable quantum key distribution (CVQKD) allows legitimate parties to extract and exchange secret keys. However, the tradeoff between the secret key rate and the accuracy of parameter estimation still around the present CVQKD system. In this paper, we suggest an approach for parameter estimation of the CVQKD system via artificial neural networks (ANN), which can be merged in post-processing with less additional devices. The ANN-based training scheme, enables key prediction without exposing any raw key. Experimental results show that the error between the predicted values and the true ones is in a reasonable range. The CVQKD system can be improved in terms of the secret key rate and the parameter estimation, which involves less additional devices than the traditional CVQKD system.

Darboux transformation and soliton solutions of a nonlocal Hirota equation

Yarong Xia(夏亚荣), Ruoxia Yao(姚若侠), and Xiangpeng Xin(辛祥鹏)

Chin. Phys. B, 2022, 31 (2): 020401. DOI: 10.1088/1674-1056/ac11e9

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Starting from local coupled Hirota equations, we provide a reverse space-time nonlocal Hirota equation by the symmetry reduction method known as the Ablowitz-Kaup-Newell-Segur scattering problem. The Lax integrability of the nonlocal Hirota equation is also guaranteed by existence of the Lax pair. By Lax pair, an n-fold Darboux transformation is constructed for the nonlocal Hirota equation by which some types of exact solutions are found. The solutions with specific properties are distinct from those of the local Hirota equation. In order to further describe the properties and the dynamic features of the solutions explicitly, several kinds of graphs are depicted.

Soliton fusion and fission for the high-order coupled nonlinear Schrödinger system in fiber lasers Suggested by editors

Tian-Yi Wang(王天一), Qin Zhou(周勤), and Wen-Jun Liu(刘文军)

Chin. Phys. B, 2022, 31 (2): 020501. DOI: 10.1088/1674-1056/ac2d22

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With the rapid development of communication technology, optical fiber communication has become a key research area in communications. When there are two signals in the optical fiber, the transmission of them can be abstracted as a high-order coupled nonlinear Schrödinger system. In this paper, by using the Hirota's method, we construct the bilinear forms, and study the analytical solution of three solitons in the case of focusing interactions. In addition, by adjusting different wave numbers for phase control, we further discuss the influence of wave numbers on soliton transmissions. It is verified that wave numbers k₁₁, k₂₁, k₃₁, k₂₂, and k₃₂ can control the fusion and fission of solitons. The results are beneficial to the study of all-optical switches and fiber lasers in nonlinear optics.

Complex dynamic behaviors in hyperbolic-type memristor-based cellular neural network

Ai-Xue Qi(齐爱学), Bin-Da Zhu(朱斌达), and Guang-Yi Wang(王光义)

Chin. Phys. B, 2022, 31 (2): 020502. DOI: 10.1088/1674-1056/ac2b1b

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This paper presents a new hyperbolic-type memristor model, whose frequency-dependent pinched hysteresis loops and equivalent circuit are tested by numerical simulations and analog integrated operational amplifier circuits. Based on the hyperbolic-type memristor model, we design a cellular neural network (CNN) with 3-neurons, whose characteristics are analyzed by bifurcations, basins of attraction, complexity analysis, and circuit simulations. We find that the memristive CNN can exhibit some complex dynamic behaviors, including multi-equilibrium points, state-dependent bifurcations, various coexisting chaotic and periodic attractors, and offset of the positions of attractors. By calculating the complexity of the memristor-based CNN system through the spectral entropy (SE) analysis, it can be seen that the complexity curve is consistent with the Lyapunov exponent spectrum, i.e., when the system is in the chaotic state, its SE complexity is higher, while when the system is in the periodic state, its SE complexity is lower. Finally, the realizability and chaotic characteristics of the memristive CNN system are verified by an analog circuit simulation experiment.

Robust H_∞ state estimation for a class of complex networks with dynamic event-triggered scheme against hybrid attacks

Yahan Deng(邓雅瀚), Zhongkai Mo(莫中凯), and Hongqian Lu(陆宏谦)

Chin. Phys. B, 2022, 31 (2): 020503. DOI: 10.1088/1674-1056/ac0ee9

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We investigate the dynamic event-triggered state estimation for uncertain complex networks with hybrid delays suffering from both deception attacks and denial-of-service attacks. Firstly, the effects of time-varying delays and finite-distributed delays are considered during data transmission between nodes. Secondly, a dynamic event-triggered scheme (ETS) is introduced to reduce the frequency of data transmission between sensors and estimators. Thirdly, by considering the discussed plant, dynamic ETS, state estimator, and hybrid attacks into a unified framework, this framework is transferred into a novel dynamical model. Furthermore, with the help of Lyapunov stability theory and linear matrix inequality techniques, sufficient condition to ensure that the system is exponentially stable and satisfies H_∞ performance constraints is obtained, and the design algorithm for estimator gains is given. Finally, two numerical examples verify the effectiveness of the proposed method.

Explosive synchronization: From synthetic to real-world networks

Atiyeh Bayani, Sajad Jafari, and Hamed Azarnoush

Chin. Phys. B, 2022, 31 (2): 020504. DOI: 10.1088/1674-1056/ac3cb0

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Synchronization is a widespread phenomenon in both synthetic and real-world networks. This collective behavior of simple and complex systems has been attracting much research during the last decades. Two different routes to synchrony are defined in networks; first-order, characterized as explosive, and second-order, characterized as continuous transition. Although pioneer researches explained that the transition type is a generic feature in the networks, recent studies proposed some frameworks in which different phase and even chaotic oscillators exhibit explosive synchronization. The relationship between the structural properties of the network and the dynamical features of the oscillators is mainly proclaimed because some of these frameworks show abrupt transitions. Despite different theoretical analyses about the appearance of the first-order transition, studies are limited to the mean-field theory, which cannot be generalized to all networks. There are different real-world and man-made networks whose properties can be characterized in terms of explosive synchronization, e.g., the transition from unconsciousness to wakefulness in the brain and spontaneous synchronization of power-grid networks. In this review article, explosive synchronization is discussed from two main aspects. First, pioneer articles are categorized from the dynamical-structural framework point of view. Then, articles that considered different oscillators in the explosive synchronization frameworks are studied. In this article, the main focus is on the explosive synchronization in networks with chaotic and neuronal oscillators. Also, efforts have been made to consider the recent articles which proposed new frameworks of explosive synchronization.

FPGA implementation and image encryption application of a new PRNG based on a memristive Hopfield neural network with a special activation gradient

Fei Yu(余飞), Zinan Zhang(张梓楠), Hui Shen(沈辉), Yuanyuan Huang(黄园媛), Shuo Cai(蔡烁), and Sichun Du(杜四春)

Chin. Phys. B, 2022, 31 (2): 020505. DOI: 10.1088/1674-1056/ac3cb2

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A memristive Hopfield neural network (MHNN) with a special activation gradient is proposed by adding a suitable memristor to the Hopfield neural network (HNN) with a special activation gradient. The MHNN is simulated and dynamically analyzed, and implemented on FPGA. Then, a new pseudo-random number generator (PRNG) based on MHNN is proposed. The post-processing unit of the PRNG is composed of nonlinear post-processor and XOR calculator, which effectively ensures the randomness of PRNG. The experiments in this paper comply with the IEEE 754-1985 high precision 32-bit floating point standard and are done on the Vivado design tool using a Xilinx XC7Z020CLG400-2 FPGA chip and the Verilog-HDL hardware programming language. The random sequence generated by the PRNG proposed in this paper has passed the NIST SP800-22 test suite and security analysis, proving its randomness and high performance. Finally, an image encryption system based on PRNG is proposed and implemented on FPGA, which proves the value of the image encryption system in the field of data encryption connected to the Internet of Things (IoT).

Energy spreading, equipartition, and chaos in lattices with non-central forces

Arnold Ngapasare, Georgios Theocharis, Olivier Richoux, Vassos Achilleos, and Charalampos Skokos

Chin. Phys. B, 2022, 31 (2): 020506. DOI: 10.1088/1674-1056/ac3a5e

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We numerically study a one-dimensional, nonlinear lattice model which in the linear limit is relevant to the study of bending (flexural) waves. In contrast with the classic one-dimensional mass-spring system, the linear dispersion relation of the considered model has different characteristics in the low frequency limit. By introducing disorder in the masses of the lattice particles, we investigate how different nonlinearities in the potential (cubic, quadratic, and their combination) lead to energy delocalization, equipartition, and chaotic dynamics. We excite the lattice using single site initial momentum excitations corresponding to a strongly localized linear mode and increase the initial energy of excitation. Beyond a certain energy threshold, when the cubic nonlinearity is present, the system is found to reach energy equipartition and total delocalization. On the other hand, when only the quartic nonlinearity is activated, the system remains localized and away from equipartition at least for the energies and evolution times considered here. However, for large enough energies for all types of nonlinearities we observe chaos. This chaotic behavior is combined with energy delocalization when cubic nonlinearities are present, while the appearance of only quadratic nonlinearity leads to energy localization. Our results reveal a rich dynamical behavior and show differences with the relevant Fermi-Pasta-Ulam-Tsingou model. Our findings pave the way for the study of models relevant to bending (flexural) waves in the presence of nonlinearity and disorder, anticipating different energy transport behaviors.

X-ray focusing using an x-ray lens composed of multi-square polycapillary slices Suggested by editors

Kai Pan(潘凯), Tian-Cheng Yi(易天成), Zhao Wang(王瞾), Mo Zhou(周末), Yu-De Li(李玉德), Zhi-Guo Liu(刘志国), Xiao-Yan Lin(林晓燕), and Tian-Xi Sun(孙天希)

Chin. Phys. B, 2022, 31 (2): 020701. DOI: 10.1088/1674-1056/ac381a

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A new type of x-ray lens composed of multi-square polycapillary slices (ASPXRL) used in focusing parallel x-ray beam was presented in this paper. Compared with conventional x-ray polycapillary lens, ASPXRL can provide smaller and brighter focus. The effects of the manufacturing imperfections on focusing quality of ASPXRL were evaluated with the values of transmission efficiency and discussed. It is suggested that ASPXRL has application prospects as a condenser lens for x-ray microscopy and flux collectors for x-ray analytical instruments.

Generation of laser-driven flyer dominated by shock-induced shear bands: A molecular dynamics simulation study

Deshen Geng(耿德珅), Danyang Liu(刘丹阳), Jianying Lu(鲁建英), Chao Chen(陈超), Junying Wu(伍俊英), Shuzhou Li(李述周), and Lang Chen(陈朗)

Chin. Phys. B, 2022, 31 (2): 024101. DOI: 10.1088/1674-1056/ac2f2d

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High-power pulsed lasers provide an ingenious method for launching metal foils to generate high-speed flyers for high-pressure loading in material science or aerospace engineering. At high-temperature and high-pressure laser-induced conditions, the dynamic response of the metals and the mechanism of flyer formation remain unclear. In this study, the overall process of the laser-driven aluminum flyer, including laser ablation, rupture of metal foil, and the generation of the flyer was investigated by molecular dynamics combined with the two-temperature model. It was found that under high laser fluence (over 1.3 J/cm² with 200-fs laser pulse duration), the laser induced a shock wave with a peak pressure higher than 25 GPa, which led to shear bands expanding from the edge of the laser ablation zone in the foil. Compared with the cases of low laser fluence less than 0.5 J/cm², the shear band induced by high laser fluence promotes the rupture of the foil and results in a high-speed flyer (> 1 km/s) with better flatness and integrity. In addition, the shock wavefront was found to be accompanied by aluminum crystal phase transformation from face-centered cubic (FCC) to body-centered cubic structure. The crystal structure reverts with the decrease of pressure, therefore the internal structure of the generated flyer is pure of FCC. The results of this study provide a better understanding of the laser-induced shock effect on the foil rupture and flyer quality and forward the development of the laser-driven flyer.

Estimation of co-channel interference between cities caused by ducting and turbulence

Kai Yang(杨凯), Zhensen Wu(吴振森), Xing Guo(郭兴), Jiaji Wu(吴家骥), Yunhua Cao(曹运华), Tan Qu(屈檀), and Jiyu Xue(薛积禹)

Chin. Phys. B, 2022, 31 (2): 024102. DOI: 10.1088/1674-1056/ac339c

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With the rapid development of the fifth-generation (5G) mobile communication technology, the application of each frequency band has reached the extreme, causing mutual interference between different modules. Hence, there is a requirement for detecting filtering and preventing interference. In the troposphere, over-the-horizon propagation occurs in atmospheric ducts and turbulent media. The effects of both ducting and turbulence can increase the probability of occurrence of long-distance co-channel interference (CCI), in turn, severely affecting the key performance indicators such as system access, handover and drop. In the 5G era, to ensure communication channels and information security, CCI must be reduced. This paper introduces a scattering parabolic equation algorithm for calculating signal propagation in atmospheric ducts on irregular terrain boundaries. It combines Hitney's radio physical optical model and Wagner's nonuniform turbulent scattering model for calculating the tropospheric scattering in an evaporation duct or a surface-based duct. The new model proposes a tropospheric scattering parabolic equation algorithm for various tropospheric duct environments. Finally, as a specific case, the topographical boundaries between several cities in the East China Plain were considered, and the over-the-horizon propagation loss was simulated for various ducting and turbulent environments. The simulation results were used to evaluate whether CCI would occur between cities in a specific environment.

Determine the physical mechanism and source region of beat wave modulation by changing the frequency of high-frequency waves

Zhe Guo(郭哲), Hanxian Fang(方涵先), and Farideh Honary

Chin. Phys. B, 2022, 31 (2): 024103. DOI: 10.1088/1674-1056/ac422f

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This paper introduces a new approach for the determination of the source region of beat wave (BW) modulation. This type of modulation is achieved by transmitting high-frequency (HF) continuous waves with a frequency difference f, where f is the frequency of modulated ELF/VLF (extremely low frequency/very low frequency) waves from two sub-arrays of a high power HF transmitter. Despite the advantages of BW modulation in terms of generating more stable ELF/VLF signal and high modulation efficiency, there exists a controversy on the physical mechanism of BW and its source region. In this paper, the two controversial theories, i.e., BW based on D-E region thermal nonlinearity and BW based on F region ponderomotive nonlinearity are examined for cases where each of these two theories exists exclusively or both of them exist simultaneously. According to the analysis and simulation results presented in this paper, it is found that the generated VLF signal amplitude exhibits significant variation as a function of HF frequency in different source regions. Therefore, this characteristic can be utilized as a potential new approach to determine the physical mechanism and source location of BW.

An analytical model for cross-Kerr nonlinearity in a four-level N-type atomic system with Doppler broadening

Dinh Xuan Khoa, Nguyen Huy Bang, Nguyen Le Thuy An, Nguyen Van Phu, and Le Van Doai

Chin. Phys. B, 2022, 31 (2): 024201. DOI: 10.1088/1674-1056/ac2d19

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We present an analytical model for cross-Kerr nonlinear coefficient in a four-level N-type atomic medium under Doppler broadening. The model is applied to ⁸⁷Rb atoms to analyze the dependence of the cross-Kerr nonlinear coefficient on the external light field and the temperature of atomic vapor. The analysis shows that in the absence of electromagnetically induced transparency (EIT) the cross-Kerr nonlinear coefficient is zero, but it is significantly enhanced when the EIT is established. It means that the cross-Kerr effect can be turned on/off when the external light field is on or off. Simultaneously, the amplitude and the sign of the cross-Kerr nonlinear coefficient are easily changed according to the intensity and frequency of the external light field. The amplitude of the cross-Kerr nonlinear coefficient remarkably decreases when the temperature of atomic medium increases. The analytical model can be convenient to fit experimental observations and applied to photonic devices.

High-fidelity resonant tunneling passage in three-waveguide system

Rui-Qiong Ma(马瑞琼), Jian Shi(时坚), Lin Liu(刘琳), Meng Liang(梁猛), Zuo-Liang Duan(段作梁), Wei Gao(高伟), and Jun Dong(董军)

Chin. Phys. B, 2022, 31 (2): 024202. DOI: 10.1088/1674-1056/ac0cd4

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An N-stage three-waveguide system is proposed to improve the robustness and the fidelity of the resonant tunneling passage. The analytic solutions to the tunneling dynamics at the output are derived. When the number of subsystems increases, tunneling efficiency approaches to 100% in a large range and resonant tunneling is robust against variations in the phase mismatch and peak tunneling rate.

High efficiency, small size, and large bandwidth vertical interlayer waveguide coupler

Shao-Yang Li(李绍洋), Liang-Liang Wang(王亮亮), Dan Wu(吴丹), Jin You(游金), Yue Wang(王玥), Jia-Shun Zhang(张家顺), Xiao-Jie Yin(尹小杰), Jun-Ming An(安俊明), and Yuan-Da Wu(吴远大)

Chin. Phys. B, 2022, 31 (2): 024203. DOI: 10.1088/1674-1056/ac0dac

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Since the advent of three-dimensional photonic integrated circuits, the realization of efficient and compact optical interconnection between layers has become an important development direction. A vertical interlayer coupler between two silicon layers is presented in this paper. The coupling principle of the directional coupler is analyzed, and the traditional method of using a pair of vertically overlapping inverse taper structures is improved. For the coupling of two rectangular waveguide layers, a pair of nonlinear tapers with offset along the transmission direction is demonstrated. For the coupling of two ridge waveguide layers, a nonlinear taper in each layer is used to achieve high coupling efficiency. The simulation results show that the coupling efficiency of the two structures can reach more than 90% in a wavelength range from 1500 nm to 1650 nm. Moreover, the crosstalk is reduced to less than -50 dB by using multimode waveguides at intersections. The vertical interlayer coupler with a nonlinear taper is expected to realize the miniaturization and dense integration of photonic integrated chips.

High-sensitive terahertz detection by parametric up-conversion using nanosecond pulsed laser Suggested by editors

Yuye Wang(王与烨), Gang Nie(聂港), Changhao Hu(胡常灏), Kai Chen(陈锴), Chao Yan(闫超), Bin Wu(吴斌), Junfeng Zhu(朱军峰), Degang Xu(徐德刚), and Jianquan Yao(姚建铨)

Chin. Phys. B, 2022, 31 (2): 024204. DOI: 10.1088/1674-1056/ac2d20

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A high-sensitive terahertz detector operating at room temperature was demonstrated based on parametric up-conversion. A nanosecond 1064-nm Nd:YAG laser was used to pump the parametric up-conversion detector and the up-conversion from terahertz wave to NIR laser was realized in a lithium niobate crystal. The minimum detectable terahertz energy of 9 pJ was realized with the detection dynamic range of 54 dB, which was three orders of magnitude higher than that of commercial Golay cell. The detectable terahertz frequency range of the detection system was 0.90 Thz-1.83 THz. Besides, the effects of pump energy and effective gain length on the detection sensitivity were studied in experiment. The results showed that higher pump energy and longer effective gain length are helpful for improving the detection sensitivity of parametric up-conversion detector.

A broadband self-powered UV photodetector of a β-Ga₂O₃/γ-CuI p-n junction Suggested by editors

Wei-Ming Sun(孙伟铭), Bing-Yang Sun(孙兵阳), Shan Li(李山), Guo-Liang Ma(麻国梁), Ang Gao(高昂), Wei-Yu Jiang(江为宇), Mao-Lin Zhang(张茂林), Pei-Gang Li(李培刚), Zeng Liu(刘增), and Wei-Hua Tang(唐为华)

Chin. Phys. B, 2022, 31 (2): 024205. DOI: 10.1088/1674-1056/ac29b3

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The symmetric Ti/Au bi-layer point electrodes have been successfully patterned on the β-Ga₂O₃ films which are prepared by metal-organic chemical vapor deposition (MOCVD) and the γ-CuI films which are prepared by spin-coating. The fabricated heterojunction has a large open circuit voltage (V_oc) of 0.69 V, desired for achieving self-powered operation of a photodetector. Irradiated by 254-nm ultraviolet (UV) light, when the bias voltage is -5 V, the dark current (I_dark) of the device is 0.47 pA, the photocurrent (I_photo) is -50.93 nA, and the photo-to-dark current ratio (I_photo/I_dark) reaches about 1.08×10⁵. The device has a stable and fast response speed in different wavelengths, the rise time (τ_r) and decay time (τ_d) are 0.762 s and 1.741 s under 254-nm UV light illumination, respectively. While the τ_r and τ_d are 10.709 s and 7.241 s under 365-nm UV light illumination, respectively. The time-dependent (I-t) response (photocurrent in the order of 10^-10 A) can be clearly distinguished at a small light intensity of 1 μW·cm^-2. The internal physical mechanism affecting the device performances is discussed by the band diagram and charge carrier transfer theory.

Bright 547-dimensional Hilbert-space entangled resource in 28-pair modes biphoton frequency comb from a reconfigurable silicon microring resonator ^Hot!

Qilin Zheng(郑骑林), Jiacheng Liu(刘嘉成), Chao Wu(吴超), Shichuan Xue(薛诗川), Pingyu Zhu(朱枰谕), Yang Wang(王洋), Xinyao Yu(于馨瑶), Miaomiao Yu(余苗苗), Mingtang Deng(邓明堂), Junjie Wu(吴俊杰), and Ping Xu(徐平)

Chin. Phys. B, 2022, 31 (2): 024206. DOI: 10.1088/1674-1056/ac3507

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High-dimensional entanglement provides valuable resources for quantum technologies, including quantum communication, quantum optical coherence tomography, and quantum computing. Obtaining a high brightness and dimensional entanglement source has significant value. Here we utilize a tunable asymmetric Mach-Zehnder interferometer coupled silicon microring resonator with 100 GHz free spectral range to achieve this goal. With the strategy of the tunable coupler, the dynamical and extensive tuning range of quality factors of the microring can be obtained, and then the biphoton pair generation rate can be optimized. By selecting and characterizing 28 pairs from a more than 30-pair modes biphoton frequency comb, we obtain a Schmidt number of at least 23.4 and on-chip pair generation rate of 19.9 MHz/mW² under a low on-chip pump power, which corresponds to 547 dimensions Hilbert space in frequency freedom. These results will prompt the wide applications of quantum frequency comb and boost the further large density and scalable on-chip quantum information processing.

High sensitivity plasmonic temperature sensor based on a side-polished photonic crystal fiber

Zhigang Gao(高治刚), Xili Jing(井西利), Yundong Liu(刘云东), Hailiang Chen(陈海良), and Shuguang Li(李曙光)

Chin. Phys. B, 2022, 31 (2): 024207. DOI: 10.1088/1674-1056/ac0a63

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A high sensitivity plasmonic temperature sensor based on a side-polished photonic crystal fiber is proposed in this work. In order to achieve high sensitivity and high stability, the gold layer is coated on the side-polished photonic crystal fiber to support surface plasmon resonance. The mixture of ethanol and chloroform is used as the thermosensitive liquid. The performances of the proposed temperature sensor were investigated by the finite element method (FEM). Simulation results indicate that the sensitivity of the temperature sensor is as high as 7.82 nm/℃. It has good linearity (R²=0.99803), the resolution of 1.1×10^-3℃, and the amplitude sensitivity of 0.1008℃^-1. In addition, the sizes of the small air hole and polishing depth have little influence on the sensitivity. Therefore, the proposed sensor shows a high structure tolerance. The excellent performance and high structure tolerance of the sensor make it an appropriate choice for temperature measurement.

Digital synthesis of programmable photonic integrated circuits

Juan Zhang(张娟), Zhengyong Ji(计正勇), Yipeng Ding(丁一鹏), and Yang Wang(王阳)

Chin. Phys. B, 2022, 31 (2): 024208. DOI: 10.1088/1674-1056/ac0da9

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Programmable photonic waveguide meshes can be programmed into many different circuit topologies and thereby provide a variety of functions. Due to the complexity of the signal routing in a general mesh, a particular synthesis algorithm often only accounts for a specific function with a specific cell configuration. In this paper, we try to synthesize the programmable waveguide mesh to support multiple configurations with a more general digital signal processing platform. To show the feasibility of this technique, photonic waveguide meshes in different configurations (square, triangular and hexagonal meshes) are designed to realize optical signal interleaving with arbitrary duty cycles. The digital signal processing (DSP) approach offers an effective pathway for the establishment of a general design platform for the software-defined programmable photonic integrated circuits. The use of well-developed DSP techniques and algorithms establishes a link between optical and electrical signals and makes it convenient to realize the computer-aided design of optics-electronics hybrid systems.

Non-Rayleigh photon statistics of superbunching pseudothermal light

Chao-Qi Wei(卫超奇), Jian-Bin Liu(刘建彬), Xue-Xing Zhang(张学星), Rui Zhuang(庄睿), Yu Zhou(周宇), Hui Chen(陈辉), Yu-Chen He(贺雨晨), Huai-Bin Zheng(郑淮斌), and Zhuo Xu(徐卓)

Chin. Phys. B, 2022, 31 (2): 024209. DOI: 10.1088/1674-1056/ac0ba9

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Superbunching pseudothermal light has important applications in studying the second- and higher-order interference of light in quantum optics. Unlike the photon statistics of thermal or pseudothermal light is well understood, the photon statistics of superbunching pseudothermal light has not been studied yet. In this paper, we will employ single-photon detectors to measure the photon statistics of superbunching pseudothermal light and calculate the degree of second-order coherence. It is found that the larger the value of the degree of second-order coherence of superbunching pseudothermal light is, the more the measured photon distribution deviates from the one of thermal or pseudothermal light in the tail part. The results are helpful to understand the physics of two-photon superbunching with classical light. It is suggested that superbunching pseudothermal light can be employed to generate non-Rayleigh temporal speckles.

Refractive index sensing of double Fano resonance excited by nano-cube array coupled with multilayer all-dielectric film

Xiangxian Wang(王向贤), Jian Zhang(张健), Jiankai Zhu(朱剑凯), Zao Yi(易早), and Jianli Yu(余建立)

Chin. Phys. B, 2022, 31 (2): 024210. DOI: 10.1088/1674-1056/ac3816

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We propose a hybrid structure of a nano-cube array coupled with multilayer full-dielectric thin films for refractive index sensing. In this structure, discrete states generated by two-dimensional grating and continuous states generated by a photonic crystal were coupled at a specific wavelength to form two Fano resonances. The transmission spectra and electric field distributions of the structure were obtained via the finite-difference time-domain method. We obtained the optimal structural parameters after optimizing the geometrical parameters. Under the optimal parameters, the figure of merit (FOM) values of the two Fano resonances reached 1.7×10⁴ and 3.9×10³, respectively. These results indicate that the proposed structure can achieve high FOM refractive index sensing, thus offering extensive application prospects in the biological and chemical fields.

A novel polarization converter based on the band-stop frequency selective surface

Kun Liao(廖昆), Shining Sun(孙世宁), Xinyuan Zheng(郑昕原), Xianxian Shao(邵纤纤), Xiangkun Kong(孔祥鲲), and Shaobin Liu(刘少斌)

Chin. Phys. B, 2022, 31 (2): 024211. DOI: 10.1088/1674-1056/ac1fdd

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A dual-passband single-polarized converter based on the band-stop frequency selective surface (FSS) with a low radar cross-section (RCS) is designed in this article. The unit cell of the proposed converter is formed by a polarization layer attached to the band-stop frequency selective surface. The simulation results reveal that the co-polarization reflection coefficients below -10 dB are achieved in 3.82-13.64 GHz with a 112.4% fractional bandwidth (the ratio of the signal bandwidth to the central frequency). Meanwhile, a polarization conversion band is realized from 8.14 GHz to 9.27 GHz with a polarization conversion ratio which is over 80%. Moreover, the 1 dB transmission window is obtained in two non-adjacent bands of 3.42-7.02 GHz and 10.04-13.91 GHz corresponding to the relative bandwidths of 68.9% and 32.3%, respectively. Furthermore, the radar cross-section of the designed structure can be reduced in the wideband from 2.28 GHz to 14 GHz, and the 10 dB RCS reduction in the range of 4.10-13.35 GHz is achieved. In addition, the equivalent circuit model of this converter is established, and the simulation results of the Advanced Design System (ADS) match well with those of CST Microwave Studio (CST). The archetype of the designed converter is manufactured and measured. The experiment results match the simulation results well, which proves the reliability of the simulation results.

Effects of pulse energy ratios on plasma characteristics of dual-pulse fiber-optic laser-induced breakdown spectroscopy

Yu-Hua Hang(杭玉桦), Yan Qiu(邱岩), Ying Zhou(周颖), Tao Liu(刘韬), Bin Zhu(朱斌), Kaixing Liao(廖开星), Ming-Xin Shi(时铭鑫), and Fei Xue(薛飞)

Chin. Phys. B, 2022, 31 (2): 024212. DOI: 10.1088/1674-1056/ac1fdb

Abstract ( 419 )

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Laser-induced plasmas of dual-pulse fiber-optic laser-induced breakdown spectroscopy with different pulse energy ratios are studied by using the optical emission spectroscopy (OES) and fast imaging. The energy of the two laser pulses is independently adjusted within 0-30 mJ with the total energy fixed at 30 mJ. The inter-pulse delay remains 450 ns constantly. As the energy share of the first pulse increases, a similar bimodal variation trend of line intensities is observed. The two peaks are obtained at the point where the first pulse is half or twice of the second one, and the maximum spectral enhancement is at the first peak. The bimodal variation trend is induced by the change in the dominated mechanism of dual-pulse excitation with the trough between the two peaks caused by the weak coupling between the two mechanisms. By increasing the first pulse energy, there is a transition from the ablation enhancement dominance near the first peak to the plasma reheating dominance near the second peak. The calculations of plasma temperature and electron number density are consistent with the bimodal trend, which have the values of 17024.47 K, 2.75×10¹⁷ cm^-3 and 12215.93 K, 1.17×10¹⁷ cm^-3 at a time delay of 550 ns. In addition, the difference between the two peaks decreases with time delay. With the increase in the first pulse energy share, the plasma morphology undergoes a transformation from hemispherical to shiny-dot and to oblate-cylinder structure during the second laser irradiation from the recorded images by using an intensified charge-coupled device (ICCD) camera. Correspondingly, the peak expansion distance of the plasma front first decreases significantly from 1.99 mm in the single-pulse case to 1.34 mm at 12/18 (dominated by ablation enhancement) and then increases slightly with increasing the plasma reheating effect. The variations in plasma dynamics verify that the change of pulse energy ratios leads to a transformation in the dual-pulse excitation mechanism.

Simulation of detection and scattering of sound waves by the lateral line of a fish

V M Adamyan, I Y Popov, I V Blinova, and V V Zavalniuk

Chin. Phys. B, 2022, 31 (2): 024301. DOI: 10.1088/1674-1056/ac1b81

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A solvable model of lateral line of a fish based on a wave equation with additional boundary conditions on a set of isolated points is proposed. Within the framework of this model it is shown that the ratio of pressures on lateral lines on different fish flanks, as well as the cross section of sound scattering on both the lines, strongly depends on angles of incidence of incoming sound waves. The strong angular dependence of the pressure ratio seems to be sufficient for the fish to determine the directions from which the sound is coming.

Deep learning for image reconstruction in thermoacoustic tomography

Qiwen Xu(徐启文), Zhu Zheng(郑铸), and Huabei Jiang(蒋华北)

Chin. Phys. B, 2022, 31 (2): 024302. DOI: 10.1088/1674-1056/ac0dab

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Microwave-induced thermoacoustic tomography (TAT) is a rapidly-developing noninvasive imaging technique that integrates the advantages of microwave imaging and ultrasound imaging. While an image reconstruction algorithm is critical for the TAT, current reconstruction methods often creates significant artifacts and are computationally costly. In this work, we propose a deep learning-based end-to-end image reconstruction method to achieve the direct reconstruction from the sinogram data to the initial pressure density image. We design a new network architecture TAT-Net to transfer the sinogram domain to the image domain with high accuracy. For the scenarios where realistic training data are scarce or unavailable, we use the finite element method (FEM) to generate synthetic data where the domain gap between the synthetic and realistic data is resolved through the signal processing method. The TAT-Net trained with synthetic data is evaluated through both simulations and phantom experiments and achieves competitive performance in artifact removal and robustness. Compared with other state-of-the-art reconstruction methods, the TAT-Net method can reduce the root mean square error to 0.0143, and increase the structure similarity and peak signal-to-noise ratio to 0.988 and 38.64, respectively. The results obtained indicate that the TAT-Net has great potential applications in improving image reconstruction quality and fast quantitative reconstruction.

Nearfield acoustic holography in a moving medium based on particle velocity input using nonsingular propagator

Bi-Chun Dong(董必春), Run-Mei Zhang(张润梅), Bin Yuan(袁彬), and Chuan-Yang Yu(俞传阳)

Chin. Phys. B, 2022, 31 (2): 024303. DOI: 10.1088/1674-1056/ac46c2

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Nearfield acoustic holography in a moving medium is a technique which is typically suitable for sound sources identification in a flow. In the process of sound field reconstruction, sound pressure is usually used as the input, but it may contain considerable background noise due to the interactions between microphones and flow moving at a high velocity. To avoid this problem, particle velocity is an alternative input, which can be obtained by using laser Doppler velocimetry in a non-intrusive way. However, there is a singular problem in the conventional propagator relating the particle velocity to the pressure, and it could lead to significant errors or even false results. In view of this, in this paper, nonsingular propagators are deduced to realize accurate reconstruction in both cases that the hologram is parallel to and perpendicular to the flow direction. The advantages of the proposed method are analyzed, and simulations are conducted to verify the validation. The results show that the method can overcome the singular problem effectively, and the reconstruction errors are at a low level for different flow velocities, frequencies, and signal-to-noise ratios.

Correlation mechanism between force chains and friction mechanism during powder compaction

Ning Zhang(张宁), Shuai Zhang(张帅), Jian-Jun Tan(谈健君), and Wei Zhang(张炜)

Chin. Phys. B, 2022, 31 (2): 024501. DOI: 10.1088/1674-1056/ac0db1

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The relation between friction mechanism and force chains characteristics has not yet been fully studied in the powder metallurgy research area. In this work, a uniaxial compression discrete element model is established based on the compaction process of ferrous powder. Furthermore, the correlation mechanism between force chains and the friction mechanism during powder compaction is investigated. The simulation results reveal a strong correlation between the variation of the friction coefficient and the evolution of force chains. During the powder compaction, the friction coefficient would eventually tend to be stable, a feature which is also closely related to the slip ratio between particles. The side wall friction and the friction between particles would have an important effect on the direction of force chain growth in about one-third of the area near the side wall. The research results provide theoretical guidance for improving the densification process of the powder according to the force chain and friction.

Modeling the heterogeneous traffic flow considering the effect of self-stabilizing and autonomous vehicles

Yuan Gong(公元) and Wen-Xing Zhu(朱文兴)

Chin. Phys. B, 2022, 31 (2): 024502. DOI: 10.1088/1674-1056/ac2b18

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With the increasing maturity of automatic driving technology, the homogeneous traffic flow will gradually evolve into the heterogeneous traffic flow, which consists of human-driving and autonomous vehicles. To better study the characteristics of the heterogeneous traffic system, this paper proposes a new car-following model for autonomous vehicles and heterogeneous traffic flow, which considers the self-stabilizing effect of vehicles. Through linear and nonlinear methods, this paper deduces and analyzes the stability of such a car-following model with the self-stabilizing effect. Finally, the model is verified by numerical simulation. Numerical results show that the self-stabilizing effect can make the heterogeneous traffic flow more stable, and that increasing the self-stabilizing coefficient or historical time length can strengthen the stability of heterogeneous traffic flow and alleviate traffic congestion effectively. In addition, the heterogeneous traffic flow can also be stabilized with a higher proportion of autonomous vehicles.

Lattice Boltzmann model for interface capturing of multiphase flows based on Allen-Cahn equation

He Wang(王贺), Fang-Bao Tian(田方宝), and Xiang-Dong Liu(刘向东)

Chin. Phys. B, 2022, 31 (2): 024701. DOI: 10.1088/1674-1056/ac11d8

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A phase-field-based lattice Boltzmann model is proposed for the interface capturing of multi-phase flows based on the conservative Allen-Cahn equation (ACE). By adopting the improved form of a relaxation matrix and an equilibrium distribution function, the time derivative ∂_t(φu) induced by recovering the diffusion term in ACE is eliminated. The conducted Chapman-Enskog analysis demonstrates that the correct conservative ACE is recovered. Four benchmark cases including Zalesak's disk rotation, vortex droplet, droplet impact on thin film, and Rayleigh-Taylor instability are investigated to validate the proposed model. The numerical results indicate that the proposed model can accurately describe the complex interface deformation.

Experimental investigation on drag reduction in a turbulent boundary layer with a submerged synthetic jet

Biao-Hui Li(李彪辉), Kang-Jun Wang(王康俊), Yu-Fei Wang(王宇飞), and Nan Jiang(姜楠)

Chin. Phys. B, 2022, 31 (2): 024702. DOI: 10.1088/1674-1056/ac0da6

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This work investigates the active control of a fully developed turbulent boundary layer by a submerged synthetic jet actuator. The impacts of the control are explored by measuring the streamwise velocities using particle image velocimetry, and reduction of the skin-friction drag is observed in a certain range downstream of the orifice. The coherent structure is defined and extracted using a spatial two-point correlation function, and it is found that the synthetic jet can efficiently reduce the streamwise scale of the coherent structure. Proper orthogonal decomposition analysis reveals that large-scale turbulent kinetic energy is significantly attenuated with the introduction of a synthetic jet. The conditional averaging results show that the induction effect of the prograde vortex on the low-speed fluid in a large-scale fluctuation velocity field is deadened, thereby suppressing the bursting process near the wall.

Molecular dynamics simulations on the wet/dry self-latching and electric fields triggered wet/dry transitions between nanosheets: A non-volatile memory nanostructure ^Hot!

Jianzhuo Zhu(朱键卓), Xinyu Zhang(张鑫宇), Xingyuan Li(李兴元), and Qiuming Peng(彭秋明)

Chin. Phys. B, 2022, 31 (2): 024703. DOI: 10.1088/1674-1056/ac3811

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We design a nanostructure composing of two nanoscale graphene sheets parallelly immersed in water. Using molecular dynamics simulations, we demonstrate that the wet/dry state between the graphene sheets can be self-latched; moreover, the wet→dry/dry→wet transition takes place when applying an external electric field perpendicular/parallel to the graphene sheets (E_⊥/E_||). This structure works like a flash memory device (a non-volatile memory):the stored information (wet and dry states) of the system can be kept spontaneously, and can also be rewritten by external electric fields. On the one hand, when the distance between the two nanosheets is close to a certain distance, the free energy barriers for the transitions dry→wet and wet→dry can be quite large. As a result, the wet and dry states are self-latched. On the other hand, an E_⊥ and an E_|| will respectively increase and decrease the free energy of the water located in-between the two nanosheets. Consequently, the wet→dry and dry→wet transitions are observed. Our results may be useful for designing novel information memory devices.

Long-time evolution of charged grains in plasma under harmonic external force and after being withdrawn

Miao Guan(管苗), Zhi-Dong Chen(陈志东), Meng-Die Li(李梦蝶), Zhong-Mao Liu(刘忠茂), You-Mei Wang(汪友梅), and Ming-Yang Yu(郁明阳)

Chin. Phys. B, 2022, 31 (2): 025201. DOI: 10.1088/1674-1056/ac0e27

Abstract ( 390 )

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Evolution of the charged grains in a two-dimensional dusty plasma under a spatially harmonic external force, in particular, their long-time behaviors after the force has been withdrawn, is studied by using molecular dynamics simulation. Under an external force and a grain-grain interaction force, initially homogeneously distributed grains can reach a quasi-stationary state in the form of a disk crystal. After the external force is withdrawn, the disk moves initially with its size and shape nearly unchanged until it rapidly stops moving, and eventually the disk grain rotates like a vortex. The time needed to reach the final state increases with the strength of the initial external force increasing.

Electron acceleration during magnetic islands coalescence and division process in a guide field reconnection

Shengxing Han(韩圣星), Huanyu Wang(王焕宇), and Xinliang Gao(高新亮)

Chin. Phys. B, 2022, 31 (2): 025202. DOI: 10.1088/1674-1056/ac21c0

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The magnetic merging process related to pairwise magnetic islands coalescence is investigated by two-dimensional particle-in-cell simulations with a guide field. Owing to the force of attraction between parallel currents within the initial magnetic islands, the magnetic islands begin to approach each other and merge into one big island. We find that this newly formed island is unstable and can be divided into two small magnetic islands spontaneously. Lastly, these two small islands merge again. We follow the time evolution of this process, in which the contributions of three mechanisms of electron acceleration at different stages, including the Fermi, parallel electric field, and betatron mechanisms, are studied with the guide center theory.

Scaling of rise time of drive current on development of magneto-Rayleigh-Taylor instabilities for single-shell Z-pinches

Xiaoguang Wang(王小光), Guanqiong Wang(王冠琼), Shunkai Sun(孙顺凯), Delong Xiao(肖德龙), Ning Ding(丁宁), Chongyang Mao(毛重阳), and Xiaojian Shu(束小建)

Chin. Phys. B, 2022, 31 (2): 025203. DOI: 10.1088/1674-1056/ac1fd9

Abstract ( 409 )

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In fast Z-pinches, rise time of drive current plays an important role in development of magneto-Rayleigh-Taylor (MRT) instabilities. It is essential for applications of Z-pinch dynamic hohlraum (ZPDH), which could be used for driving inertial confinement fusion (ICF), to understand the scaling of rise time on MRTs. Therefore, a theoretical model for nonlinear development of MRTs is developed according to the numerical analysis. It is found from the model that the implosion distance L=r₀-r_mc determines the development of MRTs, where r₀ is the initial radius and r_mc is the position of the accelerating shell. The current rise time τ would affect the MRT development because of its strong coupling with the r₀. The amplitude of MRTs would increase with the rise time linearly if an implosion velocity is specified. The effects of the rise time on MRT, in addition, are studied by numerical simulation. The results are consistent with those of the theoretical model very well. Finally, the scaling of the rise time on amplitude of MRTs is obtained for a specified implosion velocity by the theoretical model and numerical simulations.

Spatial characteristics of nanosecond pulsed micro-discharges in atmospheric pressure He/H₂O mixture by optical emission spectroscopy Suggested by editors

Chuanjie Chen(陈传杰), Zhongqing Fang(方忠庆), Xiaofang Yang(杨晓芳), Yongsheng Fan(樊永胜), Feng Zhou(周锋), and Rugang Wang(王如刚)

Chin. Phys. B, 2022, 31 (2): 025204. DOI: 10.1088/1674-1056/ac2e62

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Atmospheric pressure micro-discharges in helium gas with a mixture of 0.5% water vapor between two pin electrodes are generated with nanosecond overvoltage pulses. The temporal and spatial characteristics of the discharges are investigated by means of time-resolved imaging and optical emission spectroscopy with respect to the discharge morphology, gas temperature, electron density, and excited species. The evolution of micro-discharges is captured by intensified CCD camera and electrical properties. The gas temperature is diagnosed by a two-temperature fit to the ro-vibrational OH(A²Σ⁺-X²Π, 0-0) emission band and is found to remain low at 425 K during the discharge pulses. The profile of electron density performed by the Stark broadening of H_α 656.1-nm and He I 667.8-nm lines is uniform across the discharge gap at the initial of discharge and reaches as high as 10²³ m^-3. The excited species of He, OH, and H show different spatio-temporal behaviors from each other by the measurement of their emission intensities, which are discussed qualitatively in regard of their plasma kinetics.

Analysis of electromagnetic pulses generated from ultrashort laser irradiation of solid targets at CLAPA

Yi-Lin Xu(徐毅麟), Dong-Yu Li(李东彧), Ya-Dong Xia(夏亚东), Si-Yuan Zhang(张思源), Min-Jian Wu(吴旻剑), Tong Yang(杨童), Jun-Gao Zhu(朱军高), Hao Cheng(程浩), Chuan-Ke Wang(王传珂), Chen Lin(林晨), Ting-Shuai Li(李廷帅), and Xue-Qing Yan(颜学庆)

Chin. Phys. B, 2022, 31 (2): 025205. DOI: 10.1088/1674-1056/ac3735

Abstract ( 466 )

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Electromagnetic pulses (EMPs) produced by the interaction of a TW femtosecond laser with solid targets at the Compact Laser Plasma Accelerator (CLAPA) are measured and interpreted. The statistical results confirm that the intensities of the EMPs are closely related to both target material and thickness. The signal of the titanium target is more abundant than that of the copper target with the same thickness, and the intensity of EMP is positively correlated with the target thickness for aluminium foil. With the boosted EMP radiations, the energy of accelerated protons is also simultaneously enhanced. In addition, EMPs emitted from the front of the target exceed those from the rear, which are also pertinent to the specific target position. The resonant waveforms in the target chamber are analyzed using the fast Fourier transform, and the local resonance and the attenuation lead to changes of the frequency spectra of EMPs with variation of detecting positions, which is well supported by the modeling results. The findings are beneficial to gaining insight into the mechanism of EMP propagation in a typical target chamber and providing more information for EMP shielding design.

Effect of structural vacancies on lattice vibration, mechanical, electronic, and thermodynamic properties of Cr₅BSi₃

Tian-Hui Dong(董天慧), Xu-Dong Zhang(张旭东), Lin-Mei Yang(杨林梅), and Feng Wang(王峰)

Chin. Phys. B, 2022, 31 (2): 026101. DOI: 10.1088/1674-1056/ac11e2

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In recent years, transition metal silicides have become the potential high temperature materials. The ternary silicide has attracted the attention of scientists and researchers. But their inherent brittle behaviors hinder their wide applications. In this work, we use the first-principles method to design four vacancy defects and discuss the effects of vacancy defects on the structural stability, mechanical properties, electronic and thermodynamic properties of hexagonal Cr₅BSi₃ silicide. The data of lattice vibration and thermodynamic parameters indicate that the Cr₅BSi₃ with different atomic vacancies can possess the structural stabilities. The different atomic vacancies change the mechanical properties and induce the Cr₅BSi₃ to implement the brittle-to-ductile transition. The shear deformation resistance and volume deformation resistance of Cr₅BSi₃ are weakened by different vacancy defects. But the brittleness behavior is remarkably improved. The structural stability and brittle-to-ductile transition of Cr₅BSi₃ with different vacancies are explored by the electronic structures. Moreover, the thermal parameters indicate that the Cr₅BSi₃ with vacancies exhibit different thermodynamic properties with temperature rising.

First-principles study of two new boron nitride structures: C12-BN and O16-BN

Hao Wang(王皓), Yaru Yin(殷亚茹), Xiong Yang(杨雄), Yanrui Guo(郭艳蕊), Ying Zhang(张颖), Huiyu Yan(严慧羽), Ying Wang(王莹), and Ping Huai(怀平)

Chin. Phys. B, 2022, 31 (2): 026102. DOI: 10.1088/1674-1056/ac0a69

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Based on the first-principles method, we predict two new stable BN allotropes:C12-BN and O16-BN, which belong to cubic and orthorhombic crystal systems, respectively. It is confirmed that both the phases are thermally and dynamically stable. The results of molecular dynamics simulations suggest that both the BN phases are highly stable even at high temperatures of 1000 K. In the case of mechanical properties, C12-BN has a bulk modulus of 359 GPa and a hardness of 43.4 GPa, making it a novel superhard material with potential technological and industrial applications. Electronic band calculations reveal that both C12-BN and O16-BN are insulators with direct band gaps of 3.02 eV and 3.54 eV, respectively. The XRD spectra of C12-BN and O16-BN are also simulated to provide more information for possible experimental observation. Our findings enrich the BN allotrope family and are expected to stimulate further experimental interest.

Cluster dynamics modeling of niobium and titanium carbide precipitates in α-Fe and γ-Fe

Nadezda Korepanova, Long Gu(顾龙), Mihai Dima, and Hushan Xu(徐瑚珊)

Chin. Phys. B, 2022, 31 (2): 026103. DOI: 10.1088/1674-1056/ac0cd0

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Kinetic behaviors of niobium and titanium carbide precipitates in iron are simulated with cluster dynamics. The simulations, carried out in austenite and ferrite for niobium carbides, and in austenite for titanium carbide, are analyzed for dependences on temperature, solute concentration, and initial cluster distribution. The results are presented for different temperatures and solute concentrations, compared to experimental data available. They show little impact of initial cluster distribution beyond a certain relaxation time and that highly dilute alloys with monomers only present a significantly different behavior from denser alloys or ones with different initial cluster distributions.

A new direct band gap silicon allotrope o-Si32

Xin-Chao Yang(杨鑫超), Qun Wei(魏群), Mei-Guang Zhang(张美光), Ming-Wei Hu(胡明玮), Lin-Qian Li(李林茜), and Xuan-Min Zhu(朱轩民)

Chin. Phys. B, 2022, 31 (2): 026104. DOI: 10.1088/1674-1056/ac11db

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Silicon is a preferred material in solar cells, and most of silicon allotropes have an indirect band gap. Therefore, it is important to find new direct band gap silicon. In the present work, a new direct band gap silicon allotrope of o-Si32 is discovered. The elastic constants, elastic anisotropy, phonon spectra, and electronic structure of o-Si32 are obtained using first-principles calculations. The results show that o-Si32 is mechanically and dynamically stable and is a direct semiconductor material with a band gap of 1.261 eV.

Theoretical study of novel B-C-O compoundswith non-diamond isoelectronic Suggested by editors

Chao Liu(刘超) and Pan Ying(应盼)

Chin. Phys. B, 2022, 31 (2): 026201. DOI: 10.1088/1674-1056/ac0cd2

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Two novel non-isoelectronic with diamond (non-IED) B-C-O phases (tI16-B₈C₆O₂ and mP16-B₈C₅O₃) have been unmasked. The research of the phonon scattering spectra and the independent elastic constants under ambient pressure (AP) and high pressure (HP) proves the stability of these non-IED B-C-O phases. Respective to the common compounds, the research of the formation enthalpies and the relationship with pressure of all non-IED B-C-O phases suggests that HP technology performed in the diamond anvil cell (DAC) or large volume press (LVP) is an important technology for synthesis. Both tI16-B₈C₆O₂ and tI12-B₆C₄O₂ possess electrical conductivity. mP16-B₈C₅O₃ is a small bandgap semiconductor with a 0.530 eV gap. For aP13-B₆C₂O₅, mC20-B₂CO₂ and tI18-B₄CO₄ are all large gap semiconductors with gaps of 5.643 eV, 6.113 eV, and 7.105 eV, respectively. The study on the relationship between band gap values and pressure of these six non-IED B-C-O phases states that tI16-B₈C₆O₂ and tI12-B₆C₄O₂ maintain electrical conductivity, mC20-B₂CO₂ and tI18-B₄CO₄ have good bandgap stability and are less affected by pressure. The stress-strain simulation reveals that the max strain and stress of 0.4 GPa and 141.9 GPa respectively, can be sustained by tI16-B₈C₆O₂. Studies on their mechanical properties shows that they all possess elasticity moduli and hard character. And pressure has an obvious effect on their mechanical properties, therein toughness of tI12-B₆C₄O₂, aP13-B₆C₂O₅, mC20-B₂CO₂ and tI18-B₄CO₄ all increases, and hardness of mP16-B₈C₅O₃ continue to strengthen during the compression. With abundant hardness characteristics and tunable band gaps, extensive attention will be focused on the scientific research of non-IED B-C-O compounds.

Collective modes of type-II Weyl fermions with repulsive S-wave interaction ^Hot!

Xun-Gao Wang(王勋高), Yuan Sun(孙远), Liang Liu(刘亮), and Wu-Ming Liu(刘伍明)

Chin. Phys. B, 2022, 31 (2): 026701. DOI: 10.1088/1674-1056/ac3d81

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Three-dimensional type-II Weyl fermions possess overtilted cone-like low-energy band dispersion. Unlike the closed ellipsoidal Fermi surface for type-I Weyl fermions, the Fermi surface is an open hyperboloid for type-II Weyl fermions. We evaluate the spin and density susceptibility of type-II Weyl fermions with repulsive S-wave interaction by means of Green's functions. We obtain the particle-hole continuum along the tilted momentum direction and perpendicular to the tilted momentum direction respectively. We find the zero sound mode in some repulsive interaction strengths by numerically solving the pole equations of the susceptibility within the random-phase approximation.

Invariable mobility edge in a quasiperiodic lattice

Tong Liu(刘通), Shujie Cheng(成书杰), Rui Zhang(张锐), Rongrong Ruan(阮榕榕), and Houxun Jiang(姜厚勋)

Chin. Phys. B, 2022, 31 (2): 027101. DOI: 10.1088/1674-1056/ac140e

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We analytically and numerically study a 1D tight-binding model with tunable incommensurate potentials. We utilize the self-dual relation to obtain the critical energy, namely, the mobility edge. Interestingly, we analytically demonstrate that this critical energy is a constant independent of strength of potentials. Then we numerically verify the analytical results by analyzing the spatial distributions of wave functions, the inverse participation rate and the multifractal theory. All numerical results are in excellent agreement with the analytical results. Finally, we give a brief discussion on the possible experimental observation of the invariable mobility edge in the system of ultracold atoms in optical lattices.

Stability, electronic structure, and optical properties of lead-free perovskite monolayer Cs₃B₂X₉ (B=Sb, Bi; X=Cl, Br, I) and bilayer vertical heterostructure Cs₃B₂X₉/Cs₃B₂'X₉ (B,B'=Sb, Bi; X=Cl, Br, I) Suggested by editors

Yaowen Long(龙耀文), Hong Zhang(张红), and Xinlu Cheng(程新路)

Chin. Phys. B, 2022, 31 (2): 027102. DOI: 10.1088/1674-1056/ac2e5f

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The lead-free perovskites Cs₃B₂X₉ (B=Sb, Bi; X=Cl, Br, I) as the popular photoelectric materials have excellent optical properties with lower toxicity. In this study, we systematically investigate the stable monolayer Cs₃B₂X₉ and bilayer vertical heterostructure Cs₃B₂X₉//Cs₃B₂'X₉ (B, B'=Sb, Bi; X=Cl, Br, I) via first-principles simulations. By exploring the electrical structures and band edge positions, we find the band gap reduction and the band type transition in the heterostructure Cs₃B₂X₉//Cs₃B₂'X₉ due to the charge transfer between layers. Furthermore, the results of optical properties reveal light absorption from the visible light to UV region, especially monolayer Cs₃Sb₂I₉ and heterostructure Cs₃Sb₂I₉/Cs₃Bi₂I₉, which have absorption peaks in the visible light region, leading to the possibility of photocatalytic water splitting. These results provide insights for more two-dimensional semiconductors applied in the optoelectronic and photocatalytic fields.

High linearity AlGaN/GaN HEMT with double-V_th coupling for millimeter-wave applications Suggested by editors

Pengfei Wang(王鹏飞), Minhan Mi(宓珉瀚), Meng Zhang(张濛), Jiejie Zhu(祝杰杰), Yuwei Zhou(周雨威), Jielong Liu(刘捷龙), Sijia Liu(刘思佳), Ling Yang(杨凌), Bin Hou(侯斌), Xiaohua Ma(马晓华), and Yue Hao(郝跃)

Chin. Phys. B, 2022, 31 (2): 027103. DOI: 10.1088/1674-1056/ac2b21

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We demonstrated an AlGaN/GaN high electron mobility transistor (HEMT) namely double-V_th coupling HEMT (DVC-HEMT) fabricated by connecting different threshold voltage (V_th) values including the slant recess element and planar element in parallel along the gate width with N₂O plasma treatment on the gate region. The comparative studies of DVC-HEMT and Fin-like HEMT fabricated on the same wafer show significantly improved linearity of transconductance (G_m) and radio frequency (RF) output signal characteristics in DVC-HEMT. The fabricated device shows the transconductance plateau larger than 7 V, which yields a flattened f_T/f_max-gate bias dependence. At the operating frequency of 30 GHz, the peak power-added efficiency (PAE) of 41% accompanied by the power density (P_out) of 5.3 W/mm. Furthermore, the proposed architecture also features an exceptional linearity performance with 1-dB compression point (P_{1 dB}) of 28 dBm, whereas that of the Fin-like HEMT is 25.2 dBm. The device demonstrated in this article has great potential to be a new paradigm for millimeter-wave application where high linearity is essential.

Thermoelectric transport in conductive poly(3,4-ethylenedioxythiophene)

Meng Li(李萌), Zuzhi Bai(柏祖志), Xiao Chen(陈晓), Cong-Cong Liu(刘聪聪), Jing-Kun Xu(徐景坤), Xiao-Qi Lan(蓝小琪), and Feng-Xing Jiang(蒋丰兴)

Chin. Phys. B, 2022, 31 (2): 027201. DOI: 10.1088/1674-1056/ac4230

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Poly(3,4-ethylenedioxythiophene) (PEDOT) has proved its quite competitive thermoelectric properties in flexible electronics with its excellent electrical and mechanical properties. Since the early discovery of PEDOT, considerable experimental progress has been achieved in optimizing and improving the thermoelectric properties as a promising organic thermoelectric material (OTE). Among them, theoretical research has made significant contributions to its development. Here the basic physics of conductive PEDOT are reviewed based on the combination of theory and experiment. The purpose is to provide a new insight into the development of PEDOT, so as to effectively design and preparation of advanced thermoelectric PEDOT material in the future.

High power-added-efficiency AlGaN/GaN HEMTs fabricated by atomic level controlled etching Suggested by editors

Xinchuang Zhang(张新创), Bin Hou(侯斌), Fuchun Jia(贾富春), Hao Lu(芦浩), Xuerui Niu(牛雪锐), Mei Wu(武玫), Meng Zhang(张濛), Jiale Du(杜佳乐), Ling Yang(杨凌), Xiaohua Ma(马晓华), and Yue Hao(郝跃)

Chin. Phys. B, 2022, 31 (2): 027301. DOI: 10.1088/1674-1056/ac1414

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An atomic-level controlled etching (ACE) technology is invstigated for the fabrication of recessed gate AlGaN/GaN high-electron-mobility transistors (HEMTs) with high power added efficiency. We compare the recessed gate HEMTs with conventional etching (CE) based chlorine, Cl₂-only ACE and BCl₃/Cl₂ ACE, respectively. The mixed radicals of BCl₃/Cl₂ were used as the active reactants in the step of chemical modification. For ensuring precise and controllable etching depth and low etching damage, the kinetic energy of argon ions was accurately controlled. These argon ions were used precisely to remove the chemical modified surface atomic layer. Compared to the HEMTs with CE, the characteristics of devices fabricated by ACE are significantly improved, which benefits from significant reduction of etching damage. For BCl₃/Cl₂ ACE recessed HEMTs, the load pull test at 17 GHz shows a high power added efficiency (PAE) of 59.8% with an output power density of 1.6 W/mm at V_d=10 V, and a peak PAE of 44.8% with an output power density of 3.2 W/mm at V_d=20 V in a continuous-wave mode.

Enhanced thermoelectric performance of PEDOT: PSS films via ionic liquid post-treatment

Jiaji Yang(杨家霁), Xuejing Li(李雪晶), Yanhua Jia(贾艳华), Jiang Zhang(张弜), and Qinglin Jiang(蒋庆林)

Chin. Phys. B, 2022, 31 (2): 027302. DOI: 10.1088/1674-1056/ac2487

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Thermoelectric (TE) energy harvesting can effectively convert waste heat into electricity, which is a crucial technology to solve energy concerns. As a promising candidate for energy conversion, poly(3,4-ethylenedioxythiophene):poly (styrene sulfonate) (PEDOT:PSS) has gained significant attention owing to its easy doping, high transparency, and solution processability. However, the TE performance of PEDOT:PSS still needs to be further enhanced. Herein, different approaches have been applied for tuning the TE properties:(i) direct dipping PEDOT:PSS thin films in ionic liquid; (ii) post-treatment of the films with concentrated sulfuric acid (H₂SO₄), and then dipping in ionic liquid. Besides, the same bis(trifluoromethanesulfonyl)amide (TFSI) anion and different cation salts, including 1-ethyl-3-methylimidazolium (EMIM⁺) and lithium (Li⁺), are selected to study the influence of varying cation types on the TE properties of PEDOT:PSS. The Seebeck coefficient and electrical conductivity of the PEDOT:PSS film treated with H₂SO₄EMIM:TFSI increase simultaneously, and the resulting maximum power factor is 46.7 μW·m^-1·K^-2, which may be attributed to the ionic liquid facilitating the rearrangement of the molecular chain of PEDOT. The work provides a reference for the development of organic films with high TE properties.

Facile fabrication of highly flexible, porous PEDOT: PSS/SWCNTs films for thermoelectric applications

Fu-Wei Liu(刘福伟), Fei Zhong(钟飞), Shi-Chao Wang(王世超), Wen-He Xie(谢文合), Xue Chen(陈雪), Ya-Ge Hu(胡亚歌), Yu-Ying Ge(葛钰莹), Yuan Gao(郜源), Lei Wang(王雷), and Zi-Qi Liang(梁子骐)

Chin. Phys. B, 2022, 31 (2): 027303. DOI: 10.1088/1674-1056/ac3502

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High-performance organic composite thermoelectric (TE) materials are considered as a promising alternative for harvesting heat energy. Herein, composite films of poly (3,4-ethyienedioxythiophene):poly(styrene sulfonate)/single-walled carbon nanotubes (PEDOT:PSS/SWCNTs) were fabricated by utilizing a convenient solution mixing method. Thereafter, the as-prepared hybrid films were treated using sulfuric acid (H₂SO₄) to further optimize the TE performance. Film morphological studies revealed that the sulfuric acid treated PEDOT:PSS/SWCNTs composite samples all possessed porous structures. Due to the successful fabrication of highly conductive networks, the porous nano-architecture also exhibited much more excellent TE properties when compared with the dense structure of the pristine samples. For the post-treated sample, a high power factor of 156.43 μW· m^-1· K^-2 can be achieved by adjusting the content of CNTs, which is approximately 3 orders of magnitude higher than that of the corresponding untreated samples (0.23 μW· m^-1· K^-2). Besides, the obtained films also showed excellent mechanical flexibility, owing to the porous nanostructure and the strong π-π interactions between the two components. This work indicates that the H₂SO₄ treatment could be a promising strategy for fabricating highly-flexible and porous PEDOT:PSS/SWCNTs films with high TE performances.

Quantum transport signatures of non-trivial topological edge states in a ring-shaped Su-Schrieffer-Heeger double-chain system

Cheng-Zhi Ye(叶成芝), Lan-Yun Zhang(张蓝云), and Hai-Bin Xue(薛海斌)

Chin. Phys. B, 2022, 31 (2): 027304. DOI: 10.1088/1674-1056/ac34ff

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In the ring-shaped Su-Schrieffer-Heeger (SSH) double-chain, the quantum interference between the two different electron tunneling paths of the upper and lower chains has an important influence on the electron transport properties of non-trivial topological edge states. Here, we have studied the electron transport signatures of non-trivial topological edge states in a ring-shaped SSH double-chain system based on the wave-guide theory and transfer-matrix method. In the ring-shaped SSH double-chain with the upper chain being different from the lower one, it is demonstrated that the electron transmission probability displays the four and two resonance peaks associated with the non-trivial topological edge states in the weak and strong coupling regimes, respectively. Whereas in the case of the upper chain being the same as the lower one, the two transmission resonance peaks associated with the non-trivial topological edge states in the weak coupling regime are only found, and that in the strong coupling regime disappear that originated from the destructive interference between the two different electron tunneling paths of the upper and lower chains. Consequently, the variation of the number of transmission resonance peaks associated with the non-trivial topological edge states in the weak and strong coupling regimes suggests that an alternative scheme for detecting non-trivial topological edge states in the ring-shaped SSH double-chain system.

Raman phonon anomalies in Sr(Fe_1-xCo_x)₂As₂

Yanxing Yang(杨彦兴), Hewei Zhang(张鹤巍), and Haizheng Zhuang(庄海正)

Chin. Phys. B, 2022, 31 (2): 027401. DOI: 10.1088/1674-1056/ac0cd6

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Phonon anomalies have been reported in iron-pnictide superconductors indicating a diverse interplay between different orders in the materials. Here, we report Raman scattering measurements on Sr(Fe_1-xCo_x)₂As₂ (x=0 and x=0.04) single crystals in the B_2g symmetry with respect to a 1 Fe unit cell. Upon cooling, we observe a larger split (13 cm^-1) of E_g Raman phonon modes pertaining to in-plane Fe and As displacements as the crystals undergo the tetragonal-to-orthorhombic structural phase transition, although a considerable split (9 cm^-1) has been reported in Ba(Fe_1-xCo_x)₂As₂. Furthermore, the splitting of E_g phonon modes is strongly reduced upon doping. We perform an order-parameter analysis revealing a similar doping dependence of E_g phonon splitting as reported in other compounds of the 122 family, indicating these phonon anomalies widely exist in 122 iron-based superconductors and might share the same mechanisms.

Tailoring the optical and magnetic properties of La-BaM hexaferrites by Ni substitution

Hafiz T. Ali, M. Ramzan, M Imran Arshad, Nicola A. Morley, M. Hassan Abbas, Mohammad Yusuf, Atta Ur Rehman, Khalid Mahmood, Adnan Ali, Nasir Amin, and M. Ajaz-un-Nabi

Chin. Phys. B, 2022, 31 (2): 027502. DOI: 10.1088/1674-1056/ac1412

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We investigate the impact of Ni insertion on the structural, optical, and magnetic properties of Ba_0.8La_0.2Fe_12-xNi_xO₁₉ hexaferrites (Ni substituted La-BaM hexaferrites). Samples were prepared using the conventional co-precipitation method and sintered at 1000℃ for 4 hours to assist the crystallization process. An analysis of the structure of the samples was carried out using an x-ray diffraction (XRD) spectrometer. The M-type hexagonal structure of all the samples was confirmed using XRD spectra. The lattice parameters a and c were found to be in the ranges of 5.8925 ±0.001 nm-5.8952 ±0.001 nm and 23.2123 ±0.001 nm-23.2219 ±0.001 nm, respectively. The M-type hexagonal nature of the prepared samples was also indicated by the presence of corresponding FT-IR bands and Raman modes in the FT-IR and Raman spectra, respectively. EDX results confirmed the successful synthesis of the samples according to the required stoichiometric ratio. A UV-vis spectrometer was used to record the absorption spectra of the prepared samples in the wavelength range of 200 nm-1100 nm. The optical energy bandgap of the samples was found to be in the range of 1.21 eV-3.39 eV. The M-H loops of the samples were measured at room temperature at an applied magnetic field range of 0 kOe-60 kOe. A high saturation magnetization of 99.92 emu/g was recorded in the sample with x=0 at a microwave operating frequency of 22.2 GHz. This high value of saturation magnetization is due to the substitution of La³⁺ ions at the spin-up (12k, 2a, and 2b) sites. The Ni substitution is proven to be a potential candidate for the tuning of the optical and magnetic parameters of M-type hexaferrites. Therefore, we suggest that the prepared samples are suitable for use in magneto-optic applications.

Hysteresis loss reduction in self-bias FeSi/SrFe₁₂O₁₉ soft magnetic composites Suggested by editors

Shuangjiu Feng(冯双久), Jiangli Ni(倪江利), Feng Hu(胡锋), Xucai Kan(阚绪材), Qingrong Lv(吕庆荣), and Xiansong Liu(刘先松)

Chin. Phys. B, 2022, 31 (2): 027503. DOI: 10.1088/1674-1056/ac2d1a

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The magnetic field provided by magnetized SrFe₁₂O₁₉ particles in FeSi/SrFe₁₂O₁₉ composites is used to replace the applied transverse magnetic field, which successfully reduces the magnetic loss of the composites with minor reduction of permeability. This magnetic loss reduction mainly comes from the decrease in hysteresis loss, while the eddy current loss is basically unaffected. The hysteresis loss reduction in magnetized composites is believed to be due to the decrease in domain wall displacement caused by the increase in the average magnetic domain size in a DC magnetic field. This is an effective method for reducing the magnetic loss of soft magnetic composites with wide application potential, and there is no problem of increasing the cost and the volume of the magnetic cores.

Spin current transmission in Co_1-xTb_x films Suggested by editors

Li Wang(王力), Yangtao Su(苏仰涛), Yang Meng(孟洋), Haibin Shi(石海滨), Xinyu Cao(曹昕宇), and Hongwu Zhao(赵宏武)

Chin. Phys. B, 2022, 31 (2): 027504. DOI: 10.1088/1674-1056/ac3d83

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We investigate the spin to charge conversion phenomena in Y₃Fe₅O₁₂/Pt/Co_1-xTb_x/Pt multilayers by both the spin pumping and spin Seebeck effects. We find that the spin transport efficiency is irrelevant to magnetization states of the perpendicular magnetized Co_1-xTb_x films, which can be attributed to the symmetry requirement of the inverse transverse spin Hall effect. Furthermore, the spin transmission efficiency is significantly affected by the film concentration, revealing the dominant role of extrinsic impurity scattering caused by Tb impurity. The present results provide further guidance for enhancing the spin transport efficiency and developing spintronic devices.

Gilbert damping in the layered antiferromagnet CrCl₃

Xinlin Mi(米锌林), Ledong Wang(王乐栋), Qi Zhang(张琪), Yitong Sun(孙艺彤), Yufeng Tian(田玉峰), Shishen Yan(颜世申), and Lihui Bai(柏利慧)

Chin. Phys. B, 2022, 31 (2): 027505. DOI: 10.1088/1674-1056/ac11cc

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We theoretically and experimentally studied the Gilbert damping evolution of both acoustic and optical magnetic resonance modes in the layered flake CrCl₃ with an external magnetic field H applied in plane. Based on a Lagrangian equation and a Rayleigh dissipation function, we predicted that the resonance linewidth ΔH as a function of microwave frequency ω is nonlinear for both acoustic and optical modes in the CrCl₃ flake, which is significantly different from the linear relationship of ΔH ∝ ω in ferromagnets. Measuring the microwave transmission through the CrCl₃ flake, we obtained the ω-H dispersion and damping evolution ΔH-ω for both acoustic and optical modes. Combining both our theoretical prediction and experimental observations, we concluded that the nonlinear damping evolution ΔH-ω is a consequence of the interlayer interaction during the antiferromagnetic resonance, and the interlayer Gilbert dissipation plays an important role in the nonlinear damping evolution because of the asymmetry of the non-collinear magnetizaiton between layers.

Perpendicular magnetization and exchange bias in epitaxial NiO/[Ni/Pt]₂ multilayers Suggested by editors

Lin-Ao Huang(黄林傲), Mei-Yu Wang(王梅雨), Peng Wang(王鹏), Yuan Yuan(袁源), Ruo-Bai Liu(刘若柏), Tian-Yu Liu(刘天宇), Yu Lu(卢羽), Jia-Rui Chen(陈家瑞), Lu-Jun Wei(魏陆军), Wei Zhang(张维), Biao You(游彪), Qing-Yu Xu(徐庆宇), and Jun Du(杜军)

Chin. Phys. B, 2022, 31 (2): 027506. DOI: 10.1088/1674-1056/ac2b22

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The realization of perpendicular magnetization and perpendicular exchange bias (PEB) in magnetic multilayers is important for the spintronic applications. NiO(t)/[Ni(4 nm)/Pt(1 nm)]₂ multilayers with varying the NiO layer thickness t have been epitaxially deposited on SrTiO₃ (001) substrates. Perpendicular magnetization can be achieved when t < 25 nm. Perpendicular magnetization originates from strong perpendicular magnetic anisotropy (PMA), mainly resulting from interfacial strain induced by the lattice mismatch between the Ni and Pt layers. The PMA energy constant decreases monotonically with increasing t, due to the weakening of Ni (001) orientation and a little degradation of the Ni-Pt interface. Furthermore, significant PEB can be observed though NiO layer has spin compensated (001) crystalline plane. The PEB field increases monotonically with increasing t, which is considered to result from the thickness dependent anisotropy of the NiO layer.

Radiation resistance property of barium gallo-germanate glass doped by Nb₂O₅

Gui-Rong Liu(刘桂榕), Xiao-Dong Chen(陈晓东), Hong-Gang Liu(刘红刚), Yan Wang(王琰), Min Sun(孙敏), Na Yan(闫娜), Qi Qian(钱奇), and Zhong-Min Yang(杨中民)

Chin. Phys. B, 2022, 31 (2): 027801. DOI: 10.1088/1674-1056/ac2b1a

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Effects of Nb₂O₅ dopant on the radiation response of barium gallo-germanate (BGG) glass are studied mainly by electron paramagnetic resonance and absorption spectroscopy. Owing to the Nb⁵⁺↔Nb³⁺ interconversion in doped samples, formations of Ge-related non-bridging oxygen hole center and Ge-related electron center defects after γ-ray irradiation are inhibited. Thereby, Nb₂O₅ dopant can enhance radiation resistance of BGG glass, and 1.0% Nb₂O₅ concentration is the best.

Majorana fermions induced fast- and slow-light in a hybrid semiconducting nanowire/superconductor device Suggested by editors

Hua-Jun Chen(陈华俊), Peng-Jie Zhu(朱鹏杰), Yong-Lei Chen(陈咏雷), and Bao-Cheng Hou(侯宝成)

Chin. Phys. B, 2022, 31 (2): 027802. DOI: 10.1088/1674-1056/ac3221

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We investigate theoretically Rabi-like splitting and Fano resonance in absorption spectra of quantum dots (QDs) based on a hybrid QD-semiconducting nanowire/superconductor (SNW/SC) device mediated by Majorana fermions (MFs). Under the condition of pump on-resonance and off-resonance, the absorption spectrum experiences the conversion from Fano resonance to Rabi-like splitting in different parametric regimes. In addition, the Fano resonances are accompanied by the rapid normal phase dispersion, which will indicate the coherent optical propagation. The results indicate that the group velocity index is tunable with controlling the interaction between the QD and MFs, which can reach the conversion between the fast- and slow-light. Fano resonance will be another method to detect MFs and our research may indicate prospective applications in quantum information processing based on the hybrid QD-SNW/SC devices.

Ultrafast proton transfer dynamics of 2-(2'-hydroxyphenyl)benzoxazole dye in different solvents

Simei Sun(孙四梅), Song Zhang(张嵩), Jiao Song(宋娇), Xiaoshan Guo(郭小珊), Chao Jiang(江超), Jingyu Sun(孙静俞), and Saiyu Wang(王赛玉)

Chin. Phys. B, 2022, 31 (2): 027803. DOI: 10.1088/1674-1056/ac3734

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The excited-state intramolecular proton transfer of 2-(2'-hydroxyphenyl)benzoxazole dye in different solvents is investigated using ultrafast femtosecond transient absorption spectroscopy combined with quantum chemical calculations. Conformational conversion from the syn-enol configuration to the keto configuration is proposed as the mechanism of excited-state intramolecular proton transfer. The duration of excited-state intramolecular proton transfer is measured to range from 50 fs to 200 fs in different solvents. This time is strongly dependent on the calculated energy gap between the N-S₀ and T-S₁ structures in the S₁ state. Along the proton transfer reaction coordinate, the vibrational relaxation process on the S₁ state potential surface is observed. The duration of the vibrational relaxation process is determined to be from 8.7 ps to 35 ps dependent on the excess vibrational energy.

Secondary electron emission yield from vertical graphene nanosheets by helicon plasma deposition

Xue-Lian Jin(金雪莲), Pei-Yu Ji(季佩宇), Lan-Jian Zhuge(诸葛兰剑), Xue-Mei Wu(吴雪梅), and Cheng-Gang Jin(金成刚)

Chin. Phys. B, 2022, 31 (2): 027901. DOI: 10.1088/1674-1056/ac11dd

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The secondary electron emission yields of materials depend on the geometries of their surface structures. In this paper, a method of depositing vertical graphene nanosheet (VGN) on the surface of the material is proposed, and the secondary electron emission (SEE) characteristics for the VGN structure are studied. The COMSOL simulation and the scanning electron microscope (SEM) image analysis are carried out to study the secondary electron yield (SEY). The effect of aspect ratio and packing density of VGN on SEY under normal incident condition are studied. The results show that the VGN structure has a good effect on suppressing SEE.

Determination of the surface states from the ultrafast electronic states in a thermoelectric material ^Hot!

Tongyao Wu(吴桐尧), Hongyuan Wang(王洪远), Yuanyuan Yang(杨媛媛), Shaofeng Duan(段绍峰), Chaozhi Huang(黄超之), Tianwei Tang(唐天威), Yanfeng Guo(郭艳峰), Weidong Luo(罗卫东), and Wentao Zhang(张文涛)

Chin. Phys. B, 2022, 31 (2): 027902. DOI: 10.1088/1674-1056/ac373c

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We reveal the electronic structure in YbCd₂Sb₂, a thermoelectric material, by angle-resolved photoemission spectroscopy (ARPES) and time-resolved ARPES (trARPES). Specifically, three bulk bands at the vicinity of the Fermi level are evidenced near the Brillouin zone center, consistent with the density functional theory (DFT) calculation. It is interesting that the spin-unpolarized bulk bands respond unexpectedly to right- and left-handed circularly polarized probe. In addition, a hole band of surface states, which is not sensitive to the polarization of the probe beam and is not expected from the DFT calculation, is identified. We find that the non-equilibrium quasiparticle recovery rate is much smaller in the surface states than that of the bulk states. Our results demonstrate that the surface states can be distinguished from the bulk ones from a view of time scale in the nonequilibrium physics.

Recent advances in organic, inorganic, and hybrid thermoelectric aerogels

Lirong Liang(梁丽荣), Xiaodong Wang(王晓东), Zhuoxin Liu(刘卓鑫), Guoxing Sun(孙国星), and Guangming Chen(陈光明)

Chin. Phys. B, 2022, 31 (2): 027903. DOI: 10.1088/1674-1056/ac2802

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The thermoelectric (TE) materials and corresponding TE devices can achieve direct heat-to-electricity conversion, thus have wide applications in heat energy harvesting (power generator), wearable electronics and local cooling. In recent years, aerogel-based TE materials have received considerable attention and have made remarkable progress because of their unique structural, electrical and thermal properties. In this review, the recent progress in both organic, inorganic, and composite/hybrid TE aerogels is systematically summarized, including the main constituents, preparation method, TE performance, as well as factors affecting the TE performance and the corresponding mechanism. Moreover, two typical aerogel-based TE devices/generators are compared and analyzed in terms of assembly modes and output performance. Finally, the present challenges and some tentative suggestions for future research prospects are provided in conclusion.

SnO₂/Co₃O₄ nanofibers using double jets electrospinning as low operating temperature gas sensor

Zhao Wang(王昭), Shu-Xing Fan(范树兴), and Wei Tang(唐伟)

Chin. Phys. B, 2022, 31 (2): 028101. DOI: 10.1088/1674-1056/ac1336

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SnO₂/Co₃O₄ nanofibers (NFs) are synthesized by using a homopolar electrospinning system with double jets of positive polarity electric fields. The morphology and structure of SnO₂/Co₃O₄ hetero-nanofibers are characterized by using field emission scanning electron microscope (FE-SEM), transmission electron microscope (TEM), x-ray diffraction (XRD), and x-ray photoelectron spectrometer (XPS). The analyses of SnO₂/Co₃O₄ NFs by EDS and HRTEM show that the cobalt and tin exist on one nanofiber, which is related to the homopolar electrospinning and the crystallization during sintering. As a typical n-type semiconductor, SnO₂ has the disadvantages of high optimal operating temperature and poor reproducibility. Comparing with SnO₂, the optimal operating temperature of SnO₂/Co₃O₄ NFs is reduced from 350℃ to 250℃, which may be related to the catalysis of Co₃O₄. The response of SnO₂/Co₃O₄ to 100-ppm ethanol at 250℃ is 50.9, 9 times higher than that of pure SnO₂, which may be attributed to the p-n heterojunction between the n-type SnO₂ crystalline grain and the p-type Co₃O₄ crystalline grain. The nanoscale p-n heterojunction promotes the electron migration and forms an interface barrier. The synergy effects between SnO₂ and Co₃O₄, the crystalline grain p-n heterojunction, the existence of nanofibers and the large specific surface area all jointly contribute to the improved gas sensing performance.

Numerical study of growth competition between twin grains during directional solidification by using multi-phase field method

Chang-Sheng Zhu(朱昶胜), Ting Wang(汪婷), Li Feng(冯力), Peng Lei(雷鹏), and Fang-Lan Ma(马芳兰)

Chin. Phys. B, 2022, 31 (2): 028102. DOI: 10.1088/1674-1056/ac0eed

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A multi-phase field model is established to simulate the growth competition and evolution behavior between seaweed and columnar dendrites during directional solidification. According to the effects of surface tension and interfacial energy, we quantitatively analyze the influences of factors such as inclination angles, pulling velocity, and anisotropic strength on twin growth. The results demonstrate that the pulling velocity and anisotropic strength have an important influence on the morphology and evolution of the seaweed and dendritic growth. The low pulling velocity and anisotropic strength are both key parameters for maintaining the stable morphology of seaweed during competitive growth in a bicrystal, showing that the lateral branching behavior is the root of the dendrites that can ultimately dominate the growth. And it is clarified that the lateral branching behavior and lateral blocking are the root causes of the final dominant growth of dendrites. With the increase of anisotropy strength, the seaweed is eliminated fastest in case 1, the seaweed is transformed into degenerate dendritic morphology, and eliminates the seaweed by promoting the generation and lateral growth of the lateral branches of the dendrites. The increase of pulling velocity is to increase the undercooling of favorable oriented grain and accelerate the growth rate of dendrites, thus producing more new primary dendrites for lateral expansion and accelerating the elimination rate of unfavorable oriented grain.

Thermoelectric characteristics of flexible reduced graphene oxide/silver selenide nanowire composites prepared by a facile vacuum filtration process

Zuo Xiao(肖佐), Yong Du(杜永), Qiufeng Meng(孟秋风), and Lei Wang(王磊)

Chin. Phys. B, 2022, 31 (2): 028103. DOI: 10.1088/1674-1056/ac447e

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The reduced graphene oxide/silver selenide nanowire (rGO/Ag₂Se NW) composite powders were fabricated via a wet chemical approach, and then flexible rGO/Ag₂Se NW composite film was prepared by a facile vacuum filtration method combined with cold-pressing treatment. A highest power factor of 228.88 μW·m^-1·K^-2 was obtained at 331 K for the cold-pressed rGO/Ag₂Se NW composite film with 0.01 wt% rGO. The rGO/Ag₂Se NW composite film revealed superior flexibility as the power factor retained 94.62% after bending for 500 times with a bending radius of 4 mm, which might be due to the interwoven network structures of Ag₂Se NWs and pliability of rGO as well as nylon membrane. These results demonstrated that the GO/Ag₂Se NW composite film has a potential for preparation of flexible thermoelectric devices.

Enhancing the thermoelectric performance through the mutual interaction between conjugated polyelectrolytes and single-walled carbon nanotubes

Shuxun Wan(万树勋), Zhongming Chen(陈忠明), Liping Hao(郝丽苹), Shichao Wang(王世超), Benzhang Li(李本章), Xiao Li(黎潇), Chengjun Pan(潘成军), and Lei Wang(王雷)

Chin. Phys. B, 2022, 31 (2): 028104. DOI: 10.1088/1674-1056/ac48f9

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We present a method of constructing composites composed of conjugated polyelectrolytes (CPEs) and single-walled carbon nanotubes (SWCNTs) to obtain a high-performing flexible thermoelectric generator. In this approach, three kinds of polymers, namely, poly[(1,4-(2,5-didodecyloxybenzene)-alt-2,5-thiophene] (P1), poly[(1,4-(2,5-bis-sodium butoxysulfonate-phenylene)-alt-2,5-thiophene] (P2), and poly[(1,4-(2,5-bis-acid butoxysulfonic-phenylene)-alt-2,5-thiophene] (P3) are designed, synthesized and complexed with SWCNTs as thermoelectric composites. The electrical conductivities of the CPEs/SWCNTs (P2/SWCNTs, and P3/SWCNTs) nanocomposites are much higher than those of non-CPEs/SWCNTs (P1/SWCNTs) nanocomposites. Among them, the electrical conductivity of P2/SWCNTs with a ratio of 1:4 reaches 3686 S·cm^-1, which is 12.4 times that of P1/SWCNTs at the same SWCNT mass ratio. Moreover, CPEs/SWCNTs composites (P2/SWCNTs) display remarkably improved thermoelectric properties with the highest power factor (PF) of 163 μW·m^-1·K^-2. In addition, a thermoelectric generator is fabricated with P2/SWCNTs composite films, and the output power and power density of this generator reach 1.37 μW and 1.4 W·m^-2 (cross-section) at ΔT=70 K. This result is over three times that of the thermoelectric generator composed of non-CPEs/SWCNTs composite films (P1/SWCNTs, 0.37 μW). The remarkably improved electrical conductivities and thermoelectric properties of the CPEs/SWCNTs composites (P2/SWCNTs) are attributed to the enhanced interaction. This method for constructing CPEs/SWCNTs composites can be applied to produce thermoelectric materials and devices.

Palladium nanoparticles/wool keratin-assisted carbon composite-modified flexible and disposable electrochemical solid-state pH sensor Suggested by editors

Wenli Zhang(张文立), Xiaotian Liu(刘笑天), Youhui Lin(林友辉), Liyun Ma(马利芸), Linqing Kong(孔令庆), Guangzong Min(闵光宗), Ronghui Wu(吴荣辉), Sharwari K. Mengane, Likun Yang(杨丽坤), Aniruddha B. Patil, and Xiang Yang Liu(刘向阳)

Chin. Phys. B, 2022, 31 (2): 028201. DOI: 10.1088/1674-1056/ac3ca9

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Several pH-dependent processes and reactions take place in the human body; hence, the pH of body fluids is the best indicator of disturbed health conditions. However, accurate and real-time diagnosis of the pH of body fluids is complicated because of limited commercially available pH sensors. Hence, we aimed to prepare a flexible, transparent, disposable, user-friendly, and economic strip-based solid-state pH sensor using palladium nanoparticles (PdNPs)/N-doped carbon (NC) composite material. The PdNPs/NC composite material was synthesized using wool keratin (WK) as a precursor. The in-situ prepared PdNPs played a key role in the controlled switching of protein structure to the N-doped carbon skeleton with π-π arrangement at the mesoscale level, which mimics the A-B type polymeric structure, and hence, is highly susceptible to H⁺ ions. The optimized carbonization condition in the presence of PdNPs showed that the material obtained using a modified Ag/AgCl reference electrode had the highest pH sensitivity with excellent stability and durability. The optimized pH sensor showed high specificity and selectivity with a sensitivity of 55 mV/pH unit and a relative standard deviation of 0.79%. This study is the first to synthesize PdNPs using WK as a stabilizing and reducing agent. The applicability of the sensor was investigated for biological samples, namely, saliva and gastric juices. The proposed protocol and material have implications in solid-state chemistry, where biological material will be the best choice for the synthesis of materials with anticipated performance.

Ultrafast dynamics of cationic electronic states of vinyl bromide by strong-field ionization-photofragmentation Suggested by editors

Long-Xing Zhou(周龙兴), Yang Liu(刘洋), Shen He(贺屾), Da-Shuai Gao(高大帅), Xing-Chen Shen(沈星晨), Qi Chen(陈淇), Tao Yu(于涛), Hang Lv(吕航), and Hai-Feng Xu(徐海峰)

Chin. Phys. B, 2022, 31 (2): 028202. DOI: 10.1088/1674-1056/ac2b15

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Strong field ionization-photofragmentation (SFI-PF) with ultrafast pump-probe scheme is a powerful approach to study the dynamics of molecular cationic electronic states. Here we carry out a SFI-PF study on the cationic electronic states of vinyl bromide, C₂H₃Br. The yields of the parent C₂H₃Br⁺ and the formation of the fragment (Br⁺, C₂H₂⁺ and C₂H₃⁺) ions have been measured at different pump-probe delay time. Analysis provides experimental evidence of A²A'-X²A" internal conversion of vinyl bromide cations which occurs in a time of about 220 fs, and the time of C₂H₃⁺ formation induced by the dissociation of the A²A' state around 300 fs. The study would add our knowledge of the behavior of electronic excited states of complex molecular cations.

Recent progress in design of conductive polymers to improve the thermoelectric performance

Zhen Xu (徐真), Hui Li (李慧), and Lidong Chen(陈立东)

Chin. Phys. B, 2022, 31 (2): 028203. DOI: 10.1088/1674-1056/ac22a4

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Organic semiconductors, especially polymer semiconductors, have attracted extensive attention as organic thermoelectric materials due to their capabilities for flexibility, low-cost fabrication, solution processability and low thermal conductivity. However, it is challenging to obtain high-performance organic thermoelectric materials because of the low intrinsic carrier concentration of organic semiconductors. The main method to control the carrier concentration of polymers is the chemical doping process by charge transfer between polymer and dopant. Therefore, the deep understanding of doping mechanisms from the point view of chemical structure has been highly desired to overcome the bottlenecks in polymeric thermoelectrics. In this contribution, we will briefly review the recently emerging progress for discovering the structure-property relationship of organic thermoelectric materials with high performance. Highlights include some achievements about doping strategies to effectively modulate the carrier concentration, the design rules of building blocks and side chains to enhance charge transport and improve the doping efficiency. Finally, we will give our viewpoints on the challenges and opportunities in the field of polymer thermoelectric materials.

N-type core-shell heterostructured Bi₂S₃@Bi nanorods/polyaniline hybrids for stretchable thermoelectric generator

Lu Yang(杨璐), Chenghao Liu(刘程浩), Yalong Wang(王亚龙), Pengcheng Zhu(朱鹏程), Yao Wang(王瑶), and Yuan Deng(邓元)

Chin. Phys. B, 2022, 31 (2): 028204. DOI: 10.1088/1674-1056/ac272e

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With the growing need on distributed power supply for portable electronics, energy harvesting from environment becomes a promising solution. Organic thermoelectric (TE) materials have advantages in intrinsic flexibility and low thermal conductivity, thus hold great prospect in applications as a flexible power generator from dissipated heat. Nevertheless, the weak electrical transport behaviors of organic TE materials have severely impeded their development. Moreover, compared with p-type organic TE materials, stable and high-performance n-type counterparts are more difficult to obtain. Here, we developed a n-type polyaniline-based hybrid with core-shell heterostructured Bi₂S₃@Bi nanorods as fillers, showing a Seebeck coefficient -159.4 μV/K at room temperature. Further, a couple of n/p legs from the PANI-based hybrids were integrated into an elastomer substrate forming a stretchable thermoelectric generator (TEG), whose function to output stable voltages responding to temperature differences has been demonstrated. The in situ output performance of the TEG under stretching could withstand up to 75% elongation, and stability test showed little degradation over a one-month period in the air. This study provides a promising strategy to develop stable and high thermopower organic TEGs harvesting heat from environment as long-term power supply.

Modeling of high permittivity insulator structure with interface charge by charge compensation

Zhi-Gang Wang(汪志刚), Yun-Feng Gong(龚云峰), and Zhuang Liu(刘壮)

Chin. Phys. B, 2022, 31 (2): 028501. DOI: 10.1088/1674-1056/ac0cd3

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An analytical model of the power metal-oxide-semiconductor field-effect transistor (MOSFET) with high permittivity insulator structure (HKMOS) with interface charge is established based on superposition and developed for optimization by charge compensation. In light of charge compensation, the disturbance aroused by interface charge is efficiently compromised by introducing extra charge for maximizing breakdown voltage (BV) and minimizing specific ON-resistance (R_on,sp). From this optimization method, it is very efficient to obtain the design parameters to overcome the difficulty in implementing the R_on,sp-BV trade-off for quick design. The analytical results prove that in the HKMOS with positive or negative interface charge at a given length of drift region, the extraction of the parameters is qualitatively and quantitatively optimized for trading off BV and R_on,sp with JFET effect taken into account.

Radiation effects of 50-MeV protons on PNP bipolar junction transistors

Yuan-Ting Huang(黄垣婷), Xiu-Hai Cui(崔秀海), Jian-Qun Yang(杨剑群), Tao Ying(应涛), Xue-Qiang Yu(余雪强), Lei Dong(董磊), Wei-Qi Li(李伟奇), and Xing-Ji Li(李兴冀)

Chin. Phys. B, 2022, 31 (2): 028502. DOI: 10.1088/1674-1056/ac1331

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The effects of radiation on 3CG110 PNP bipolar junction transistors (BJTs) are characterized using 50-MeV protons, 40-MeV Si ions, and 1-MeV electrons. In this paper, electrical characteristics and deep level transient spectroscopy (DLTS) are utilized to analyze radiation defects induced by ionization and displacement damage. The experimental results show a degradation of the current gain and an increase in the types of radiation defect with increasing fluences of 50-MeV protons. Moreover, by comparing the types of damage caused by different radiation sources, the characteristics of the radiation defects induced by irradiation show that 50-MeV proton irradiation can produce both ionization and displacement defects in the 3CG110 PNP BJTs, in contrast to 40-MeV Si ions, which mainly generate displacement defects, and 1-MeV electrons, which mainly produce ionization defects. This work provides direct evidence of a synergistic effect between the ionization and displacement defects caused in PNP BJTs by 50-MeV protons.

A 4H-SiC merged P-I-N Schottky with floating back-to-back diode

Wei-Zhong Chen(陈伟中), Hai-Feng Qin(秦海峰), Feng Xu(许峰), Li-Xiang Wang(王礼祥), Yi Huang(黄义), and Zheng-Sheng Han(韩郑生)

Chin. Phys. B, 2022, 31 (2): 028503. DOI: 10.1088/1674-1056/ac0e23

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A novel 4H-SiC merged P-I-N Schottky (MPS) with floating back-to-back diode (FBD), named FBD-MPS, is proposed and investigated by the Sentaurus technology computer-aided design (TCAD) and analytical model. The FBD features a trench oxide and floating P-shield, which is inserted between the P+/N-(PN) junction and Schottky junction to eliminate the shorted anode effect. The FBD is formed by the N-drift/P-shield/N-drift and it separates the PN and Schottky active region independently. The FBD reduces not only the V_turn to suppress the snapback effect but also the V_on at bipolar operation. The results show that the snapback can be completely eliminated, and the maximum electric field (E_max) is shifted from the Schottky junction to the FBD in the breakdown state.

Development of series SQUID array with on-chip filter for TES detector ^Hot!

Wentao Wu(伍文涛), Zhirong Lin(林志荣), Zhi Ni(倪志), Peizhan Li(李佩展), Tiantian Liang(梁恬恬), Guofeng Zhang(张国峰), Yongliang Wang(王永良), Liliang Ying(应利良), Wei Peng(彭炜), Wen Zhang(张文), Shengcai Shi(史生才), Lixing You(尤立星), and Zhen Wang(王镇)

Chin. Phys. B, 2022, 31 (2): 028504. DOI: 10.1088/1674-1056/ac2b91

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A cold preamplifier based on superconducting quantum interference devices (SQUIDs) is currently the preferred readout technology for the low-noise transition edge sensor (TES). In this work, we have designed and fabricated a series SQUID array (SSA) amplifier for the TES detector readout circuit. In this SSA amplifier, each SQUID cell is composed of a first-order gradiometer formed using two equally large square washers, and an on-chip low pass filter (LPF) as a radio-frequency (RF) choke has been developed to reduce the Josephson oscillation interference between individual SQUID cells. In addition, a highly symmetric layout has been designed carefully to provide a fully consistent embedded electromagnetic environment and achieve coherent flux operation. The measured results show smooth V-Φ characteristics and a swing voltage that increases linearly with increasing SQUID cell number N. A white flux noise level as low as 0.28 μΦ₀/Hz^1/2 is achieved at 0.1 K, corresponding to a low current noise level of 7 pA/Hz^1/2. We analyze the measured noise contribution at mK-scale temperatures and find that the dominant noise derives from a combination of the SSA intrinsic noise and the equivalent current noise of the room temperature electronics.

Impact of STI indium implantation on reliability of gate oxide

Xiao-Liang Chen(陈晓亮), Tian Chen(陈天), Wei-Feng Sun(孙伟锋), Zhong-Jian Qian(钱忠健), Yu-Dai Li(李玉岱), and Xing-Cheng Jin(金兴成)

Chin. Phys. B, 2022, 31 (2): 028505. DOI: 10.1088/1674-1056/ac0e26

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The impacts of shallow trench isolation (STI) indium implantation on gate oxide and device characteristics are studied in this work. The stress modulation effect is confirmed in this research work. An enhanced gate oxide oxidation rate is observed due to the enhanced tensile stress, and the thickness gap is around 5%. Wafers with and without STI indium implantation are manufactured using the 150-nm silicon on insulator (SOI) process. The ramped voltage stress and time to breakdown capability of the gate oxide are researched. No early failure is observed for both wafers the first time the voltage is ramped up. However, a time dependent dielectric breakdown (TDDB) test shows more obvious evidence that the gate oxide quality is weakened by the STI indium implantation. Meanwhile, the device characteristics are compared, and the difference between two devices is consistent with the equivalent oxide thickness (EOT) gap.

Structure design for high performance n-type polymer thermoelectric materials

Qi Zhang(张奇), Hengda Sun(孙恒达), and Meifang Zhu(朱美芳)

Chin. Phys. B, 2022, 31 (2): 028506. DOI: 10.1088/1674-1056/ac3a64

Abstract ( 466 )

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Organic thermoelectric (OTE) materials have been regarded as a potential candidate to harvest waste heat from complex, low temperature surfaces of objects and convert it into electricity. Recently, n-type conjugated polymers as organic thermoelectric materials have aroused intensive research in order to improve their performance to match up with their p-type counterpart. In this review, we discuss aspects that affect the performance of n-type OTEs, and further focus on the effect of planarity of backbone on the doping efficiency and eventually the TE performance. We then summarize strategies such as implementing rigid n-type polymer backbone or modifying conventional polymer building blocks for more planar conformation. In the outlook part, we conclude forementioned devotions and point out new possibility that may promote the future development of this field.

Donor-acceptor conjugated copolymer with high thermoelectric performance: A case study of the oxidation process within chemical doping

Liangjun Chen(陈凉君), Wei Wang(王维), Shengqiang Xiao(肖生强), and Xinfeng Tang(唐新峰)

Chin. Phys. B, 2022, 31 (2): 028507. DOI: 10.1088/1674-1056/ac3504

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The doping process and thermoelectric properties of donor-acceptor (D-A) type copolymers are investigated with the representative poly([2,6'-4,8-di(5-ethylhexylthienyl)benzo[1,2-b;3,3-b] dithiophene]3-fluoro-2-[(2-ethylhexyl)-carbonyl]thieno[3,4-b]thiophenediyl)) (PTB7-Th). The PTB7-Th is doped by FeCl₃ and only polarons are induced in its doped films. The results reveal that the electron-rich donor units within PTB7-Th lose electrons preferentially at the initial stage of the oxidation and then the acceptor units begin to be oxidized at a high doping concentration. The energy levels of polarons and the Fermi level of the doped PTB7-Th remain almost unchange with different doping levels. However, the morphology of the PTB7-Th films could be deteriorated as the doping levels are improved, which is one of the main reasons for the decrease of electrical conductivity at the later stage of doping. The best electrical conductivity and power factor are obtained to be 42.3 S·cm^-1 and 33.9 μW·mK^-2, respectively, in the doped PTB7-Th film at room temperature. The power factor is further improved to 38.3 μW·mK^-2 at 75℃. This work may provide meaningful experience for development of D-A type thermoelectric copolymers and may further improve the doping efficiency.

Terahertz generation and detection of LT-GaAs thin film photoconductive antennas excited by lasers of different wavelengths

Xin Liu(刘欣), Qing-Hao Meng(孟庆昊), Jing Ding(丁晶), Zhi-Chen Bai(白志晨), Jia-Hui Wang(王佳慧), Cong Zhang(张聪), Bo Su(苏波), and Cun-Lin Zhang(张存林)

Chin. Phys. B, 2022, 31 (2): 028701. DOI: 10.1088/1674-1056/ac0cd5

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A new method of generating and detecting terahertz waves is proposed. Low-temperature-grown gallium arsenide (LT-GaAs) thin films are prepared by etching a sacrificial layer (AlAs) in a four-layer epitaxial structure constituted with LT-GaAs, AlAs, GaAs, and semi-insulating gallium arsenide (SI-GaAs). The thin films are then transferred to clean silicon for fabricating the LT-GaAs thin film antennas. The quality and transmission characteristics of the films are analyzed by an 800-nm asynchronous ultrafast time domain spectroscopy system, and the degree of bonding between the film and silicon wafer is determined. Two LT-GaAs thin film antennas for generating and detecting the terahertz waves are tested with a 1550-nm femtosecond laser. The terahertz signal is successfully detected, proving the feasibility of this home-made LT-GaAs photoconductive antennas. This work lays a foundation for studying the mechanism of terahertz wave generation in GaAs photoconductive antennas below the semiconductor band gap.

Iterative filtered ghost imaging

Shao-Ying Meng(孟少英), Mei-Yi Chen(陈美伊), Jie Ji(季杰), Wei-Wei Shi(史伟伟), Qiang Fu(付强), Qian-Qian Bao(鲍倩倩), Xi-Hao Chen(陈希浩), and Ling-An Wu(吴令安)

Chin. Phys. B, 2022, 31 (2): 028702. DOI: 10.1088/1674-1056/ac29a9

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It is generally believed that, in ghost imaging, there has to be a compromise between resolution and visibility. Here we propose and demonstrate an iterative filtered ghost imaging scheme whereby a super-resolution image of a grayscale object is achieved, while at the same time the signal-to-noise ratio (SNR) and visibility are greatly improved, without adding complexity. The dependence of the SNR, visibility, and resolution on the number of iterations is also investigated and discussed. Moreover, with the use of compressed sensing the sampling number can be reduced to less than 1% of the Nyquist limit, while maintaining image quality with a resolution that can exceed the Rayleigh diffraction bound by more than a factor of 10.

Biophysical model for high-throughput tumor and epithelial cell co-culture in complex biochemical microenvironments ^Hot!

Guoqiang Li(李国强), Yanping Liu(刘艳平), Jingru Yao(姚静如), Kena Song(宋克纳), Gao Wang(王高), Lianjie Zhou(周连杰), Guo Chen(陈果), and Liyu Liu(刘雳宇)

Chin. Phys. B, 2022, 31 (2): 028703. DOI: 10.1088/1674-1056/ac381c

Abstract ( 499 )

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The in vivo tumor microenvironment is a complex niche that includes heterogeneous physical structures, unique biochemical gradients and multiple cell interactions. Its high-fidelity in vitro reconstruction is of fundamental importance to improve current understandings of cell behavior, efficacy predictions and drug safety. In this study, we have developed a high-throughput biochip with hundreds of composite extracellular matrix (ECM) microchambers to co-culture invasive breast cancer cells (MDA-MB-231-RFP) and normal breast epithelial cells (MCF-10A-GFP). The composite ECM is composed of type I collagen and Matrigel which provides a heterogeneous microenvironment that is similar to that of in vivo cell growth. Additionally, the growth factors and drug gradients that involve human epidermal growth factor (EGF), discoidin domain receptor 1 (DDR1) inhibitor 7rh and matrix metalloproteinase inhibitor batimastat allow for the mimicking of the complex in vivo biochemical microenvironment to investigate their effect on the spatial-temporal dynamics of cell growth. Our results demonstrate that the MDA-MB-231-RFP cells and MCF-10A-GFP cells exhibit different spatial proliferation behaviors under the combination of growth factors and drugs. Basing on the experimental data, we have also developed a cellular automata (CA) model that incorporated drug diffusion to describe the experimental phenomenon, as well as employed Shannon entropy (SE) to explore the effect of the drug diffusion coefficient on the spatial-temporal dynamics of cell growth. The results indicate that the uniform cell growth is related to the drug diffusion coefficient, which reveals that the pore size of the ECM plays a key role in the formation of complex biochemical gradients. Therefore, our integrated, biomimetic and high-throughput co-culture platforms, as well as the computational model can be used as an effective tool for investigating cancer pathogenesis and drug development.

Collective behavior of cortico-thalamic circuits: Logic gates as the thalamus and a dynamical neuronal network as the cortex

Alireza Bahramian, Sajjad Shaukat Jamal, Fatemeh Parastesh, Kartikeyan Rajagopal, and Sajad Jafari

Chin. Phys. B, 2022, 31 (2): 028901. DOI: 10.1088/1674-1056/ac0eeb

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This paper introduces a two-layer network to investigate the effects of cortico-thalamic circuits on the cortex's collective behavior. In the brain, different parts of the cortex collaborate to process information. One of the main parts, which is the path of different cortex contacts, is the thalamus whose circuit is referred to as the "vertical" cortico-thalamic connectivity. Thalamus subnuclei can participate in the processing of the information that passes through them. It has been shown that they play the functional role of logic gates (AND, OR and XOR). To study how these thalamus circuits affect the cortical neuron behavior, a two-layer network is proposed wherein the cortex layer is composed of Hindmarsh-Rose models and the thalamus layer is constructed with logic gates. Results show that considering these logic gates can lead the network towards different synchronization, asynchronization, chimera and solitary patterns. It is revealed that for AND-gate and OR-gate, increasing the number of gates or their outputs can increase and decrease the network's coherency in excitatory and inhibitory cases, respectively. However, considering XOR-gates always results in the chimera state.

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