Chin. Phys. B

Residual symmetries, consistent-Riccati-expansion integrability, and interaction solutions of a new (3+1)-dimensional generalized Kadomtsev—Petviashvili equation

Jian-Wen Wu(吴剑文), Yue-Jin Cai(蔡跃进), and Ji Lin(林机)

Chin. Phys. B, 2022, 31 (3): 030201. DOI: 10.1088/1674-1056/ac1f08

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With the aid of the Painlevé analysis, we obtain residual symmetries for a new (3+1)-dimensional generalized Kadomtsev—Petviashvili (gKP) equation. The residual symmetry is localized and the finite transformation is proposed by introducing suitable auxiliary variables. In addition, the interaction solutions of the (3+1)-dimensional gKP equation are constructed via the consistent Riccati expansion method. Particularly, some analytical soliton-cnoidal interaction solutions are discussed in graphical way.

Dynamics and near-optimal control in a stochastic rumor propagation model incorporating media coverage and Lévy noise

Liang'an Huo(霍良安) and Yafang Dong(董雅芳)

Chin. Phys. B, 2022, 31 (3): 030202. DOI: 10.1088/1674-1056/ac2f35

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The appearance of rumors intensifies people's panic and affects social stability. How to control the spread of rumors has become an important issue which is worth studying. In order to more accurately reflect the actual situation in the real world, a stochastic model incorporating media coverage and Lévy noise is proposed to describe the dynamic process of rumor propagation. By introducing two control strategies of popular science education and media coverage in an emergency event, an near-optimal control problem that minimizes the influence and control cost of rumor propagation is proposed. Sufficient conditions for near-optimal control of the model are established by using a Hamiltonian function. Then the necessary conditions for near-optimal control are obtained by using the Pontryagin maximum principle. Finally, the effect of popular science education, media coverage and Lévy noise on rumor propagation process control is verified by numerical simulation.

Geometric quantities of lower doubly excited bound states of helium Suggested by editors

Chengdong Zhou(周成栋), Yuewu Yu(余岳武), Sanjiang Yang(杨三江), and Haoxue Qiao(乔豪学)

Chin. Phys. B, 2022, 31 (3): 030301. DOI: 10.1088/1674-1056/ac1b88

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Expectation values of single electron and interelectronic geometric quantities such as $\langle r\rangle$, $\langle r_{12}\rangle$, $\langle r_<\rangle$, $\langle r_>\rangle$, $\langle \cos\theta_{12}\rangle$ and $\langle \theta_{12}\rangle$ are calculated for doubly excited $2{\rm p}n{\rm p}\,{}^1P^{\,\rm e}\,(3\leq n\leq5),\, 2{\rm p}n{\rm p}\,{}^3\!P^{\,\rm e}\,(2\leq n\leq5)$ and $2{\rm p}n{\rm d}\,{}^{1,3}D^{\,\rm o}\,(3\leq n\leq5)$ states of helium using Hylleraas-$B$-spline basis set. The energy levels converge to at least 10 significant digits in our calculations. The extrapolated values of geometric quantities except for $\langle \theta_{12}\rangle$ reach 10 significant digits as well; $\langle \theta_{12}\rangle$ reaches at least 7 significant digits using a multipole expansion approach. Our results provide a precise reference for future research.

Probabilistic resumable quantum teleportation in high dimensions

Xiang Chen(陈想), Jin-Hua Zhang(张晋华), and Fu-Lin Zhang(张福林)

Chin. Phys. B, 2022, 31 (3): 030302. DOI: 10.1088/1674-1056/ac1efb

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Teleportation is a quantum information process without classical counterparts, in which the sender can disembodiedly transfer unknown quantum states to the receiver. In probabilistic teleportation through a partial entangled quantum channel, the transmission is exact (with fidelity 1), but may fail in a probability and the initial state is destroyed simultaneously. We propose a scheme for nondestructive probabilistic teleportation of high-dimensional quantum states. With the aid of an ancilla in the hands of the sender, the initial quantum information can be recovered when teleportation fails. The ancilla acts as a quantum apparatus to measure the sender's subsystem. Erasing the information recorded in it can resume the initial state.

Tetrapartite entanglement measures of generalized GHZ state in the noninertial frames

Qian Dong(董茜), R. Santana Carrillo, Guo-Hua Sun(孙国华), and Shi-Hai Dong(董世海)

Chin. Phys. B, 2022, 31 (3): 030303. DOI: 10.1088/1674-1056/ac2299

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Using a single-mode approximation, we carry out the entanglement measures, e.g., the negativity and von Neumann entropy when a tetrapartite generalized GHZ state is treated in a noninertial frame, but only uniform acceleration is considered for simplicity. In terms of explicit negativity calculated, we notice that the difference between the algebraic average $\pi_{4}$ and geometric average $\varPi_{4}$ is very small with the increasing accelerated observers and they are totally equal when all four qubits are accelerated simultaneously. The entanglement properties are discussed from one accelerated observer to all four accelerated observers. It is shown that the entanglement still exists even if the acceleration parameter $r$ goes to infinity. It is interesting to discover that all 1-1 tangles are equal to zero, but 1-3 and 2-2 tangles always decrease when the acceleration parameter $r$ increases. We also study the von Neumann entropy and find that it increases with the number of the accelerated observers. In addition, we find that the von Neumann entropy $S_{\text{ABCDI}}$, $S_{\text{ABCIDI}}$, $S_{\text{ABICIDI}}$ and $S_{\text{AIBICIDI}}$ always decrease with the controllable angle $\theta$, while the entropies $S_{3-3~\rm non}$, $S_{3-2~\rm non}$, $S_{3-1~\rm non}$ and $S_{3-0~\rm non}$ first increase with the angle $\theta$ and then decrease with it.

Quantum partial least squares regression algorithm for multiple correlation problem

Yan-Yan Hou(侯艳艳), Jian Li(李剑), Xiu-Bo Chen(陈秀波), and Yuan Tian(田源)

Chin. Phys. B, 2022, 31 (3): 030304. DOI: 10.1088/1674-1056/ac1b84

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Partial least squares (PLS) regression is an important linear regression method that efficiently addresses the multiple correlation problem by combining principal component analysis and multiple regression. In this paper, we present a quantum partial least squares (QPLS) regression algorithm. To solve the high time complexity of the PLS regression, we design a quantum eigenvector search method to speed up principal components and regression parameters construction. Meanwhile, we give a density matrix product method to avoid multiple access to quantum random access memory (QRAM) during building residual matrices. The time and space complexities of the QPLS regression are logarithmic in the independent variable dimension n, the dependent variable dimension w, and the number of variables m. This algorithm achieves exponential speed-ups over the PLS regression on n, m, and w. In addition, the QPLS regression inspires us to explore more potential quantum machine learning applications in future works.

Optical scheme to demonstrate state-independent quantum contextuality

Ya-Ping He(何亚平), Deng-Ke Qu(曲登科), Lei Xiao(肖磊), Kun-Kun Wang(王坤坤), and Xiang Zhan(詹翔)

Chin. Phys. B, 2022, 31 (3): 030305. DOI: 10.1088/1674-1056/ac229f

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The contradiction between classical and quantum physics can be identified through quantum contextuality, which does not need composite systems or spacelike separation. Contextuality is proven either by a logical contradiction between the noncontextuality hidden variable predictions and those of quantum mechanics or by the violation of noncontextual inequality. We propose an experimental scheme of state-independent contextual inequality derived from the Mermin proof of the Kochen-Specker (KS) theorem in eight-dimensional Hilbert space, which could be observed either in an individual system or in a composite system. We also show how to resolve the compatibility problems. Our scheme can be implemented in optical systems with current experiment techniques.

Alternative non-Gaussianity measures for quantum states based on quantum fidelity

Cheng Xiang(向成), Shan-Shan Li(李珊珊), Sha-Sha Wen(文莎莎), and Shao-Hua Xiang(向少华)

Chin. Phys. B, 2022, 31 (3): 030306. DOI: 10.1088/1674-1056/ac1928

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We propose three alternative measures for non-Gaussianity of quantum states: sine distance, Bures angle, and Bures distance, which are based on quantum fidelity introduced by Wang [Phys. Lett. A 373 58 (2008)]. Using them, we evaluate the non-Gaussianity of some relevant single-mode and two-mode non-Gaussian states and find a good consistency of the three examined measures. In addition, we show that such metrics can exactly quantify the degree of Gaussianity of even Schrödinger-cat-like states of small amplitudes that can not be measured by other known non-Gaussianity measures such as the Hilbert—Schmidt metric and the relative entropy metric. We make a comparative study between all existing non-Gaussianity measures according to the metric axioms and point out that the sine distance is the best candidate among them.

Measuring Loschmidt echo via Floquet engineering in superconducting circuits ^Hot!

Shou-Kuan Zhao(赵寿宽), Zi-Yong Ge(葛自勇), Zhong-Cheng Xiang(相忠诚), Guang-Ming Xue(薛光明), Hai-Sheng Yan(严海生), Zi-Ting Wang(王子婷), Zhan Wang(王战), Hui-Kai Xu(徐晖凯), Fei-Fan Su(宿非凡), Zhao-Hua Yang(杨钊华), He Zhang(张贺), Yu-Ran Zhang(张煜然), Xue-Yi Guo(郭学仪), Kai Xu(许凯), Ye Tian(田野), Hai-Feng Yu(于海峰), Dong-Ning Zheng(郑东宁), Heng Fan(范桁), and Shi-Ping Zhao(赵士平)

Chin. Phys. B, 2022, 31 (3): 030307. DOI: 10.1088/1674-1056/ac40f8

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The Loschmidt echo is a useful diagnostic for the perfection of quantum time-reversal process and the sensitivity of quantum evolution to small perturbations. The main challenge for measuring the Loschmidt echo is the time reversal of a quantum evolution. In this work, we demonstrate the measurement of the Loschmidt echo in a superconducting 10-qubit system using Floquet engineering and discuss the imperfection of an initial Bell-state recovery arising from the next-nearest-neighbor (NNN) coupling present in the qubit device. Our results show that the Loschmidt echo is very sensitive to small perturbations during quantum-state evolution, in contrast to the quantities like qubit population that is often considered in the time-reversal experiment. These properties may be employed for the investigation of multiqubit system concerning many-body decoherence and entanglement, etc., especially when devices with reduced or vanishing NNN coupling are used.

Quantum properties near the instability boundary in optomechanical system Suggested by editors

Han-Hao Fang(方晗昊), Zhi-Jiao Deng(邓志姣), Zhigang Zhu(朱志刚), and Yan-Li Zhou(周艳丽)

Chin. Phys. B, 2022, 31 (3): 030308. DOI: 10.1088/1674-1056/ac40f7

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The properties of the system near the instability boundary are very sensitive to external disturbances, which is important for amplifying some physical effects or improving the sensing accuracy. In this paper, the quantum properties near the instability boundary in a simple optomechanical system have been studied by numerical simulation. Calculations show that the transitional region connecting the Gaussian states and the ring states when crossing the boundary is sometimes different from the region centered on the boundary line, but it is more essential. The change of the mechanical Wigner function in the transitional region directly reflects its bifurcation behavior in classical dynamics. Besides, quantum properties, such as mechanical second-order coherence function and optomechanical entanglement, can be used to judge the corresponding bifurcation types and estimate the parameter width and position of the transitional region. The non-Gaussian transitional states exhibit strong entanglement robustness, and the transitional region as a boundary ribbon can be expected to replace the original classical instability boundary line in future applications.

Multifractal analysis of the software evolution in software networks

Meili Liu(刘美丽), Xiaogang Qi(齐小刚), and Hao Pan(潘浩)

Chin. Phys. B, 2022, 31 (3): 030501. DOI: 10.1088/1674-1056/ac1b8a

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As the scale and complexity have been increased in software systems, developers place more emphases on software engineering and system designs. Software architecture is evolved with update of softwares, and it plays a fundamental role in determining quality of software systems. Multifractal characteristics of software networks can reflect software quality. In this paper, we construct a software network from the dependencies between object classes, and gain a deep understanding of software through network analysis. To be specific, multifractal analysis of the software network is performed based on a modified box-covering algorithm that yields fewer boxes. We verify that software with different functions and dependencies is multifractal. Further, different versions of the software are compared to discover the evolution of the software architecture. The results show that the singularity of class dependencies decreases as the software is updated. This trend leads to a more specific division of functions between software modules. One of the visible advantages of our work is that it allows the characterization of software structures at the code level. The methodology and results of this paper provide new insights into the evaluation and design of large-scale software systems.

Inferring interactions of time-delayed dynamic networks by random state variable resetting

Changbao Deng(邓长宝), Weinuo Jiang(蒋未诺), and Shihong Wang(王世红)

Chin. Phys. B, 2022, 31 (3): 030502. DOI: 10.1088/1674-1056/ac1e12

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Time delays exist widely in real systems, and time-delayed interactions can result in abundant dynamic behaviors and functions in dynamic networks. Inferring the time delays and interactions is challenging due to systematic nonlinearity, noises, a lack of information, and so on. Recently, Shi et al. proposed a random state variable resetting method to detect the interactions in a continuous-time dynamic network. By arbitrarily resetting the state variable of a driving node, the equivalent coupling functions of the driving node to any response node in the network can be reconstructed. In this paper, we introduce this method in time-delayed dynamic networks. To infer actual time delays, the nearest neighbor correlation (NNC) function for a given time delay is defined. The significant increments of NNC originate from the delayed effect. Based on the increments, the time delays can be reconstructed and the reconstruction errors depend on the sampling time interval. After time delays are accurately identified, the equivalent coupling functions can also be reconstructed. The numerical results have fully verified the validity of the theoretical analysis.

A class of two-dimensional rational maps with self-excited and hidden attractors

Li-Ping Zhang(张丽萍), Yang Liu(刘洋), Zhou-Chao Wei(魏周超),Hai-Bo Jiang(姜海波), and Qin-Sheng Bi(毕勤胜)

Chin. Phys. B, 2022, 31 (3): 030503. DOI: 10.1088/1674-1056/ac4025

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This paper studies a new class of two-dimensional rational maps exhibiting self-excited and hidden attractors. The mathematical model of these maps is firstly formulated by introducing a rational term. The analysis of existence and stability of the fixed points in these maps suggests that there are four types of fixed points, i.e., no fixed point, one single fixed point, two fixed points and a line of fixed points. To investigate the complex dynamics of these rational maps with different types of fixed points, numerical analysis tools, such as time histories, phase portraits, basins of attraction, Lyapunov exponent spectrum, Lyapunov (Kaplan—Yorke) dimension and bifurcation diagrams, are employed. Our extensive numerical simulations identify both self-excited and hidden attractors, which were rarely reported in the literature. Therefore, the multi-stability of these maps, especially the hidden one, is further explored in the present work.

Three-step self-calibrating generalized phase-shifting interferometry

Yu Zhang(张宇)

Chin. Phys. B, 2022, 31 (3): 030601. DOI: 10.1088/1674-1056/ac21c5

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An accurate and fast three-step self-calibrating generalized phase-shifting interferomertry (SGPSI) is proposed. In this approach, two new phase-shifting signals are constructed by the difference interferograms normalization and noise suppressing, then the unknown phase shift between the two difference phase-shifting signals is estimated quickly through searching the minimum coefficient of variation of the modulation amplitude, a limited number of pixels are selected to participate in the search process to further save time, and finally the phase is reconstructed through the searched phase shift. Through the reconstruction of phase map by the simulation and experiment, and the comparison with several mature algorithms, the good performance of the proposed algorithm is proved, and it eliminates the limitation of requiring more than three phase-shifting interferograms for high-precision SGPSI. We expect this method to be widely used in the future.

Finite element simulation of Love wave sensor for the detection of volatile organic gases

Yan Wang(王艳), Su-Peng Liang(梁苏鹏), Shu-Lin Shang(商树林),Yong-Bing Xiao(肖勇兵), and Yu-Xin Yuan(袁宇鑫)

Chin. Phys. B, 2022, 31 (3): 030701. DOI: 10.1088/1674-1056/ac3ec9

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The three-dimensional (3D) finite element (FE) simulation and analysis of Love wave sensors based on polyisobutylene (PIB) layers/SiO$_{2}$/ST-90$^\circ$X quartz structure are presented in this paper, as well as the investigation of coupled resonance effect on the acoustic properties of the devices. The mass sensitivity of the basic Love wave device with SiO$_{2}$ guiding layers is solved analytically. And the highest mass sensitivity of 128 m$^{2}$/kg is obtained as $h_{\rm s}/\lambda =0.175$. The sensitivity of the Love wave sensors for sensing volatile organic compounds (VOCs) is greatly improved due to the presence of coupled resonance induced by the PIB nanorods on the device surface. The frequency shifts of the sensor corresponding to CH$_{2}$Cl$_{2}$, CHCl$_{3}$, CCl$_{4}$, C$_{2}$Cl$_{4}$, CH$_{3}$Cl and C$_{2}$HCl$_{3}$ with the concentration of 100 ppm are 1.431 kHz, 5.507 kHz, 13.437 kHz, 85.948 kHz, 0.127 kHz and 17.879 kHz, respectively. The viscoelasticity influence of the sensitive material on the characteristics of SAW sensors is also studied. By taking account of the viscoelasticity of the PIB layers, the sensitivities of the SAW sensors with the PIB film and PIB nanorods decay in different degree. The gas sensing property of the Love wave sensor with PIB nanorods is superior to that of the PIB films. Meanwhile, the Love wave sensors with PIB sensitive layers show good selectivity to C$_{2}$Cl$_{4}$, making it an ideal selection for gas sensing applications.

Review on typical applications and computational optimizations based on semiclassical methods in strong-field physics

Xun-Qin Huo(火勋琴), Wei-Feng Yang(杨玮枫), Wen-Hui Dong(董文卉), Fa-Cheng Jin(金发成), Xi-Wang Liu(刘希望), Hong-Dan Zhang(张宏丹), and Xiao-Hong Song(宋晓红)

Chin. Phys. B, 2022, 31 (3): 033101. DOI: 10.1088/1674-1056/ac306b

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The semiclassical method based on Feynman's path-integral is in favor of uncovering the quantum tunneling effect, the classical trajectory description of the electron, and the quantum phase information, which can present an intuitive and transparent physical image of electron's propagation in comparison with the ab initio time-dependent Schrödinger equation. In this review, we introduce the basic theoretical concepts and development of several semiclassical methods as well as some of their applications in strong-field physics. Special emphasis is placed on extracting time delay on attosecond scale by the combination of the semiclassical method with phase of phase method. Hundreds of millions of trajectories are generally adopted to obtain a relatively high-resolution photoelectron spectrum, which would take a large amount of time. Here we also introduce several optimization approaches of the semiclassical method to overcome the time-consuming problem of violence calculation.

Strong-field response time and its implications on attosecond measurement

Chao Chen(陈超), Jiayin Che(车佳殷), Xuejiao Xie(谢雪娇), Shang Wang(王赏), Guoguo Xin(辛国国), and Yanjun Chen(陈彦军)

Chin. Phys. B, 2022, 31 (3): 033201. DOI: 10.1088/1674-1056/ac29ab

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To measure and control the electron motion in atoms and molecules by the strong laser field on the attosecond time scale is one of the research frontiers of atomic and molecular photophysics. It involves many new phenomena and processes and raises a series of questions of concepts, theories, and methods. Recent studies show that the Coulomb potential can cause the ionization time lag (about 100 attoseconds) between instants of the field maximum and the ionization-rate maximum. This lag can be understood as the response time of the electronic wave function to the strong-field-induced ionization event. It has a profound influence on the subsequent ultrafast dynamics of the ionized electron and can significantly change the time—frequency properties of electron trajectory (an important theoretical tool for attosecond measurement). Here, the research progress of response time and its implications on attosecond measurement are briefly introduced.

Multi-frequency focusing of microjets generated by polygonal prisms

Yu-Jing Yang(杨育静), De-Long Zhang(张德龙), and Ping-Rang Hua(华平壤)

Chin. Phys. B, 2022, 31 (3): 034201. DOI: 10.1088/1674-1056/ac1930

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We systematically investigate the power distribution characteristics of microjets generated by prismatic scatterers with different shapes at sub-THz region (λ = 8.57 mm). Among these prismatic scatterers, the hexagonal-type one shows better focusing feature than the others. Aiming at the hexagonal-type one, we propose a double-layer scatterer composed of a Teflon hexagonal prism as an outer layer and a semiconductor cuboid as an inner layer. Aiming at the double-layer scatterer, we further study the effects of refractive index, size, and shape of the inner cuboid on microjet's features. The study allows us to present an optimized double-layer scatterer, which has a side length λ /2 (λ) and a refractive index 2.0 (1.4) for the inner (outer) layer. We show that the optimized scatterer can produce an ultra-strong, ultra-narrow microjet with a power enhancement of ~30 and a full width at half maximum (FWHM) of ~0.26λ, and the microjet is just located at the output face. The microjet keeps compact within the distance range of λ from the output face. These features and effects are explained from the viewpoint of ray optics theory. According to the optimized double-layer scatterer, we further study the multi-frequency focusing features of the microjets, and find that the microjet remains good features at harmonic frequencies 2f₀ and 3f₀. In addition, we investigate the effect of an Au sphere presence in the center of the microjet on the power distribution. The results show that a spherical dark spot with a size similar to that of the Au sphere emerges in the area where the Au sphere is placed. The feature can be used to measure the size of a metallic particle.

New multiplexed system for synchronous measurement of out-of-plane deformation and two orthogonal slopes

Yonghong Wang(王永红), Xiao Zhang(张肖), Qihan Zhao(赵琪涵), Yanfeng Yao(姚彦峰), Peizheng Yan(闫佩正), and Biao Wang(王标)

Chin. Phys. B, 2022, 31 (3): 034202. DOI: 10.1088/1674-1056/ac1e10

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We propose a novel system for synchronous measurement of out-of-plane deformation and two orthogonal slopes using a single camera. The linearly polarized reference beam introduced by an optical fiber interferes with the unpolarized object beam to measure the out-of-plane deformation. A modified Mach—Zehnder interferometer is used to measure the two orthogonal slopes of the out-of-plane deformation. One of the object beams of the Mach—Zehnder interferometer is an unpolarized beam, and the other object beam is split into two orthogonal linearly polarized object beams by a polarizing prism. The two beams are orthogonally polarized. Hence, they will not interfere with each other. The two polarized beams respectively interfere with the unpolarized beam to simultaneously measure the two orthogonal slopes of the out-of-plane deformation. In addition, the imaging lens and apertures are respectively placed in three optical paths to independently control the carrier frequencies and shearing amounts. The effectiveness of this method can be proved by measuring two pressure-loaded circular plates.

High-performance and fabrication friendly polarization demultiplexer

Huan Guan(关欢), Yang Liu(刘阳), and Zhiyong Li (李智勇)

Chin. Phys. B, 2022, 31 (3): 034203. DOI: 10.1088/1674-1056/ac21bc

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A compact and fabrication friendly polarization demultiplexer (P-DEMUX) is proposed and characterized to enable wavelength-division-multiplexing and polarization-division-multiplexing simultaneously. The proposed structure is composed of a polarization-selective microring resonator in ultrathin waveguide and two bus channels in the silicon nitride-silica-silicon horizontal slot waveguides. In the slot waveguide, the transverse electric (TE) mode propagates through the silicon layer, while the transverse magnetic (TM) mode is confined in the slot region. In the designed ultra-thin waveguide, the TM mode is cut-off. The effective indexes of the TE modes for ultrathin and slot waveguides have comparable values. Thanks for these distinguishing features, the input TE mode can be efficiently filtered through the ultra-thin microring at the resonant wavelength, while the TM mode can directly output from the through port. Simulation results show that the extinction ratio of the proposed P-DEMUX for TE and TM modes are 33.21 dB and 24.97 dB, and the insertion losses are 0.346 dB and 0.324 dB, respectively, at the wavelength of 1551.64 nm. Furthermore, the device shows a broad bandwidth ($>100$ nm) for an extinction ratio (ER) of $>20$ dB. In addition, the proposed P-DEMUX also has a good fabrication tolerance for the waveguide width variation of $-20$ nm$\le \Delta w_{\rm g}\le 20$ nm and the microring width variation of $-20$ nm$\le \Delta w_{\rm r}\le $20 nm for a low insertion loss of $<0.75$ dB and low ER of $<-18$ dB.

An ultra-wideband 2-bit coding metasurface using Pancharatnam—Berry phase for radar cross-section reduction

Bao-Qin Lin(林宝勤), Wen-Zhun Huang(黄文准), Lin-Tao Lv(吕林涛), Jian-Xin Guo(郭建新),Yan-Wen Wang(王衍文), and Hong-Jun Ye(叶红军)

Chin. Phys. B, 2022, 31 (3): 034204. DOI: 10.1088/1674-1056/ac11ec

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An ultra-wideband 2-bit coding metasurface is designed for radar cross-section (RCS) reduction. The design process is presented in detail, in which a polarization conversion metasurface (PCM) is first proposed. The proposed PCM can realize ultra-wideband circular polarization (CP) maintaining reflection. Moreover, Pancharatnam—Berry (PB) phase will be generated in the co-polarized reflection coefficient by rotating the metallic patches in its unit cells. Thus, based on the PCM, the four coding elements of a 2-bit coding metasurface are constructed using PB phase, and an ultra-wideband PB 2-bit coding metasurface is proposed according to an appropriate coding sequence. The simulated and experimental results show that the coding metasurface has obvious advantages of wideband and polarization-insensitivity. Compared to a metallic plate of the same size, it can achieve more than 10 dB RCS reduction in the frequency band from 9.8 GHz to 42.6 GHz with a relative bandwidth of 125.2% under normal incidence with arbitrary polarizations.

Color-image encryption scheme based on channel fusion and spherical diffraction

Jun Wang(王君), Yuan-Xi Zhang(张沅熙), Fan Wang(王凡), Ren-Jie Ni(倪仁杰), and Yu-Heng Hu(胡玉衡)

Chin. Phys. B, 2022, 31 (3): 034205. DOI: 10.1088/1674-1056/ac1b87

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A secure encryption scheme for color images based on channel fusion and spherical diffraction is proposed in this paper. In the proposed encryption scheme, a channel fusion technology based on the discrete wavelet transformation is used to transform color images into single-channel grayscale images, firstly. In the process of transformation, the hyperchaotic system is used to permutate and diffuse the information of red—green—blue (RGB) channels to reduce the correlation of channels. Then the fused image is encrypted by spherical diffraction transform. Finally, the complex-valued diffraction result is decomposed into two real parts by the improved equal module decomposition, which are the ciphertext and the private key. Compared with the traditional color image encryption schemes that encrypt RGB channels separately, the proposed scheme is highly secure and robust.

Increasing the efficiency of post-selection in direct measurement of the quantum wave function Suggested by editors

Yong-Li Wen(温永立), Shanchao Zhang(张善超), Hui Yan(颜辉), and Shi-Liang Zhu(朱诗亮)

Chin. Phys. B, 2022, 31 (3): 034206. DOI: 10.1088/1674-1056/ac1f04

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Direct weak or strong measurement of quantum wave function based on post-selections has been widely explored; however, the efficiency of the measurement is heavily limited by the success probability of post-selection. Here we propose a modified scheme to directly measure photon's wave function by simply inserting a liquid crystal plate before the post-selection stage. Numerical simulations demonstrate that our modified method can significantly increase the efficiency of post selection. Our proposal would speed up the quantum wave function measurement with high resolution and high fidelity.

The 266-nm ultraviolet-beam generation of all-fiberized super-large-mode-area narrow-linewidth nanosecond amplifier with tunable pulse width and repetition rate

Shun Li(李舜), Ping-Xue Li(李平雪), Min Yang(杨敏), Ke-Xin Yu(于可新), Yun-Chen Zhu(朱云晨), Xue-Yan Dong(董雪岩), and Chuan-Fei Yao(姚传飞)

Chin. Phys. B, 2022, 31 (3): 034207. DOI: 10.1088/1674-1056/ac192b

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We report on a compact, stable, all-fiberized narrow-linewidth (0.045 nm) pulsed laser source emitting laser beam with a wavelength of 266 nm, and tunable pulse width and repetition rate. The system is based on all-fiberized nanosecond amplifier architecture, which consists of Yb-doped fiber preamplifiers and a super-large-mode-area Yb-doped fiber power amplifier. The fiber amplifier with a core of 50 μ is used to raise the threshold of the stimulated Brillouin scattering (SBS) effect and to obtain high output power and single pulse energy. Using lithium triborate (LBO) crystal and beta-barium borate (BBO) crystal for realizing the second-harmonic generation (SHG) and fourth-harmonic generation (FHG), we achieve 17 μJ (1.73 W) and 0.66 μJ (66 mW), respectively, at wavelengths of 532 nm and 266 nm and a repetition rate of 100 kHz with pulse width of 4 ns. This source has great potential applications in fluorescence research and solar-blind ultraviolet optical communication.

Improved thermal property of strained InGaAlAs/AlGaAs quantum wells for 808-nm vertical cavity surface emitting lasers

Zhuang-Zhuang Zhao(赵壮壮), Meng Xun(荀孟), Guan-Zhong Pan(潘冠中), Yun Sun(孙昀), Jing-Tao Zhou(周静涛), and De-Xin Wu(吴德馨)

Chin. Phys. B, 2022, 31 (3): 034208. DOI: 10.1088/1674-1056/ac16d0

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The 808-nm vertical cavity surface emitting laser (VCSEL) with strained In_0.13Ga_0.75Al_0.12As/Al_0.3Ga_0.7As quantum wells is designed and fabricated. Compared with the VCSELs with Al_0.05Ga_0.95As/Al_0.3Ga_0.7As quantum wells, the VCSEL with strained In_0.13Ga_0.75Al_0.12As/Al_0.3Ga_0.7As quantum wells is demonstrated to possess higher power conversion efficiency (PCE) and better temperature stability. The maximum PCE of 43.8% for 10-μm VCSEL is achieved at an ambient temperature of 30 ℃. The size-dependent thermal characteristics are also analyzed by characterizing the spectral power and output power. It demonstrates that small oxide-aperture VCSELs are advantageous for temperature-stable performance.

Interrogation of optical Ramsey spectrum and stability study of an ⁸⁷Sr optical lattice clock Suggested by editors

Jing-Jing Xia(夏京京), Xiao-Tong Lu(卢晓同), and Hong Chang(常宏)

Chin. Phys. B, 2022, 31 (3): 034209. DOI: 10.1088/1674-1056/ac11e0

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The optical Ramsey spectrum is experimentally realized in an ⁸⁷Sr optical lattice clock, and the measured linewidth agrees well with theoretical expectation. The coherence time between the clock laser and the atoms, which indicates the maximum free evolution period of using Ramsey detection to measure the atom-laser phase information, is determined as 340(23) ms by measuring the fringe contrasts of the Ramsey spectrum as a function of the free evolution period. Furthermore, with the same clock duty cycle of about 0.1, the clock stability is measured by using the Ramsey and Rabi spectra, respectively. The experimental and theoretical results show approximately the same stability as the two detection methods, which indicates that Ramsey detection cannot obviously improve the clock stability until the clock duty cycle is large enough. Thus, it is of great significance to choose the detection method of a specific clock.

Improving the spectral purity of single photons by a single-interferometer-coupled microring Suggested by editors

Yang Wang(王洋), Pingyu Zhu(朱枰谕), Shichuan Xue(薛诗川), Yingwen Liu(刘英文), Junjie Wu(吴俊杰), Xuejun Yang(杨学军), and Ping Xu(徐平)

Chin. Phys. B, 2022, 31 (3): 034210. DOI: 10.1088/1674-1056/ac3652

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We experimentally engineer a high-spectral-purity single-photon source using a single-interferometer-coupled silicon microring. By the reconfiguration of the interferometer, different coupling conditions can be obtained, corresponding to different quality factors for the pump and signal/idler. The ratio between the quality factor of the pump and signal/idler ranges from 0.29 to 2.57. By constructing the signal—idler joint spectral intensity, we intuitively demonstrate the spectral correlation of the signal and idler. As the ratio between the quality factor of the pump and signal/idler increases, the spectral correlation of the signal and idler decreases, i.e., the spectral purity of the signal/idler photons increases. Furthermore, time-integrated second-order correlation of the signal photons is measured, giving a value up to 94.95±3.46%. Such high-spectral-purity photons will improve the visibility of quantum interference and facilitate the development of on-chip quantum information processing.

Independently tunable dual resonant dip refractive index sensor based on metal—insulator—metal waveguide with Q-shaped resonant cavity Suggested by editors

Haowen Chen(陈颢文), Yunping Qi(祁云平), Jinghui Ding(丁京徽), Yujiao Yuan(苑玉娇), Zhenting Tian(田振廷), and Xiangxian Wang(王向贤)

Chin. Phys. B, 2022, 31 (3): 034211. DOI: 10.1088/1674-1056/ac48fe

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A plasmonic resonator system consisting of a metal—insulator—metal waveguide and a Q-shaped resonant cavity is proposed in this paper. The transmission properties of surface plasmon polaritons in this structure are investigated by using the finite difference in time domain (FDTD) method, and the simulation results contain two resonant dips. The physical mechanism is studied by the multimode interference coupled mode theory (MICMT), and the theoretical results are in highly consistent with the simulation results. Furthermore, the parameters of the Q-shaped cavity can be controlled to adjust the two dips, respectively. The refractive index sensor proposed in this paper, with a sensitivity of 1578 nm/RIU and figure of merit (FOM) of 175, performs better than most of the similar structures. Therefore, the results of the study are instructive for the design and application of high sensitivity nanoscale refractive index sensors.

Synthetical optimization of the structure dimension for the thermoacoustic regenerator

Huifang Kang(康慧芳), Lingxiao Zhang(张凌霄), Jun Shen(沈俊),Xiachen Ding(丁夏琛), Zhenxing Li(李振兴), and Jun Liu(刘俊)

Chin. Phys. B, 2022, 31 (3): 034301. DOI: 10.1088/1674-1056/ac1f02

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The quantitative investigation of parameters in the renegerator is essential for the optimization of thermoacoustic devices, while the majority of the previous research only considered parameters of the working field, working gas and the hydraulic radius. Based on the linear thermoacoustic theory, this paper extracts a normalized parameter for low-amplitude conditions, which is called the regenerator operation factor. By extracting the regenerator operation factor and relative hydraulic radius, the influence of frequency on the efficiency can be controlled and offset. It can be found that thermoacoustic devices with different frequencies can perform the same efficiency by adjusting the radius in proportion to the axial length. Finally, this paper synthetically optimizes the dimension of the thermoacoustic regenerator by taking the regenerator operation factor, relative hydraulic radius and acoustic field parameter as variables. Conclusions in this paper are of great significance for explaining the best working conditions of engines and directing the miniaturization and optimal design of thermoacoustic devices.

Nonlinear oscillation characteristics of magnetic microbubbles under acoustic and magnetic fields

Lixia Zhao(赵丽霞), Huimin Shi(史慧敏), Isaac Bello, Jing Hu(胡静), Chenghui Wang(王成会), and Runyang Mo(莫润阳)

Chin. Phys. B, 2022, 31 (3): 034302. DOI: 10.1088/1674-1056/ac1f01

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Microbubbles loaded with magnetic nanoparticles (MMBs) have attracted increasing interests in multimode imaging and drug/gene delivery and targeted therapy. However, the dynamic behaviors generated in diagnostic and therapeutic applications are not clear. In the present work, a novel theoretical model of a single MMB was developed, and the dynamic responses in an infinite viscous fluid were investigated under simultaneous exposure to magnetic and acoustic fields. The results showed that the amplitude reduces and the resonant frequency increases with the strength of the applied steady magnetic field and the susceptibility of the magnetic shell. However, the magnetic field has a limited influence on the oscillating. It is also noticed that the responses of MMB to a time-varying magnetic field is different from a steady magnetic field. The subharmonic components increase firstly and then decrease with the frequency of the magnetic field and the enhanced effect is related to the acoustic driving frequency. It is indicated that there may be a coupling interaction effect between the acoustic and magnetic fields.

High-efficiency unidirectional wavefront manipulation for broadband airborne sound with a planar device Suggested by editors

Yang Tan(谭杨), Bin Liang(梁彬), and Jianchun Cheng(程建春)

Chin. Phys. B, 2022, 31 (3): 034303. DOI: 10.1088/1674-1056/ac1e14

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In the past decade, one-way manipulation of sound has attracted rapidly growing attention with application potentials in a plethora of scenarios ranging from ultrasound imaging to noise control. Here we propose a design of a planar device capable of unidirectionally harnessing the transmitted wavefront for broadband airborne sound. Our mechanism is to use the broken spatial symmetry to give rise to different critical angles for plane waves incident along opposite directions. Along the positive direction, the incoming sound is allowed to pass with high efficiency and be arbitrarily molded into the desired shape while any reversed wave undergoes a total reflection. We analytically derive the working bandwidth and incident angle range, and present a practical implementation of our strategy. The performance of our proposed device is demonstrated both theoretically and numerically via distinct examples of production of broadband anomalous refraction, acoustic focusing and non-diffractive beams for forward transmitted wave while virtually blocking the reversed waves. Bearing advantages of simple design, planar profile, broad bandwidth and high efficiency, our design opens the possibility for novel one-way acoustic device and may have important impact on diverse applications in need of special control of airborne sound.

Mechanism analysis and improved model for stick-slip friction behavior considering stress distribution variation of interface

Jingyu Han(韩靖宇), Jiahao Ding(丁甲豪), Hongyu Wu(吴宏宇), and Shaoze Yan(阎绍泽)

Chin. Phys. B, 2022, 31 (3): 034601. DOI: 10.1088/1674-1056/ac1931

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Studying the evolution of interface contact state, revealing the "black box" behavior in interface friction and establishing a more accurate friction model are of great significance to improve the prediction accuracy of mechanical system performance. Based on the principle of total reflection, a visual analysis technology of interface contact behavior is proposed. Considering the dynamic variation of stress distribution in interface contact, we analyze the nonlinear characteristics of contact parameters in different stages of stick-slip process using the above-mentioned experimental technology. Then, we find that the tangential stiffness of the interface is not a fixed value during the stick-slip process and the stress distribution variation is one of the important factors affecting the tangential stiffness of interface. Based on the previous experimental results, we present an improved stick-slip friction model, considering the change of tangential stiffness and friction coefficient caused by the stress distribution variation. This improved model can characterize the variation characteristics of contact parameters in different stages of stick-slip process, whose simulation results are in good agreement with the experimental data. This research may be valuable for improving the prediction accuracy of mechanical system performance.

Effect of viscosity on stability and accuracy of the two-component lattice Boltzmann method with a multiple-relaxation-time collision operator investigated by the acoustic attenuation model

Le Bai(柏乐), Ming-Lei Shan(单鸣雷), Yu Yang(杨雨), Na-Na Su(苏娜娜), Jia-Wen Qian(钱佳文), and Qing-Bang Han(韩庆邦)

Chin. Phys. B, 2022, 31 (3): 034701. DOI: 10.1088/1674-1056/ac2b93

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A two-component lattice Boltzmann method (LBM) with a multiple-relaxation-time (MRT) collision operator is presented to improve the numerical stability of the single relaxation time (SRT) model. The macroscopic and the momentum conservation equations can be retrieved through the Chapman—Enskog (C-E) expansion analysis. The equilibrium moment with the diffusion term is calculated, a diffusion phenomenon is simulated by utilizing the developed model, and the numerical stability is verified. Furthermore, the binary mixture channel model is designed to simulate the sound attenuation phenomenon, and the obtained simulation results are found to be consistent with the analytical solutions. The sound attenuation model is used to study the numerical stability and calculation accuracy of the LBM model. The simulation results show the stability and accuracy of the MRT model and the SRT model under different viscosity conditions. Finally, we study the influence of the error between the macroscopic equation of the MRT model and the standard incompressible Navier—Stokes equation on the calculation accuracy of the model to demonstrate the general applicability of the conclusions drawn by the sound attenuation model in the present study.

Characterization of premixed swirling methane/air diffusion flame through filtered Rayleigh scattering

Meng Li(李猛), Bo Yan(闫博), Shuang Chen(陈爽), Li Chen(陈力), and Jin-He Mu(母金河)

Chin. Phys. B, 2022, 31 (3): 034702. DOI: 10.1088/1674-1056/ac2485

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Characteristics of a premixed, swirl methane/air diffusion flame at atmospheric pressure are measured by filtered Rayleigh scattering (FRS). Three operating conditions are investigated with the equivalence ratios of the methane/air flame covering a range of 0.67—0.83. Under each condition, single-shot and averaged FRS images over a region measured 39.3×65.6 mm² at seven cross sections of the flame are collected to demonstrate the flame behavior. A gradient calculation algorithm is applied to identify reaction zone locations and structures in the instantaneous FRS measurements. Statistical analysis for the mean FRS measurements is performed by means of joint probability density functions. The experimental results indicate that thermochemical state of the swirl flame is strongly influenced by equivalence ratio, leading to varieties of flame structures and temperature distributions. The gradient of the instantaneous FRS images clearly illustrates the characteristics of the reaction zone. The results also demonstrate that FRS can provide detailed insights into the behavior of turbulent flames.

Particle captured by a field-modulating vortex through dielectrophoresis force

Bing Yan(严兵), Bo Chen(陈波), Zerui Peng(彭泽瑞), and Yong-Liang Xiong(熊永亮)

Chin. Phys. B, 2022, 31 (3): 034703. DOI: 10.1088/1674-1056/ac248a

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In microfluidic technology, dielectrophoresis (DEP) is commonly used to manipulate particles. In this work, the fluid-particle interactions in a microfluidic system are investigated numerically by a finite difference method (FDM) for electric field distribution and a lattice Boltzmann method (LBM) for the fluid flow. In this system, efficient particle manipulation may be realized by combining DEP and field-modulating vortex. The influence of the density ($\rho_{\rm p}$), radius ($r$), and initial position of the particle in the $y$ direction ($y_{\rm p0}$), and the slip velocity ($u_{0}$) on the particle manipulation are studied systematically. It is found that compared with the particle without action of DEP force, the particle subjected to a DEP force may be captured by the vortex over a wider range of parameters. In the $y$ direction, as $\rho_{\rm p}$ or $r $ increases, the particle can be captured more easily by the vortex since it is subjected to a stronger DEP force. When $u_{0}$ is low, particle is more likely to be captured due to the vortex-particle interaction. Furthermore, the flow field around the particle is analyzed to explore the underlying mechanism. The results obtained in the present study may provide theoretical support for engineering applications of field-controlled vortices to manipulate particles.

Kinetic Alfvén waves in a deuterium-tritium fusion plasma with slowing-down distributed α-particles

Fei-Fei Lu(路飞飞) and San-Qiu Liu(刘三秋)

Chin. Phys. B, 2022, 31 (3): 035201. DOI: 10.1088/1674-1056/ac2d18

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The dispersion relation and damping rate of kinetic Alfvén waves (KAWs) in a deuterium-tritium fusion plasma with slowing-down distributed $\alpha$-particles are investigated using the kinetic theory. The variations of wave frequency and damping rate with respect to the $\alpha$ concentration (${n_{\alpha}/n_{\rm e}}$) and perpendicular wave number (${k_ \bot }$) are studied from a numerical way. The results show that the fluctuation of $\alpha$ concentration slightly affects the frequency and damping rate of KAWs at low ${n_{\alpha}/n_{\rm e}}$. In addition, the frequency and the damping rate increase as the ${k_ \bot}$ and the background temperature ${T_{\rm e}}$ increase. For comparison, the calculations are performed also in the case of $\alpha$-particles following an equivalent Maxwellian distribution. For a given ${k_ \bot }$, the value of the frequency obtained in the slowing-down distribution case is smaller than that obtained in the Maxwellian distribution case. Conversely, the value of the damping rate obtained in the slowing-down distribution case is slightly larger than that obtained in the Maxwellian distribution case.

Propagation of terahertz waves in nonuniform plasma slab under "electromagnetic window"

Hao Li(李郝), Zheng-Ping Zhang(张正平), and Xin Yang (杨鑫)

Chin. Phys. B, 2022, 31 (3): 035202. DOI: 10.1088/1674-1056/ac1b90

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The application of magnetic fields, electric fields, and the increase of the electromagnetic wave frequency are up-and-coming solutions for the blackout problem. Therefore, this study considers the influence of the external magnetic field on the electron flow and the effect of the external electric field on the electron density distribution, and uses the scattering matrix method (SMM) to perform theoretical calculations and analyze the transmission behavior of terahertz waves under different electron densities, magnetic field distributions, and collision frequencies. The results show that the external magnetic field can improve the transmission of terahertz waves at the low-frequency end. Magnetizing the plasma from the direction perpendicular to the incident path can optimize the right-hand polarized wave transmission. The external electric field can increase the transmittance to some extent, and the increase of the collision frequency can suppress the right-hand polarized wave cyclotron resonance caused by the external magnetic field. By adjusting these parameters, it is expected to alleviate the blackout phenomenon to a certain extent.

Effect of initial phase on the Rayleigh—Taylor instability of a finite-thickness fluid shell Suggested by editors

Hong-Yu Guo(郭宏宇), Tao Cheng(程涛), Jing Li(李景), and Ying-Jun Li(李英骏)

Chin. Phys. B, 2022, 31 (3): 035203. DOI: 10.1088/1674-1056/ac3390

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Rayleigh—Taylor instability (RTI) of finite-thickness shell plays an important role in deep understanding the characteristics of shell deformation and material mixing. The RTI of a finite-thickness fluid layer is studied analytically considering an arbitrary perturbation phase difference on the two interfaces of the shell. The third-order weakly nonlinear (WN) solutions for RTI are derived. It is found the main feature (bubble-spike structure) of the interface is not affected by phase difference. However, the positions of bubble and spike are sensitive to the initial phase difference, especially for a thin shell (kd<1), which will be detrimental to the integrity of the shell. Furthermore, the larger phase difference results in much more serious RTI growth, significant shell deformation can be obtained in the WN stage for perturbations with large phase difference. Therefore, it should be considered in applications where the interface coupling and perturbation phase effects are important, such as inertial confinement fusion.

Effect of the number of defect particles on the structure and dispersion relation of a two-dimensional dust lattice system Suggested by editors

Rangyue Zhang(张壤月), Guannan Shi(史冠男), Hanyu Tang(唐瀚宇), Yang Liu(刘阳), Yanhong Liu(刘艳红), and Feng Huang(黄峰)

Chin. Phys. B, 2022, 31 (3): 035204. DOI: 10.1088/1674-1056/ac306d

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The effect of the number of defect particles on the structure and dispersion relations of a two-dimensional (2D) dust lattice is studied by molecular dynamics (MD) simulation. The dust lattice structures are characterized by particle distribution, nearest neighbor configuration and pair correlation function. The current autocorrelation function, the dispersion relation and sound speed are used to represent the wave properties. The wave propagation of the dust lattice closely relates to the lattice structure. It shows that the number of defect particles can affect the dust lattice local structure and then affect the dispersion relations of waves propagating in it. The presence of defect particles has a greater effect on the transverse waves than on the longitudinal waves of the dust lattice. The appropriate number of defect particles can weaken the anisotropy property of the lattice.

Emerging of Ag particles on ZnO nanowire arrays for blue-ray hologram storage Suggested by editors

Ning Li(李宁), Xin Li(李鑫), Ming-Yue Zhang(张明越), Jing-Ying Miao(苗景迎), Shen-Cheng Fu(付申成), and Xin-Tong Zhang(张昕彤)

Chin. Phys. B, 2022, 31 (3): 036101. DOI: 10.1088/1674-1056/ac20c8

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Noble-metal/metal-oxide-semiconductor nanostructures as an important material platform have been applied in massive data storage. ZnO exhibits excellent optical modulation ability. However, plasmon induced charge separation effect in Ag/ZnO systems is very weak due to the low chemical activity on surface of the oxide. Herein, we prepare ZnO nanowire arrays via the hydrothermal method, and measure their absorption spectra, photoluminescence spectra and electron paramagnetic resonance, proving the existence of oxygen defects in ZnO. Accordingly, an idea of "electron reverse transfer" is proposed such that blue-ray (403.4 nm) induces reduction of Ag⁺ ions through the excitation of ZnO. Rod-like and spherical silver nanoparticles emerge on the surface and in the gap of ZnO nanowire arrays, respectively, after the visible light stimulus. It is found that nanowire density, oxygen defects and surface roughness are dependent on hydrothermal time. The optimized diffraction efficiency of 0.08% is obtained for reconstructing hologram in the nanocomposite film. This work provides a bright way for construction of ZnO-based optoelectronic integrated devices.

Transition state and formation process of Stone—Wales defects in graphene Suggested by editors

Jian-Hui Bai(白建会), Yin Yao(姚茵), and Ying-Zhao Jiang(姜英昭)

Chin. Phys. B, 2022, 31 (3): 036102. DOI: 10.1088/1674-1056/ac20c5

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Stone—Wales (SW) defects are possibly formed in graphene and other two-dimensional materials, and have multiple influence on their physical and chemical properties. In this study, the transition state of SW defects in graphene is determined with the fully discrete Peierls theory. Furthermore, the atomic formation process is investigated by means of ab-initio simulations. The atomic structure change and energetics of the SW transformation are revealed. It is found that the transition state is at the SW bond rotation of 34.5° and the activation energy barrier is about 12 eV. This work provides a new method to investigate SW transformations in graphene-like materials and to explore unknown SW-type defects in other 2D materials.

Effect of heavy ion irradiation on the interface traps of AlGaN/GaN high electron mobility transistors Suggested by editors

Zheng-Zhao Lin(林正兆), Ling Lü(吕玲), Xue-Feng Zheng(郑雪峰), Yan-Rong Cao(曹艳荣), Pei-Pei Hu(胡培培), Xin Fang(房鑫), and Xiao-Hua Ma(马晓华)

Chin. Phys. B, 2022, 31 (3): 036103. DOI: 10.1088/1674-1056/ac11e4

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AlGaN/GaN high electron mobility transistors (HEMTs) were irradiated with heavy ions at various fluences. After irradiation by 2.1 GeV¹⁸¹ Ta³²⁺ ions, the electrical characteristics of the devices significantly decreased. The threshold voltage shifted positively by approximately 25% and the saturation currents decreased by approximately 14%. Defects were induced in the band gap and the interface between the gate and barrier acted as tunneling sites, which increased the gate current tunneling probability. According to the pulsed output characteristics, the amount of current collapse significantly increased and more surface state traps were introduced after heavy ion irradiation. The time constants of the induced surface traps were mainly less than 10 μs.

First-principles study of stability of point defects and their effects on electronic properties of GaAs/AlGaAs superlattice Suggested by editors

Shan Feng(冯山), Ming Jiang(姜明), Qi-Hang Qiu(邱启航), Xiang-Hua Peng(彭祥花), Hai-Yan Xiao(肖海燕), Zi-Jiang Liu(刘子江), Xiao-Tao Zu(祖小涛), and Liang Qiao(乔梁)

Chin. Phys. B, 2022, 31 (3): 036104. DOI: 10.1088/1674-1056/ac16cb

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When the GaAs/AlGaAs superlattice-based devices are used under irradiation environments, point defects may be created and ultimately deteriorate their electronic and transport properties. Thus, understanding the properties of point defects like vacancies and interstitials is essential for the successful application of semiconductor materials. In the present study, first-principles calculations are carried out to explore the stability of point defects in GaAs/Al_0.5Ga_0.5As superlattice and their effects on electronic properties. The results show that the interstitial defects and Frenkel pair defects are relatively difficult to form, while the antisite defects are favorably created generally. Besides, the existence of point defects generally modifies the electronic structure of GaAs/Al_0.5Ga_0.5As superlattice significantly, and most of the defective SL structures possess metallic characteristics. Considering the stability of point defects and carrier mobility of defective states, we propose an effective strategy that Al_As, Ga_As, and Al_Ga antisite defects are introduced to improve the hole or electron mobility of GaAs/Al_0.5Ga_0.5As superlattice. The obtained results will contribute to the understanding of the radiation damage effects of the GaAs/AlGaAs superlattice, and provide a guidance for designing highly stable and durable semiconductor superlattice-based electronics and optoelectronics for extreme environment applications.

Boron at tera-Pascal pressures

Peiju Hu(胡佩菊), Junhao Peng(彭俊豪), Xing Xie(谢兴), Minru Wen(文敏儒),Xin Zhang(张欣), Fugen Wu(吴福根), and Huafeng Dong(董华锋)

Chin. Phys. B, 2022, 31 (3): 036301. DOI: 10.1088/1674-1056/ac11e6

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The study of boron structure is fascinating because boron has various allotropes containing boron icosahedrons under pressure. Here, we propose a new boron structure (space group $Fm\overline{3}m$) that is dynamically stable at 1.4 tera-Pascal (TPa) using density functional theory and an evolutionary algorithm. The unit cell of this structure can be viewed as a structure with a boron atom embedded in the icosahedron. This structure behaves as a metal, and cannot be stable under ambient pressure. Furthermore, we found electrons gather in lattice interstices, which is similar to that of the semiconductor Na or Ca$_{2}$N-II under high pressure. The discovery of this new structure expands our comprehension of high-pressure condensed matter and contributes to the further development of high-pressure science.

Solid-liquid transition induced by the anisotropic diffusion of colloidal particles

Fu-Jun Lin(蔺福军), Jing-Jing Liao(廖晶晶), Jian-Chun Wu(吴建春), and Bao-Quan Ai(艾保全)

Chin. Phys. B, 2022, 31 (3): 036401. DOI: 10.1088/1674-1056/ac1e19

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We numerically study the phase behaviors of colloids with anisotropic diffusion in two dimensions. It is found that the diffusion anisotropy of colloidal particles plays an important role in the phase transitions. A strong diffusion anisotropy induces the large vibration of particles, subsequently, the system goes into a disordered state. In the presence of the strong-coupling, particles with weak diffusion anisotropy can freeze into hexagonal crystals. Thus, there exists a solid-liquid transition. With the degree of diffusion anisotropy increasing, the transition points are shifted to the stronger-coupled region. A competition between the degree of diffusion anisotropy and coupling strength widens the transition region where the heterogeneous structures coexist, which results in a broad-peak probability distribution curve for the local order parameter. Our study may be helpful for the experiments related to the phase behavior in statistical physics, materials science and biophysical systems.

Effect of an electric field on dewetting transition of nitrogen-water system Suggested by editors

Qi Feng(冯琦), Jiaxian Li(厉嘉贤), Xiaoyan Zhou(周晓艳), and Hangjun Lu(陆杭军)

Chin. Phys. B, 2022, 31 (3): 036801. DOI: 10.1088/1674-1056/ac1e21

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We investigate the influence of an external electric field on the dewetting behavior of nitrogen-water systems between two hydrophobic plates using molecular dynamics simulations. It is found that the critical distance of dewetting increases obviously with the electric field strength, indicating that the effective range of hydrophobic attraction is extended. The mechanism behind this interesting phenomenon is related to the rearrangement of hydrogen bond networks between water molecules induced by the external electric field. Changes in the hydrogen bond networks and in the dipole orientation of the water molecules result in the redistribution of the neutral nitrogen molecules, especially in the region close to the hydrophobic plates. Our findings may be helpful for understanding the effects of the electric field on the long-range hydrophobic interactions.

High-energy x-ray diffraction study on phase transition asymmetry of plastic crystal neopentylglycol

Zhe Zhang(张哲), Yan-Na Chen(陈艳娜), Ji Qi(齐迹), Zhao Zhang(张召), Koji Ohara, Osami Sakata, Zhi-Dong Zhang(张志东), and Bing Li(李昺)

Chin. Phys. B, 2022, 31 (3): 036802. DOI: 10.1088/1674-1056/ac140c

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As a prototype material of colossal barocaloric effects, neopentylglycol is investigated by combining high-precision differential scanning calorimetric measurement and high-energy x-ray diffraction measurement. The diffraction data at constant temperatures indicate a first-order phase transition with thermal hysteresis as well as the phase transition asymmetry, specifically, the phase transition is completed faster at cooling than at heating. The analysis of resulting pair distribution function confirms the intermolecular disorder in the high-temperature phase. The phase transition asymmetry is quantitatively characterized by time-resolved x-ray diffraction, which is in agreement with the thermal measurement. Also, such an asymmetry is observed to be suppressed at high pressures.

Mode characteristics of nested eccentric waveguides constructed by two cylindrical nanowires coated with graphene

Ji Liu(刘吉), Lixia Yu(于丽霞), and Wenrui Xue(薛文瑞)

Chin. Phys. B, 2022, 31 (3): 036803. DOI: 10.1088/1674-1056/ac1e17

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A kind of nested eccentric waveguide constructed with two cylindrical nanowires coated with graphene was designed. The mode characteristics of this waveguide were studied using the multipole method. It was found that the three lowest modes (mode 0, mode 1 and mode 2) can be combined by the zero-order mode or/and the first-order modes of two single nanowires. Mode 0 has a higher figure of merit and the best performance among these modes within the parameter range of interest. The mode characteristics can be adjusted by changing the parameters of the waveguide. For example, the propagation length will be increased when the operating wavelength, the minimum spacing between the inner and outer cylinders, the inner cylinder radius and the Fermi energy are increased. However, when the outer cylinder radius, the dielectric constants of region I, or the dielectric constants of region III are increased, the opposite effect can be seen. These results are consistent with the results obtained using the finite element method (FEM). The waveguide structure designed in this paper is easy to fabricate and can be applied to the field of micro/nano sensing.

Electronic structure and spin–orbit coupling in ternary transition metal chalcogenides Cu₂TlX₂ (X = Se, Te) ^Hot!

Na Qin(秦娜), Xian Du(杜宪), Yangyang Lv(吕洋洋), Lu Kang(康璐), Zhongxu Yin(尹中旭), Jingsong Zhou(周景松), Xu Gu(顾旭), Qinqin Zhang(张琴琴), Runzhe Xu(许润哲), Wenxuan Zhao(赵文轩), Yidian Li(李义典), Shuhua Yao(姚淑华), Yanfeng Chen(陈延峰), Zhongkai Liu(柳仲楷), Lexian Yang(杨乐仙), and Yulin Chen(陈宇林)

Chin. Phys. B, 2022, 31 (3): 037101. DOI: 10.1088/1674-1056/ac3ecd

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Ternary transition metal chalcogenides provide a rich platform to search and study intriguing electronic properties. Using angle-resolved photoemission spectroscopy and ab initio calculation, we investigate the electronic structure of Cu$_{2}$Tl$X_{2}$ ($X=\text{Se, Te}$), ternary transition metal chalcogenides with quasi-two-dimensional crystal structure. The band dispersions near the Fermi level are mainly contributed by the Te/Se p orbitals. According to our ab-initio calculation, the electronic structure changes from a semiconductor with indirect band gap in Cu$_{2}$TlSe$_{2}$ to a semimetal in Cu$_{2}$TlTe$_{2}$, suggesting a band-gap tunability with the composition of Se and Te. By comparing ARPES experimental data with the calculated results, we identify strong modulation of the band structure by spin-orbit coupling in the compounds. Our results provide a ternary platform to study and engineer the electronic properties of transition metal chalcogenides related to large spin-orbit coupling.

Intrinsic V vacancy and large magnetoresistance in V_1-δSb₂ single crystal ^Hot!

Yong Zhang(张勇), Xinliang Huang(黄新亮), Jinglei Zhang(张警蕾), Wenshuai Gao(高文帅), Xiangde Zhu(朱相德), and Li Pi(皮雳)

Chin. Phys. B, 2022, 31 (3): 037102. DOI: 10.1088/1674-1056/ac3070

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The binary pnictide semimetals have attracted considerable attention due to their fantastic physical properties that include topological effects, negative magnetoresistance, Weyl fermions, and large non-saturation magnetoresistance. In this paper, we have successfully grown the high-quality V_1-δSb₂ single crystals by Sb flux method and investigated their electronic transport properties. A large positive magnetoresistance that reaches 477% under a magnetic field of 12 T at T = 1.8 K was observed. Notably, the magnetoresistance showed a cusp-like feature at the low magnetic fields and such feature weakened gradually as the temperature increased, which indicated the presence of a weak antilocalization effect (WAL). In addition, based upon the experimental and theoretical band structure calculations, V_1-δSb₂ is a research candidate for a flat band.

Growth, characterization, and Raman spectra of the 1T phases of TiTe₂, TiSe₂, and TiS₂ Suggested by editors

Xiao-Fang Tang(唐筱芳), Shuang-Xing Zhu(朱双兴), Hao Liu(刘豪), Chen Zhang(章晨), Qi-Yi Wu(吴旗仪), Zi-Teng Liu(刘子腾), Jiao-Jiao Song(宋姣姣), Xiao Guo(郭晓), Yong-Song Wang(王永松), He Ma(马赫), Yin-Zou Zhao(赵尹陬), Fan-Ying Wu(邬钒颖), Shu-Yu Liu(刘姝妤), Kai-Hui Liu(刘开辉), Ya-Hua Yuan(袁亚华), Han Huang(黄寒), Jun He(何军), Wen Xu(徐文), Hai-Yun Liu(刘海云), Yu-Xia Duan(段玉霞), and Jian-Qiao Meng(孟建桥)

Chin. Phys. B, 2022, 31 (3): 037103. DOI: 10.1088/1674-1056/ac306a

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High-quality large 1$T$ phase of Ti$X_2$ ($X ={\rm Te}$, Se, and S) single crystals have been grown by chemical vapor transport using iodine as a transport agent. The samples are characterized by compositional and structural analyses, and their properties are investigated by Raman spectroscopy. Several phonon modes have been observed, including the widely reported $A_{1g}$ and $E_g$ modes, the rarely reported $E_u$ mode ($\sim$183 cm$^{-1}$ for TiTe$_2$, and $\sim$185 cm$^{-1}$ for TiS$_2$), and even the unexpected $K$ mode ($\sim$85 cm$^{-1}$) of TiTe$_2$. Most phonons harden with the decrease of temperature, except that the $K$ mode of TiTe$_2$ and the $E_u$ and "$A_{2u}$/Sh" modes of TiS$_2$ soften with the decrease of temperature. In addition, we also found phonon changes in TiSe$_2$ that may be related to charge density wave phase transition. Our results on Ti$X_2$ phonons will help to understand their charge density wave and superconductivity.

High-throughput computational material screening of the cycloalkane-based two-dimensional Dion—Jacobson halide perovskites for optoelectronics

Guoqi Zhao(赵国琪), Jiahao Xie(颉家豪), Kun Zhou(周琨), Bangyu Xing(邢邦昱), Xinjiang Wang(王新江), Fuyu Tian(田伏钰), Xin He(贺欣), and Lijun Zhang(张立军)

Chin. Phys. B, 2022, 31 (3): 037104. DOI: 10.1088/1674-1056/ac4036

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Two-dimensional (2D) layered perovskites have emerged as potential alternates to traditional three-dimensional (3D) analogs to solve the stability issue of perovskite solar cells. In recent years, many efforts have been spent on manipulating the interlayer organic spacing cation to improve the photovoltaic properties of Dion—Jacobson (DJ) perovskites. In this work, a serious of cycloalkane (CA) molecules were selected as the organic spacing cation in 2D DJ perovskites, which can widely manipulate the optoelectronic properties of the DJ perovskites. The underlying relationship between the CA interlayer molecules and the crystal structures, thermodynamic stabilities, and electronic properties of 58 DJ perovskites has been investigated by using automatic high-throughput workflow cooperated with density-functional (DFT) calculations. We found that these CA-based DJ perovskites are all thermodynamic stable. The sizes of the cycloalkane molecules can influence the degree of inorganic framework distortion and further tune the bandgaps with a wide range of 0.9—2.1 eV. These findings indicate the cycloalkane molecules are suitable as spacing cation in 2D DJ perovskites and provide a useful guidance in designing novel 2D DJ perovskites for optoelectronic applications.

Magnetic proximity effect induced spin splitting in two-dimensional antimonene/Fe₃GeTe₂ van der Waals heterostructures ^Hot!

Xiuya Su(苏秀崖), Helin Qin(秦河林), Zhongbo Yan(严忠波), Dingyong Zhong(钟定永), and Donghui Guo(郭东辉)

Chin. Phys. B, 2022, 31 (3): 037301. DOI: 10.1088/1674-1056/ac16c8

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Recently, two-dimensional van der Waals (vdW) magnetic heterostructures have attracted intensive attention since they can show remarkable properties due to the magnetic proximity effect. In this work, the spin-polarized electronic structures of antimonene/Fe₃GeTe₂ vdW heterostructures were investigated through the first-principles calculations. Owing to the magnetic proximity effect, the spin splitting appears at the conduction-band minimum (CBM) and the valence-band maximum (VBM) of the antimonene. A low-energy effective Hamiltonian was proposed to depict the spin splitting. It was found that the spin splitting can be modulated by means of applying an external electric field, changing interlayer distance or changing stacking configuration. The spin splitting energy at the CBM monotonously increases as the external electric field changes from -5 V/nm to 5 V/nm, while the spin splitting energy at the VBM almost remains the same. Meanwhile, as the interlayer distance increases, the spin splitting energies at the CBM and VBM both decrease. The different stacking configurations can also induce different spin splitting energies at the CBM and VBM. Our work demonstrates that the spin splitting of antimonene in this heterostructure is not singly dependent on the nearest Sb—Fe distance, which indicates that magnetic proximity effect in heterostructures may be modulated by multiple factors, such as hybridization of electronic states and the local electronic environment. The results enrich the fundamental understanding of the magnetic proximity effect in two-dimensional vdW heterostructures.

Entanglement spectrum of non-Abelian anyons Suggested by editors

Ying-Hai Wu(吴英海)

Chin. Phys. B, 2022, 31 (3): 037302. DOI: 10.1088/1674-1056/ac280d

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Non-Abelian anyons can emerge as fractionalized excitations in two-dimensional systems with topological order. One important example is the Moore—Read fractional quantum Hall state. Its quasihole states are zero-energy eigenstates of a parent Hamiltonian, but its quasiparticle states are not. Both of them can be modeled on an equal footing using the bipartite composite fermion method. We study the entanglement spectrum of the cases with two or four non-Abelian anyons. The counting of levels in the entanglement spectrum can be understood using the edge theory of the Moore—Read state, which reflects the topological order of the system. It is shown that the fusion results of two non-Abelian anyons is determined by their distributions in the bipartite construction.

Surface modulation of halide perovskite films for efficient and stable solar cells

Qinxuan Dai(戴沁煊), Chao Luo(骆超), Xianjin Wang(王显进), Feng Gao(高峰), Xiaole Jiang(姜晓乐), and Qing Zhao(赵清)

Chin. Phys. B, 2022, 31 (3): 037303. DOI: 10.1088/1674-1056/ac1fe0

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As the main distribution place of deep-level defects and the entrance of water, the interface is critical to determining both the power conversion efficiency (PCE) and the stability of perovskite solar cells (PSCs). Suitable interface design can dramatically passivate interface defects and optimize energy level alignment for suppressing the nonradiative recombination and effectively extracting the photogenerated carriers towards higher PCE. Meanwhile, a proper interface design can also block the interface diffusion of ions for high operational stability. Therefore, interface modification is of great significance to make the PSCs more efficient and stable. Upon optimized material choices, the three-dimensional halide perovskite graded junction layer, low-dimensional halide perovskite interface layer and organic salt passivation layer have been constructed on perovskite films for superior PSCs, yet a systematic review of them is missing. Thus, a guide and summary of recent advances in modulating the perovskite films interface is necessary for the further development of more efficient interface modification.

First principles study on geometric and electronic properties of two-dimensional Nb₂CT_x MXenes Suggested by editors

Guoliang Xu(徐国亮), Jing Wang(王晶), Xilin Zhang(张喜林), and Zongxian Yang(杨宗献)

Chin. Phys. B, 2022, 31 (3): 037304. DOI: 10.1088/1674-1056/ac322e

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MXenes are a new type of two-dimensional carbides with rich physical and chemical properties. The physics of MXenes, and thus the applications, are dominated by surface functional groups. Herein, the effects of different terminations (O, S, Se, Te) on the geometric and electronic properties of Nb₂C MXenes were studied via density functional theory (DFT) calculations. Three adsorption sites were examined to determine the most stable configurations. The results showed that both the types and the positions of surface functional groups influence the geometric stability and physical characters of Nb₂C. The S and Se terminations make the Nb₂C MXenes to be semiconductor, while Nb₂C MXenes with other terminations (O, Te) are conductor. The electron location function, density of states, Bader charge distribution, and the projected crystal orbital Hamilton population were conducted to explain the origin of adsorption stability and electronic nature difference. Our results provide a fundamental understanding about the effects of surface terminations on the intrinsic stability and electronic properties of Nb₂C MXenes.

Spin—orbit stable dirac nodal line in monolayer B₆O

Wen-Rong Liu(刘文荣), Liang Zhang(张亮), Xiao-Jing Dong(董晓晶), Wei-Xiao Ji(纪维霄), Pei-Ji Wang(王培吉), and Chang-Wen Zhang(张昌文)

Chin. Phys. B, 2022, 31 (3): 037305. DOI: 10.1088/1674-1056/ac4cba

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The two-dimensional (2D) materials with nodal line band crossing have been attracting great research interest. However, it remains a challenge to find high-stable nodal line structure in 2D systems. Herein, based on the first-principles calculations and theoretical analysis, we propose that monolayer B₆O possesses symmetry protected Dirac nodal line (DNL) state, with its Fermi velocity of 10⁶ m/s in the same order of magnitude as that of graphene. The origin of DNL fermions is induced by coexistence of time-reversal symmetry and inversion symmetry. A two-band tight-binding model is further given to understand the mechanism of DNL. Considering its robustness against spin—orbit coupling (SOC) and high structural stability, these results suggest monolayer B₆O as a new platform for realizing future high-speed low-dissipation devices.

Electronic properties and interfacial coupling in Pb islands on single-crystalline graphene

Jing-Peng Song(宋靖鹏) and Ang Li(李昂)

Chin. Phys. B, 2022, 31 (3): 037401. DOI: 10.1088/1674-1056/ac1b8e

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Introducing metal thin films on two-dimensional (2D) material may present a system to possess exotic properties due to reduced dimensionality and interfacial effects. We deposit Pb islands on single-crystalline graphene on a Ge(110) substrate and studied the nano- and atomic-scale structures and low-energy electronic excitations with scanning tunneling microscopy/spectroscopy (STM/STS). Robust quantum well states (QWSs) are observed in Pb(111) islands and their oscillation with film thickness reveals the isolation of free electrons in Pb from the graphene substrate. The spectroscopic characteristics of QWSs are consistent with the band structure of a free-standing Pb(111) film. The weak interface coupling is further evidenced by the absence of superconductivity in graphene in close proximity to the superconducting Pb islands. Accordingly, the Pb(111) islands on graphene/Ge(110) are free-standing in nature, showing very weak electronic coupling to the substrate.

Induced current of high temperature superconducting loops by combination of exciting coil and thermal switch Suggested by editors

Jia-Wen Wang(王佳雯), Yin-Shun Wang(王银顺), Hua Chai(柴华), Ling-Feng Zhu(祝凌峰), and Wei Pi(皮伟)

Chin. Phys. B, 2022, 31 (3): 037402. DOI: 10.1088/1674-1056/ac1f0a

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With its commercialization, the second-generation (2G) high temperature superconducting (HTS) RE—Ba—Cu—O (REBCO, RE is rare earth) tape is extensively applied to the superconducting magnets in the high magnetic fields. However, unlike low temperature superconducting (LTS) magnets, the HTS magnet cannot operate in the persistent current mode (PCM) due to the immature superconducting soldering technique. In this paper, an exciting method for two HTS sub-loops, so-called charging and load loops, is proposed by flux pump consisting of exciting coil and controllable thermal switch. Two HTS sub-loops are made of an REBCO tape with two slits. An exciting coil with iron core is located in one sub-loop and is supplied with a triangular waveform current so that magnetic field is generated in another sub-loop. The influence of magnetic flux on induced current in load loop is presented and verified in experiment at 77 K. The relationship between the induced magnetic flux density and the current on the sub-loops having been calibrated, magnetic flux density, and induced current are obtained. The results show that the HTS sub-loops can be excited by a coil with thermal switch and the induced current increases with magnetic flux of exciting coil increasing, which is promising for persistent current operation mode of HTS magnets.

On the origin of the anomalous sign reversal in the Hall effect in Nb thin films Suggested by editors

Dan Zhou(周丹), Han-Song Zeng(曾寒松), Rujun Tang(汤如俊), Zhihong Hang(杭志宏), Zhiwei Hu(胡志伟), Zixi Pei(裴子玺), and Xinsheng Ling(凌新生)

Chin. Phys. B, 2022, 31 (3): 037403. DOI: 10.1088/1674-1056/ac3ba8

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We re-visit the anomalous sign reversal problem in the Hall effect of the sputtered Nb thin films. We find that the anomalous sign reversal in the Hall effect is extremely sensitive to a small tilting of the magnetic field and to the magnitude of the applied current. Large anomalous variations are also observed in the symmetric part of the transverse resistance R_xy. We suggest that the surface current loops on superconducting grains at the edges of the superconducting thin films may be responsible for the Hall sign reversal and the accompanying anomalous effects in the symmetric part of R_xy.

Dynamic vortex Mott transition in triangular superconducting arrays

Zi-Xi Pei(裴子玺), Wei-Gui Guo(郭伟贵), and Xiang-Gang Qiu(邱祥冈)

Chin. Phys. B, 2022, 31 (3): 037404. DOI: 10.1088/1674-1056/ac3cb1

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The proximity-coupled superconducting island arrays on a metallic film provide an ideal platform to study the phase transition of vortex states under mutual interactions between the vortex and potential landscape. We have developed a top-down microfabrication process for Nb island arrays on Au film by employing an Al hard mask. A current-induced dynamic vortex Mott transition has been observed under the perpendicular magnetic fields of $f$ magnetic flux quantum per unit cell, which is characterized by a dip-to-peak reversal in differential resistance d$V$/d$I$ vs. $f$ curve with the increasing current. The d$V$/d$I$ vs. $I$ characteristics show a scaling behavior near the magnetic fields of $f= {1}/{2}$ and $f=1$, with the critical exponents $\varepsilon$ of 0.45 and 0.3, respectively, suggesting different universality classes at these two fields.

Wire network behavior of superconducting films with lower symmetrical mesoscopic hole arrays Suggested by editors

Wei-Gui Guo(郭伟贵), Zi-Xi Pei(裴子玺), and Xiang-Gang Qiu(邱祥冈)

Chin. Phys. B, 2022, 31 (3): 037405. DOI: 10.1088/1674-1056/ac43af

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Superconducting films with the same hole density but different geometric symmetry have been designed and fabricated. The R(H) curves show obvious periodic oscillations with several dips at fractional matching fields. It is found that the period of the oscillations in the low field is not necessary equal to that derived from the hole density, but consistent with that from the corresponding wire networks when the large disk-like film regions are regarded as nodes. The experimental results of R(H), T_c(H) and j_c(H) at fractional matching fields within the first oscillation also support the rationality of considering films with large-diametered hole arrays as wire networks. Our results demonstrate that the connectivity of superconducting films with large-diametered hole arrays plays a more important role in the oscillations of R(H) curves.

Superconductivity in CuIr_2-xAl_xTe₄ telluride chalcogenides Suggested by editors

Dong Yan(严冬), Lingyong Zeng(曾令勇), Yijie Zeng(曾宜杰), Yishi Lin(林一石), Junjie Yin(殷俊杰), Meng Wang(王猛), Yihua Wang(王熠华), Daoxin Yao(姚道新), and Huixia Luo(罗惠霞)

Chin. Phys. B, 2022, 31 (3): 037406. DOI: 10.1088/1674-1056/ac43b1

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The relationship between charge-density-wave (CDW) and superconductivity (SC), two vital physical phases in condensed matter physics, has always been the focus of scientists' research over the past decades. Motivated by this research hotspot, we systematically studied the physical properties of the layered telluride chalcogenide superconductors CuIr$_{2-x}$Al$_{x}$Te$_{4}$ ($0 \leqslant x \leqslant 0.2$). Through the resistance and magnetization measurements, we found that the CDW order was destroyed by a small amount of Al doping. Meanwhile, the superconducting transition temperature ($T_{\rm c}$) kept changing with the change of doping amount and rose towards the maximum value of 2.75 K when $x=0.075$. The value of normalized specific heat jump ($\Delta C/\gamma T_{\rm c}$) for the highest $T_{\rm c}$ sample CuIr$_{1.925}$Al$_{0.075}$Te$_{4}$ was 1.53, which was larger than the BCS value of 1.43 and showed the bulk superconducting nature. In order to clearly show the relationship between SC and CDW states, we propose a phase diagram of $T_{\rm c}$ vs. doping content.

A review on 3d transition metal dilute magnetic REIn₃ intermetallic compounds

Xin-Peng Guo(郭新鹏), Yong-Quan Guo(郭永权), Lin-Han Yin(殷林瀚), and Qiang He(何强)

Chin. Phys. B, 2022, 31 (3): 037501. DOI: 10.1088/1674-1056/ac20cd

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The dilute magnetic intermetallic compound (DMIC) is an extended study of the dilute magnetic semiconductor. The giant magnetic effect and room temperature ferromagnetism are induced by doping minor 3d transition metal into REIn₃ intermetallic compound. Owing to the metallic processability, the REIn₃-based DMIC might have the potential application as magnetoelectric device. In this review, the structural stability, magnetic and electric transport properties of REIn_3-xT_x (RE=rare earth; T=Co, Mn, Fe; x=0—0.3) have been systematically summarized and analyzed.

High-pressure Raman study of osmium and rhenium up to 200 GPa and pressure dependent elastic shear modulus C₄₄ Suggested by editors

Jingyi Liu(刘静仪), Yu Tao(陶雨), Chunmei Fan(范春梅), Binbin Wu(吴彬彬), Qiqi Tang(唐琦琪), and Li Lei(雷力)

Chin. Phys. B, 2022, 31 (3): 037801. DOI: 10.1088/1674-1056/ac1eff

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High-pressure Raman scattering from hexagonal close-packed (HCP) metals Os and Re have been extended up to 200 GPa, and the pressure-dependent shear modulus C₄₄ has been deduced from the Raman-active mode E_2g, which is generated from the adjacent vibration of atoms in hexagonal planes, providing the valuable information about the elastic properties for HCP metals under high pressure. Combined with the available data of HCP metals from previous works, a further study indicates that the $C_{44}^\prime/C_{44}$ ratio would be close to a constant value, 0.01, with increasing atomic number of metals. The results obtained from high-pressure Raman scattering will allow us to probe the elastic anisotropy of the HCP metals at very high pressure.

Enhancing the photo-luminescence stability of CH₃NH₃PbI₃ film with ionic liquids ^Hot!

Weifeng Ma(马威峰), Chunjie Ding(丁春杰), Nasrullah Wazir, Xianshuang Wang(王宪双), Denan Kong(孔德男), An Li(李安), Bingsuo Zou(邹炳锁), and Ruibin Liu(刘瑞斌)

Chin. Phys. B, 2022, 31 (3): 037802. DOI: 10.1088/1674-1056/ac3067

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The methylammonium lead triiodide (CH₃NH₃PbI₃)-based perovskite shows a great alluring prospect in areas of solar cells, lasers, photodetectors, and light emitting diodes owing to their excellent optical and electrical advantages. However, it is very sensitive to the surrounding oxygen and moisture, which limits its development seriously. It is urgent to spare no effort to enhance its optical and electrical stability for further application. In this paper, we synthesize the MAPbI₃ perovskite film on the glass substrate with/without the ionic liquid (IL) of 1-Butyl-3-methylimidazolium tetrafluoroborate (BMIMBF₄) by a simple two-step sequential solution method. The additive of BMIMBF₄ can improve the quality of crystal structure. Moreover, the photo-luminescence (PL) intensity of MAPbI₃ film with BMIMBF₄ is much stronger than the pure MAPbI₃ film after a week in the air, which is almost ten-fold of the pure one. Meanwhile, under the illumination of 405-nm continuous wave (CW) laser, the fluorescent duration of the MAPbI₃ film with BMIMBF₄ is approximately 2.75 min, while the pure MAPbI₃ film is only about 6 s. In fact, ionic liquid of BMIMBF₄ in the perovskite film plays a role of passivation, which prevents the dissolution of MAPbI₃ into CH₃NH₃ and PbI₂ and thus enhances the stability of environment. In addition, the ionic liquid of BMIMBF₄ possesses high ionic conductivity, which accelerates the electron transport, so it is beneficial for the perovskite film in the areas of solar cells, photodetectors, and lasers. This interesting experiment provides a promising way to develop the perovskite's further application.

Surface-enhanced fluorescence and application study based on Ag-wheat leaves

Hongwen Cao(曹红文), Liting Guo(郭立婷), Zhen Sun(孙祯), Tifeng Jiao(焦体峰), and Mingli Wang(王明利)

Chin. Phys. B, 2022, 31 (3): 037803. DOI: 10.1088/1674-1056/ac1f0d

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Wheat leaves with natural microstructures as substrates were covered by the silver nanoislands by magnetron to prepare a low-cost, environment-friendly and mass production surface-enhanced fluorescence (SEF) substrate (Ag-WL substrate). The best SEF substrate was selected by repeatly certifying the fluorescence intensity of 10^-5 M Rhodamine B (RB) and 10^-5 M Rhodamine 6G (R6G) aqueous solutions. The abundant semi-spherical protrusions and flake-like structures on the surface of the Ag-WL substrate produce high-density hot spots, which provides a new and simple idea for the preparation of biomimetic materials. The results of 3D finite-different time-domain (FDTD) simulation show that the nanoisland gap of semi-spherical protrusions and flake-like structures has produced rich hotspots. By adjusting the time of magnetron sputtering, the enhancement factor (EF) was as high as 839 times, relative standard deviation (RSD) reached as low as 10.7%, and the substrate was very stable and repeatable, which shows that Ag-WL substrate is trustworthy. Moreover, semi-spherical protrusions provide stronger surface-enhanced Raman scattering (SERS) effects compared to flake-like structure. What is more surprising is that the detection limit of the substrate for toxic substance crystal violet (CV) is as low as 10^-10 M.

A flexible ultra-broadband metamaterial absorber working on whole K-bands with polarization-insensitive and wide-angle stability

Tao Wang(汪涛), He-He He(何贺贺), Meng-Di Ding(丁梦迪), Jian-Bo Mao(毛剑波), Ren Sun(孙韧), and Lei Sheng(盛磊)

Chin. Phys. B, 2022, 31 (3): 037804. DOI: 10.1088/1674-1056/ac306e

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For potential military applications, a flexible metamaterial absorber (MMA) working on whole K-bands with total-thickness of 3.367 mm, ultra-broadband, polarization-insensitive, and wide-angle stability is presented based on frequency-selective surface (FSS). The absorber is composed of polyvinyl chloride (PVC) layer, polyimide (PI) layer, and poly tetra fluoro ethylene (PTFE) layer, with a sandwich structure of PVC-PI-PTFE-metal plate. Periodic conductive patterns play a crucial role in the absorber, and in traditional, it is designed on the upper surface of PI layer to form LC resonance. Different from commonly absorber, all the patterns are located on the lower surface of the PI layer in this work, and hence the impedance matching and absorptivity are improved in this purposed absorber. The flexible absorber with patterns on lower surface of the PI layer is compared with that on upper surface of the PI layer, the difference and the reasons are explained by absorption mechanism based on equivalent circuit model, and surface current density and electric field distribution are used to analyze resonance peaks. Absorptivity is greater than 90% in a frequency range of 10.47 GHz-45.44 GHz with relative bandwidth of 125.1%, covering the whole Ku, K, Ka, and some of X, U bands, especially containing the whole K bands from 12 GHz to 40 GHz. Radar cross section (RCS) is reduced at least 10 dB in 11.48 GHz-43.87 GHz frequency ranges, and absorption remained about 90% when the incident angle changed from 0° to 55°. The purposed absorber is fabricated, measured, and experiment results show good agreement with theoretical analysis and numerical simulation. After bonded on outer surface of different cylinders with diameters of 200 mm and 100 mm, the absorption of MMA is approximately reduced 10% and 20% respectively, which shows good conformal character with surface of various curvatures. Due to the attractive performance on strong absorption in the whole K-bands, flexible and easy conformal, our design exhibits broad potential application in radar stealth and sensors.

A high-quality-factor ultra-narrowband perfect metamaterial absorber based on monolayer molybdenum disulfide

Liying Jiang(蒋黎英), Yingting Yi(易颖婷), Yijun Tang(唐轶峻), Zhiyou Li(李治友),Zao Yi(易早), Li Liu(刘莉), Xifang Chen(陈喜芳), Ronghua Jian(简荣华),Pinghui Wu(吴平辉), and Peiguang Yan(闫培光)

Chin. Phys. B, 2022, 31 (3): 038101. DOI: 10.1088/1674-1056/ac1e11

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In order to significantly improve the absorption efficiency of monolayer molybdenum disulfide (M-MoS₂), an ultra-narrowband M-MoS₂ metamaterial absorber was obtained through theoretical analysis and numerical calculation using the finite difference time domain method. The physical mechanism can be better analyzed through critical coupling and guided mode resonance. Its absorption rate at λ = 806.41 nm is as high as 99.8%, which is more than 12 times that of bare M-MoS₂. From the simulation results, adjusting the geometric parameters of the structure can control the resonant wavelength range of the M-MoS₂. In addition, we also found that the maximum quality factor is 1256.8. The numerical result shows that the design provides new possibilities for ultra-narrowband M-MoS₂ perfect absorbers in the near-infrared spectrum. The results of this work indicate that the designed structure has excellent prospects for application in wavelength-selective photoluminescence and photodetection.

Differential nonlinear photocarrier radiometry for characterizing ultra-low energy boron implantation in silicon

Xiao-Ke Lei(雷晓轲), Bin-Cheng Li(李斌成), Qi-Ming Sun(孙启明), Jing Wang(王静), Chun-Ming Gao(高椿明), and Ya-Fei Wang(王亚非)

Chin. Phys. B, 2022, 31 (3): 038102. DOI: 10.1088/1674-1056/ac1efe

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The measuring of the depth profile and electrical activity of implantation impurity in the top nanometer range of silicon encounters various difficulties and limitations, though it is known to be critical in fabrication of silicon complementary metal-oxide-semiconductor (CMOS) devices. In the present work, SRIM program and photocarrier radiometry (PCR) are employed to monitor the boron implantation in industrial-grade silicon in an ultra-low implantation energy range from 0.5 keV to 5 keV. The differential PCR technique, which is improved by greatly shortening the measurement time through the simplification of reference sample, is used to investigate the effects of implantation energy on the frequency behavior of the PCR signal for ultra-shallow junction. The transport parameters and thickness of shallow junction, extracted via multi-parameter fitting the dependence of differential PCR signal on modulation frequency to the corresponding theoretical model, well explain the energy dependence of PCR signal and further quantitatively characterize the recovery degree of structure damage induced by ion implantation and the electrical activation degree of impurities. The monitoring of nm-level thickness and electronic properties exhibits high sensitivity and apparent monotonicity over the industrially relevant implantation energy range. The depth profiles of implantation boron in silicon with the typical electrical damage threshold (Y_ED) of 5.3×10¹⁵ cm^-3 are evaluated by the SRIM program, and the determined thickness values are consistent well with those extracted by the differential PCR. It is demonstrated that the SRIM and the PCR are both effective tools to characterize ultra-low energy ion implantation in silicon.

Characterization of the N-polar GaN film grown on C-plane sapphire and misoriented C-plane sapphire substrates by MOCVD Suggested by editors

Xiaotao Hu(胡小涛), Yimeng Song(宋祎萌), Zhaole Su(苏兆乐), Haiqiang Jia(贾海强), Wenxin Wang(王文新), Yang Jiang(江洋), Yangfeng Li(李阳锋), and Hong Chen(陈弘)

Chin. Phys. B, 2022, 31 (3): 038103. DOI: 10.1088/1674-1056/ac3bad

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Gallium nitride (GaN) thin film of the nitrogen polarity (N-polar) was grown on C-plane sapphire and misoriented C-plane sapphire substrates respectively by metal-organic chemical vapor deposition (MOCVD). The misorientation angle is off-axis from C-plane toward M-plane of the substrates, and the angle is 2° and 4° respectively. The nitrogen polarity was confirmed by examining the images of the scanning electron microscope before and after the wet etching in potassium hydroxide (KOH) solution. The morphology was studied by the optical microscope and atomic force microscope. The crystalline quality was characterized by the x-ray diffraction. The lateral coherence length, the tilt angle, the vertical coherence length, and the vertical lattice-strain were acquired using the pseudo-Voigt function to fit the x-ray diffraction curves and then calculating with four empirical formulae. The lateral coherence length increases with the misorientation angle, because higher step density and shorter distance between adjacent steps can lead to larger lateral coherence length. The tilt angle increases with the misorientation angle, which means that the misoriented substrate can degrade the identity of crystal orientation of the N-polar GaN film. The vertical lattice-strain decreases with the misorientation angle. The vertical coherence length does not change a lot as the misorientation angle increases and this value of all samples is close to the nominal thickness of the N-polar GaN layer. This study helps to understand the influence of the misorientation angle of misoriented C-plane sapphire on the morphology, the crystalline quality, and the microstructure of N-polar GaN films.

Influence of intramolecular hydrogen bond formation sites on fluorescence mechanism

Hong-Bin Zhan(战鸿彬), Heng-Wei Zhang(张恒炜), Jun-Jie Jiang(江俊杰), Yi Wang(王一), Xu Fei(费旭), and Jing Tian(田晶)

Chin. Phys. B, 2022, 31 (3): 038201. DOI: 10.1088/1674-1056/ac29ad

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The fluorescence mechanism of HBT-HBZ is investigated in this work. A fluorescent probe is used to detect HClO content in living cells and tap water, and its structure after oxidation by HClO (HBT-ClO) is discussed based on the density functional theory (DFT) and time-dependent density functional theory (TDDFT). At the same time, the influence of the probe conformation and the proton transfer site within the excited state molecule on the fluorescence mechanism are revealed. Combined with infrared vibrational spectra and atoms-in-molecules theory, the strength of intramolecular hydrogen bonds in HBT-HBZ and HBT-ClO and their isomers are demonstrated qualitatively. The relationship between the strength of intramolecular hydrogen bonds and dipole moments is discussed. The potential energy curves demonstrate the feasibility of intramolecular proton transfer. The weak fluorescence phenomenon of HBT-HBZ in solution is quantitatively explained by analyzing the frontier molecular orbital and hole electron caused by charge separation. Moreover, when strong cyan fluorescence occurs in solution, the corresponding molecular structure should be HBT-ClO(T). The influence of the intramolecular hydrogen bond formation site on the molecule as a whole is also investigated by electrostatic potential analysis.

A DFT/TD-DFT study of effect of different substituent on ESIPT fluorescence features of 2-(2'-hydroxyphenyl)-4-chloro- methylthiazole derivatives

Shen-Yang Su(苏申阳), Xiu-Ning Liang(梁秀宁), and Hua Fang(方华)

Chin. Phys. B, 2022, 31 (3): 038202. DOI: 10.1088/1674-1056/ac21c6

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Based on density functional theory (DFT) and time-dependent density functional theory (TD-DFT), the effects of substituent on the excited-state intramolecular proton transfer (ESIPT) process and photophysical properties of 2-(2'-hydroxyphenyl)-4-chloromethylthiazole (HCT) are studied. The electron-donating group (CH₃, OH) and electron-withdrawing group (CF₃, CHO) are introduced to analyze the changes of intramolecular H-bond, the frontier molecular orbitals, the absorption/fluorescence spectra, and the energy barrier of ESIPT process. The calculation results indicate that electron-donating group strengthens the intramolecular H-bond in the S₁ state, and leads to an easier ESIPT process. The electron-withdrawing group weakens the corresponding H-bond and makes ESIPT process a little harder. Different substituents also affect the photophysical properties of HCT. The electron-withdrawing group (CF₃, CHO) has a little effect on electronic spectra. The electron-donating group (CH₃, OH) red-shifts both the absorption and fluorescence emission peaks of HCT, respectively, which causes the Stokes shift to increase.

Lithium ion batteries cathode material: V₂O₅

Baohe Yuan(袁保合), Xiang Yuan(袁祥), Binger Zhang(张冰儿), Zheng An(安政), Shijun Luo(罗世钧), and Lulu Chen(陈露露)

Chin. Phys. B, 2022, 31 (3): 038203. DOI: 10.1088/1674-1056/ac21be

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Among all the known electrode materials, vanadium pentoxide (V₂O₅) has high reversible capacity. It is a very valuable material for research of the complexity, rich structure and morphology. However, it also has some disadvantages, such as poor cycle stability, low discharge voltage, low conductivity and Li⁺ diffusion coefficient. In this regard, researchers have carried out a lot of research, such as using various methods to improve the nanostructures, introducing heterostructures, introducing point defects or cation doping in the crystal structure, etc. The electrochemical performance of V₂O₅ has been significantly improved in reversible capacity, high-rate capacity and long-term cycle stability. In this paper, V₂O₅ based nanostructure with different chemical composition are briefly introduced, and it covers V₂O₅ nanomaterials with different morphology, including 1D nanorods, nanobelts, nanotubes, 2D leaf like nanosheets and other nanosheets, and 3D hollow structures, porous nanostructures, porous eggshell microsphere structures. The composite nanomaterials of V₂O₅ and different carbonaceous supports are also introduced. Finally, the V₂O₅ composite materials doped with cations are discussed. The electrochemical performance of V₂O₅ based electrode can be improved effectively by obtaining appropriate nanostructure and optimized chemical composition.

Measurements of the ¹⁰⁷Ag neutron capture cross sections with pulse height weighting technique at the CSNS Back-n facility

Xin-Xiang Li(李鑫祥), Long-Xiang Liu(刘龙祥), Wei Jiang(蒋伟), Jie Ren(任杰), Hong-Wei Wang(王宏伟), Gong-Tao Fan(范功涛), Jian-Jun He(何建军), Xi-Guang Cao(曹喜光), Long-Long Song(宋龙龙),Yue Zhang(张岳), Xin-Rong Hu(胡新荣), Zi-Rui Hao(郝子锐), Pan Kuang(匡攀), Bing Jiang(姜炳),Xiao-He Wang(王小鹤), Ji-Feng Hu(胡继峰), Jin-Cheng Wang(王金成), De-Xin Wang(王德鑫),Su-Yalatu Zhang(张苏雅拉吐), Ying-Du Liu(刘应都), Xu Ma(麻旭), Chun-Wang Ma(马春旺),Yu-Ting Wang(王玉廷), Zhen-Dong An(安振东), Jun Su(苏俊), Li-Yong Zhang(张立勇),Yu-Xuan Yang(杨宇萱), Wen-Bo Liu(刘文博), Wan-Qing Su(苏琬晴),Sheng Jin(金晟), and Kai-Jie Chen(陈开杰)

Chin. Phys. B, 2022, 31 (3): 038204. DOI: 10.1088/1674-1056/ac48fd

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Silver indium cadmium (Ag-In-Cd) control rod is widely used in pressurized water reactor nuclear power plants, and it is continuously consumed in a high neutron flux environment. The mass ratio of ¹⁰⁷Ag in the Ag-In-Cd control rod is 41.44%. To accurately calculate the consumption value of the control rod, a reliable neutron reaction cross section of the ¹⁰⁷Ag is required. Meanwhile, ¹⁰⁷Ag is also an important weak r nucleus. Thus, the cross sections for neutron induced interactions with ¹⁰⁷Ag are very important both in nuclear energy and nuclear astrophysics. The (n,γ) cross section of ¹⁰⁷Ag has been measured in the energy range of 1-60 eV using a back streaming white neutron beam line at China spallation neutron source. The resonance parameters are extracted by an R-matrix code. All the cross section of ¹⁰⁷Ag and resonance parameters are given in this paper as datasets. The datasets are openly available at http://www.doi.org/10.11922/sciencedb.j00113.00010.

A low-cost invasive microwave ablation antenna with a directional heating pattern

Zhang Wen(文章), Xian-Qi Lin(林先其), Chen-Nan Li(李晨楠), and Yu-Lu Fan(樊钰璐)

Chin. Phys. B, 2022, 31 (3): 038401. DOI: 10.1088/1674-1056/ac1e1b

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Microwave ablation (MWA) is a cancer treatment method. The tumor tissue absorbs electromagnetic energy, which heats and kills it. A microwave ablation antenna plays a critical role in this process. Its radiation field must completely cover the tumor but not the healthy tissue. At present, the radiation pattern of most invasive ablation antennas is spherical. However, in the clinic, the shape of some tumors may be asymmetrical or the antenna cannot be inserted into the center of the tumor for some other reason. In order to solve these problems, a directional heating antenna for microwave ablation is proposed in this paper. The proposed antenna, operating at 2.45 GHz, consists of a monopole and a reflector. The feed is given by a substrate integrated coaxial line (SICL) and coplanar waveguide (CPW). The omnidirectional radiation field of the monopole is reflected by a reflector that is extended from the outer conductors of the SICL to form a directional radiation field. The impedance matching network is designed on SICL to match the antenna to 50 Ω . The antenna is fabricated using a mature printed circuit board (PCB). The reflection coefficient of the antenna in porcine liver tissue measured by a vector network analyzer shows good agreement with the simulations. Then, an ablation experiment in porcine liver is conducted with power of 10 W for 10 min, and the experimental results confirm the validity of the design.

Applications and functions of rare-earth ions in perovskite solar cells

Limin Cang(苍利民), Zongyao Qian(钱宗耀), Jinpei Wang(王金培), Libao Chen(陈利豹), Zhigang Wan(万志刚), Ke Yang(杨柯), Hui Zhang(张辉), and Yonghua Chen(陈永华)

Chin. Phys. B, 2022, 31 (3): 038402. DOI: 10.1088/1674-1056/ac373a

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The emerging perovskite solar cells have been recognized as one of the most promising new-generation photovoltaic technologies owing to their potential of high efficiency and low production cost. However, the current perovskite solar cells suffer from some obstacles such as non-radiative charge recombination, mismatched absorption, light induced degradation for the further improvement of the power conversion efficiency and operational stability towards practical application. The rare-earth elements have been recently employed to effectively overcome these drawbacks according to their unique photophysical properties. Herein, the recent progress of the application of rare-earth ions and their functions in perovskite solar cells were systematically reviewed. As it was revealed that the rare-earth ions can be coupled with both charge transport metal oxides and photosensitive perovskites to regulate the thin film formation, and the rare-earth ions are embedded either substitutionally into the crystal lattices to adjust the optoelectronic properties and phase structure, or interstitially at grain boundaries and surface for effective defect passivation. In addition, the reversible oxidation and reduction potential of rare-earth ions can prevent the reduction and oxidation of the targeted materials. Moreover, owing to the presence of numerous energetic transition orbits, the rare-earth elements can convert low-energy infrared photons or high-energy ultraviolet photons into perovskite responsive visible light, to extend spectral response range and avoid high-energy light damage. Therefore, the incorporation of rare-earth elements into the perovskite solar cells have demonstrated promising potentials to simultaneously boost the device efficiency and stability.

Graphene-based heterojunction for enhanced photodetectors

Haiting Yao(姚海婷), Xin Guo(郭鑫), Aida Bao(鲍爱达), Haiyang Mao(毛海央),Youchun Ma(马游春), and Xuechao Li(李学超)

Chin. Phys. B, 2022, 31 (3): 038501. DOI: 10.1088/1674-1056/ac1b8b

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Graphene has high light transmittance of 97.7% and ultrafast carrier mobility, which means it has attracted widespread attention in two-dimensional materials. However, the optical absorptivity of single-layer graphene is only 2.3%, and the corresponding photoresponsivity is difficult to produce at normal light irradiation. And the low on—off ratio resulting from the zero bandgap makes it unsuitable for many electronic devices, hindering potential development. The graphene-based heterojunction composed of graphene and other materials has outstanding optical and electrical properties, which can mutually modify the defects of both the graphene and material making it then suitable for optoelectronic devices. In this review, the advantages of graphene-based heterojunctions in the enhancement of the performance of photodetectors are reviewed. Firstly, we focus on the photocurrent generation mechanism of a graphene-based heterojunction photodetector, especially photovoltaic, photoconduction and photogating effects. Secondly, the classification of graphene-based heterojunctions in different directions is summarized. Meanwhile, the latest research progress of graphene-transition metal dichalcogenide (TMD) heterojunction photodetectors with excellent performance in graphene-based heterostructures is introduced. Finally, the difficulties faced by the existing technologies of graphene-based photodetectors are discussed, and further prospects are proposed.

Magnetoresistance effect in vertical NiFe/graphene/NiFe junctions

Pei-Sen Li(李裴森), Jun-Ping Peng(彭俊平), Yue-Guo Hu(胡悦国), Yan-Rui Guo(郭颜瑞), Wei-Cheng Qiu(邱伟成), Rui-Nan Wu(吴瑞楠), Meng-Chun Pan(潘孟春), Jia-Fei Hu(胡佳飞), Di-Xiang Chen(陈棣湘), and Qi Zhang(张琦)

Chin. Phys. B, 2022, 31 (3): 038502. DOI: 10.1088/1674-1056/ac192e

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For convenient and efficient verification of the magnetoresistance effect in graphene spintronic devices, vertical magnetic junctions with monolayer graphene sandwiched between two NiFe electrodes are fabricated by a relatively simple way of transferring CVD graphene onto the bottom ferromagnetic stripes. The anisotropic magnetoresistance contribution is excluded by the experimental result of magnetoresistance (MR) ratio dependence on the magnetic field direction. The spin-dependent transport measurement reveals two distinct resistance states switching under an in-plane sweeping magnetic field. A magnetoresistance ratio of about 0.17 % is obtained at room temperature and it shows a typical monotonic downward trend with the bias current increasing. This bias dependence of MR further verifies that the spin transport signal in our device is not from the anisotropic magnetoresistance. Meanwhile, the I—V curve is found to manifest a linear behavior, which demonstrates the Ohmic contacts at the interface and the metallic transport characteristic of vertical graphene junction.

Analysis of the generation mechanism of the S-shaped J—V curves of MoS₂/Si-based solar cells Suggested by editors

He-Ju Xu(许贺菊), Li-Tao Xin(辛利桃), Dong-Qiang Chen(陈东强), Ri-Dong Cong(丛日东), and Wei Yu(于威)

Chin. Phys. B, 2022, 31 (3): 038503. DOI: 10.1088/1674-1056/ac1b80

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Amorphous-microcrystalline MoS$_{2}$ thin films are fabricated using the sol-gel method to produce MoS$_{2}$/Si-based solar cells. The generation mechanisms of the S-shaped current density-voltage ($J$-$V$) curves of the solar cells are analyzed. To improve the performance of the solar cells and address the problem of the S-shaped $J$-$V$ curve, a MoS$_{2}$ film and a p$^+$ layer are introduced into the front and back interfaces of the solar cell, respectively, which leads to the formation of a p-n junction between the p-Si and the MoS$_{2}$ film as well as ohmic contacts between the MoS$_{2}$ film and the ITO, improving the S-shaped $J$-$V$ curve. As a result of the high doping characteristics and the high work function of the p$^+$ layer, a high-low junction is formed between the p$^+$ and p layers along with ohmic contacts between the p$^+$ layer and the Ag electrode. Consequently, the S-shaped $J$-$V$ curve is eliminated, and a significantly higher current density is achieved at a high voltage. The device exhibits ideal p-n junction rectification characteristics and achieves a high power-conversion efficiency (CE) of 7.55%. The findings of this study may improve the application of MoS$_{2}$ thin films in silicon-based solar cells, which are expected to be widely used in various silicon-based electronic and optical devices.

Facile sensitizing of PbSe film for near-infrared photodetector by microwave plasma processing

Kangyi Zhao(赵康伊), Shuanglong Feng(冯双龙), Chan Yang(杨婵),Jun Shen(申钧), and Yongqi Fu(付永启)

Chin. Phys. B, 2022, 31 (3): 038504. DOI: 10.1088/1674-1056/ac3224

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High quality PbSe film was first fabricated by a thermal evaporation method, and then the effect of plasma sensitization on the PbSe film was systemically investigated. Typical detectivity and significant photosensitivity are achieved in the PbSe-based photodetector, reaching maximum values of 7.6×10⁹ cm·Hz^1/2/W and 1.723 A/W, respectively. Compared with thermal annealing, plasma sensitization makes the sensitization easier and significantly improves the performance.

Long range electromagnetic field nature of nerve signal propagation in myelinated axons

Qing-Wei Zhai(翟卿伟), Kelvin J A Ooi(黄健安), Sheng-Yong Xu(许胜勇), and C K Ong(翁宗经)

Chin. Phys. B, 2022, 31 (3): 038701. DOI: 10.1088/1674-1056/ac1e1a

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The nature of saltatory conduction in myelinated axon described by equivalent circuit and circuit theory is still contentious. Recent experimental observations of action potentials transmitting through disjointed nerve fibers strongly suggest an electromagnetic wave propagation mechanism of the nerve signals. In this paper, we employ the electromagnetic wave model of the myelinated axon to describe action potential signal propagation. We use the experimental frequency-dependent conductivity and permittivity values of the nerve tissues in order to reliably calculate the electromagnetic modes by using electromagnetic mode solvers. We find that the electromagnetic waves above 10 {kHz} can be well confined in extracellular fluid—myelin sheath—intracellular fluid waveguide and propagate a distance of 7 mm without much attenuation. Our study may serve as one of the fundamental researches for the better understanding of the nervous system.

Charge transfer modification of inverted planar perovskite solar cells by NiO_x/Sr:NiO_x bilayer hole transport layer

Qiaopeng Cui(崔翘鹏), Liang Zhao(赵亮), Xuewen Sun(孙学文), Qiannan Yao(姚倩楠), Sheng Huang(黄胜), Lei Zhu(朱磊), Yulong Zhao(赵宇龙), Jian Song(宋健), and Yinghuai Qiang(强颖怀)

Chin. Phys. B, 2022, 31 (3): 038801. DOI: 10.1088/1674-1056/ac1fda

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Perovskite solar cells (PSCs) are the most promising commercial photoelectric conversion technology in the future. The planar p-i-n structure cells have advantages in negligible hysteresis, low temperature preparation and excellent stability. However, for inverted planar PSCs, the non-radiative recombination at the interface is an important reason that impedes the charge transfer and improvement of power conversion efficiency. Having a homogeneous, compact, and energy-level-matched charge transport layer is the key to reducing non-radiative recombination. In our study, NiO$_{x}$/Sr:NiO$_{x}$ bilayer hole transport layer (HTL) improves the holes transmission of NiO$_{x}$ based HTL, reduces the recombination in the interface between perovskite and HTL layer and improves the device performance. The bilayer HTL enhances the hole transfer by forming a driving force of an electric field and further improves $J_{\rm sc}$. As a result, the device has a power conversion efficiency of 18.44%, a short circuit current density of 22.81 mA$\cdot$cm$^{-2}$ and a fill factor of 0.80. Compared to the pristine PSCs, there are certain improvements of optical parameters. This method provides a new idea for the future design of novel hole transport layers and the development of high-performance solar cells.

Effect of net carriers at the interconnection layer in tandem organic solar cells Suggested by editors

Li-Jia Chen(陈丽佳), Guo-Xi Niu(牛国玺), Lian-Bin Niu(牛连斌), and Qun-Liang Song(宋群梁)

Chin. Phys. B, 2022, 31 (3): 038802. DOI: 10.1088/1674-1056/ac4485

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Tandem cell with structure of indium tin oxide (ITO)/molybdenum oxide (MoO₃)/fullerene (C60)/copper phthalocyanine (CuPc)/C60/tris-8-hydroxy-quinolinato aluminum (Alq₃)/Al was fabricated to study the effect of net carriers at the interconnection layer. The open circuit voltage and short circuit current were found to be 1.15 V and 0.56 mA/cm², respectively. Almost the same performance (1.05 V, 0.58 mA/cm²

An n—n type heterojunction enabling highly efficientcarrier separation in inorganic solar cells

Gang Li(李刚), Yuqian Huang(黄玉茜), Rongfeng Tang(唐荣风), Bo Che(车波), Peng Xiao(肖鹏), Weitao Lian(连伟涛), Changfei Zhu(朱长飞), and Tao Chen(陈涛)

Chin. Phys. B, 2022, 31 (3): 038803. DOI: 10.1088/1674-1056/ac4022

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Carrier separation in a solar cell usually relies on the p—n junction. Here we show that an n—n type inorganic semiconductor heterojunction is also able to separate the exciton for efficient solar cell applications. The n—n type heterojunction was formed by hydrothermal deposition of Sb₂(S,Se)₃ and thermal evaporation of Sb₂Se₃. We found that the n—n junction is able to enhance the carrier separation by the formation of an electric field, reduce the interfacial recombination and generate optimized band alignment. The device based on this n—n junction shows 2.89% net efficiency improvement to 7.75% when compared with the device consisted of semiconductor absorber—metal contact. The study in the n—n type solar cell is expected to bring about more versatile materials utility, new interfacial engineering strategy and fundamental findings in the photovoltaic energy conversion process.

Reveal the large open-circuit voltage deficit of all-inorganicCsPbIBr₂ perovskite solar cells

Ying Hu(胡颖), Jiaping Wang(王家平), Peng Zhao(赵鹏), Zhenhua Lin(林珍华), Siyu Zhang(张思玉), Jie Su(苏杰), Miao Zhang(张苗), Jincheng Zhang(张进成), Jingjing Chang(常晶晶), and Yue Hao(郝跃)

Chin. Phys. B, 2022, 31 (3): 038804. DOI: 10.1088/1674-1056/ac464b

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Due to excellent thermal stability and optoelectronic properties, all-inorganic perovskite is one of the promising candidates to solve the thermal decomposition problem of conventional organic—inorganic hybrid perovskite solar cells (PSCs), but the larger voltage loss (V_loss) cannot be ignored, especially CsPbIBr₂, which limits the improvement of efficiency. To reduce V_loss, one promising solution is the modification of the energy level alignment between the perovskite layer and adjacent charge transport layer (CTL), which can facilitate charge extraction and reduce carrier recombination rate at the perovskite/CTL interface. Therefore, the key issues of minimum V_loss and high efficiency of CsPbIBr₂-based PSCs were studied in terms of the perovskite layer thickness, the effects of band offset of the CTL/perovskite layer, the doping concentration of the CTL, and the electrode work function in this study based on device simulations. The open-circuit voltage (V_oc) is increased from 1.37 V to 1.52 V by replacing SnO₂ with ZnO as the electron transport layer (ETL) due to more matching conduction band with the CsPbIBr₂ layer.

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