Table of contents

18 January 2021, Volume 30 Issue 2 Previous issue    Next issue

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GENERAL

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Novel traveling wave solutions and stability analysis of perturbed Kaup-Newell Schrödinger dynamical model and its applications Xiaoyong Qian(钱骁勇), Dianchen Lu(卢殿臣), Muhammad Arshad, and Khurrem Shehzad Chin. Phys. B, 2021, 30 (2):  020201.  DOI: 10.1088/1674-1056/abbbfc Abstract ( 437 )   HTML ( 4 )   PDF (2880KB) ( 99 )   We study the traveling wave and other solutions of the perturbed Kaup-Newell Schrödinger dynamical equation that signifies long waves parallel to the magnetic field. The wave solutions such as bright-dark (solitons), solitary waves, periodic and other wave solutions of the perturbed Kaup-Newell Schrödinger equation in mathematical physics are achieved by utilizing two mathematical techniques, namely, the extended F-expansion technique and the proposed exp\((-\phi(\xi))\)-expansion technique. This dynamical model describes propagation of pluses in optical fibers and can be observed as a special case of the generalized higher order nonlinear Schrödinger equation. In engineering and applied physics, these wave results have key applications. Graphically, the structures of some solutions are presented by giving specific values to parameters. By using modulation instability analysis, the stability of the model is tested, which shows that the model is stable and the solutions are exact. These techniques can be fruitfully employed to further sculpt models that arise in mathematical physics.

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A local refinement purely meshless scheme for time fractional nonlinear Schrödinger equation in irregular geometry region Tao Jiang(蒋涛), Rong-Rong Jiang(蒋戎戎), Jin-Jing Huang(黄金晶), Jiu Ding(丁玖), and Jin-Lian Ren(任金莲) Chin. Phys. B, 2021, 30 (2):  020202.  DOI: 10.1088/1674-1056/abc0e0 Abstract ( 364 )   HTML ( 1 )   PDF (2345KB) ( 83 )   A local refinement hybrid scheme (LRCSPH-FDM) is proposed to solve the two-dimensional (2D) time fractional nonlinear Schrödinger equation (TF-NLSE) in regularly or irregularly shaped domains, and extends the scheme to predict the quantum mechanical properties governed by the time fractional Gross-Pitaevskii equation (TF-GPE) with the rotating Bose-Einstein condensate. It is the first application of the purely meshless method to the TF-NLSE to the author's knowledge. The proposed LRCSPH-FDM (which is based on a local refinement corrected SPH method combined with FDM) is derived by using the finite difference scheme (FDM) to discretize the Caputo TF term, followed by using a corrected smoothed particle hydrodynamics (CSPH) scheme continuously without using the kernel derivative to approximate the spatial derivatives. Meanwhile, the local refinement technique is adopted to reduce the numerical error. In numerical simulations, the complex irregular geometry is considered to show the flexibility of the purely meshless particle method and its advantages over the grid-based method. The numerical convergence rate and merits of the proposed LRCSPH-FDM are illustrated by solving several 1D/2D (where 1D stands for one-dimensional) analytical TF-NLSEs in a rectangular region (with regular or irregular particle distribution) or in a region with irregular geometry. The proposed method is then used to predict the complex nonlinear dynamic characters of 2D TF-NLSE/TF-GPE in a complex irregular domain, and the results from the posed method are compared with those from the FDM. All the numerical results show that the present method has a good accuracy and flexible application capacity for the TF-NLSE/GPE in regions of a complex shape.

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Coherent-driving-assisted quantum speedup in Markovian channels Xiang Lu(鹿翔), Ying-Jie Zhang(张英杰), and Yun-Jie Xia(夏云杰) Chin. Phys. B, 2021, 30 (2):  020301.  DOI: 10.1088/1674-1056/abc150 Abstract ( 421 )   HTML ( 2 )   PDF (4093KB) ( 91 )   As is well known, the quantum evolution speed of quantum state can never be accelerated in the Markovian regime without any operators on the system. The Hamiltonian corrections induced by the action of coherent driving forces are often used to fight dissipative and decoherence mechanisms in experiments. For this reason, considering three noisy channels (the phase-flip channel, the amplitude damping channel and the depolarizing channel), we propose a scheme of speedup evolution of an open system by controlling an external unitary coherent driving operator on the system. It is shown that, in the presence of the coherent driving, no-speedup evolution can be transformed into quantum speedup evolution in the Markovian dynamics process. Additionally, under the fixed coherent driving strength in the above three noisy channels, the best way to achieve the most degree of quantum speedup for the system has been acquired by rotating the system with appropriate driving direction angles, respectively. Finally, we conclude that the reason for this acceleration is not the non-Markovian dynamical behavior of the system but due to the oscillation of geometric distance between the initial state and the target final state.

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Quantifying entanglement in terms of an operational way Deng-Hui Yu(于登辉) and Chang-Shui Yu(于长水) Chin. Phys. B, 2021, 30 (2):  020302.  DOI: 10.1088/1674-1056/abc157 Abstract ( 529 )   HTML ( 4 )   PDF (442KB) ( 145 )   We establish entanglement monotones in terms of an operational approach, which is closely connected with the state conversion from pure states to the objective state by the local operations and classical communications. It is shown that any good entanglement quantifier defined on pure states can induce an entanglement monotone for all density matrices. Particularly, we show that our entanglement monotone is the maximal one among all those having the same form for pure states. In some special cases, our proposed entanglement monotones turn to be equivalent to the convex roof construction, which hence gain an operational meaning. Some examples are given to demonstrate different cases.

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Tunable ponderomotive squeezing in an optomechanical system with two coupled resonators Qin Wu(吴琴) Chin. Phys. B, 2021, 30 (2):  020303.  DOI: 10.1088/1674-1056/abb7f5 Abstract ( 444 )   HTML ( 3 )   PDF (578KB) ( 135 )   We investigate properties of the ponderomotive squeezing in an optomechanical system with two coupled resonators, where the tunable two-mode squeezing spectrum can be observed from the output field. It is realized that the squeezing orientation can be controlled by the detuning between the left cavity and pump laser. Especially, both cavity decay and environment temperature play a positive role in generating better pondermotive squeezing light. Strong squeezing spectra with a wide squeezing frequency range can be obtained by appropriate choice of parameters present in our optomechanical system.

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State transfer on two-fold Cayley trees via quantum walks Xi-Ling Xue(薛希玲) and Yue Ruan(阮越) Chin. Phys. B, 2021, 30 (2):  020304.  DOI: 10.1088/1674-1056/abcfa1 Abstract ( 388 )   HTML ( 2 )   PDF (724KB) ( 185 )   Perfect state transfer (PST) has great significance due to its applications in quantum information processing and quantum computation. The main problem we study in this paper is to determine whether the two-fold Cayley tree, an extension of the Cayley tree, admits perfect state transfer between two roots using quantum walks. We show that PST can be achieved by means of the so-called nonrepeating quantum walk [Phys. Rev. A 89 042332 (2014)] within time steps that are the distance between the two roots; while both the continuous-time quantum walk and the typical discrete-time quantum walk with Grover coin approaches fail. Our results suggest that in some cases the dynamics of a discrete-time quantum walk may be much richer than that of the continuous-time quantum walk.

TOPICAL REVIEW—Quantum computation and quantum simulation

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A concise review of Rydberg atom based quantum computation and quantum simulation Xiaoling Wu(吴晓凌), Xinhui Liang(梁昕晖), Yaoqi Tian(田曜齐), Fan Yang(杨帆), Cheng Chen(陈丞), Yong-Chun Liu(刘永椿), Meng Khoon Tey(郑盟锟), and Li You(尤力) Chin. Phys. B, 2021, 30 (2):  020305.  DOI: 10.1088/1674-1056/abd76f Abstract ( 2197 )   HTML ( 51 )   PDF (3178KB) ( 1697 )   Quantum information processing based on Rydberg atoms emerged as a promising direction two decades ago. Recent experimental and theoretical progresses have shined exciting light on this avenue. In this concise review, we will briefly introduce the basics of Rydberg atoms and their recent applications in associated areas of neutral atom quantum computation and simulation. We shall also include related discussions on quantum optics with Rydberg atomic ensembles, which are increasingly used to explore quantum computation and quantum simulation with photons.

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Selected topics of quantum computing for nuclear physics Dan-Bo Zhang(张旦波), Hongxi Xing(邢宏喜), Hui Yan(颜辉), Enke Wang(王恩科), and Shi-Liang Zhu(朱诗亮) Chin. Phys. B, 2021, 30 (2):  020306.  DOI: 10.1088/1674-1056/abd761 Abstract ( 622 )   HTML ( 7 )   PDF (915KB) ( 471 )   Nuclear physics, whose underling theory is described by quantum gauge field coupled with matter, is fundamentally important and yet is formidably challenge for simulation with classical computers. Quantum computing provides a perhaps transformative approach for studying and understanding nuclear physics. With rapid scaling-up of quantum processors as well as advances on quantum algorithms, the digital quantum simulation approach for simulating quantum gauge fields and nuclear physics has gained lots of attention. In this review, we aim to summarize recent efforts on solving nuclear physics with quantum computers. We first discuss a formulation of nuclear physics in the language of quantum computing. In particular, we review how quantum gauge fields (both Abelian and non-Abelian) and their coupling to matter field can be mapped and studied on a quantum computer. We then introduce related quantum algorithms for solving static properties and real-time evolution for quantum systems, and show their applications for a broad range of problems in nuclear physics, including simulation of lattice gauge field, solving nucleon and nuclear structures, quantum advantage for simulating scattering in quantum field theory, non-equilibrium dynamics, and so on. Finally, a short outlook on future work is given.

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Review of quantum simulation based on Rydberg many-body system Zheng-Yuan Zhang(张正源), Dong-Sheng Ding(丁冬生), and Bao-Sen Shi(史保森) Chin. Phys. B, 2021, 30 (2):  020307.  DOI: 10.1088/1674-1056/abd744 Abstract ( 668 )   HTML ( 8 )   PDF (3357KB) ( 509 )   Quantum simulation has been developed extensively over the past decades, widely applied to different models to explore dynamics in the quantum regime. Rydberg atoms have strong dipole-dipole interactions and interact with each other over a long distance, which makes it straightforward to build many-body interacting quantum systems to simulate specific models. Additionally, neutral atoms are easily manipulated due to their weak interactions. These advantages make Rydberg many-body system an ideal platform to implement quantum simulations. This paper reviews several quantum simulations for different models based on Rydberg many-body systems, including quantum Ising models in one dimension and two dimensions mainly for quantum magnetism, XY model for excitation transport, SSH model for symmetry-protected topological phases, and critical self-organized behaviors in many-body systems. Besides, some challenges and promising directions of quantum simulations based on Rydberg many-body system are discussed in this paper.

SPECIAL TOPIC—Quantum computation and quantum simulation

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Quantum algorithm for a set of quantum 2SAT problems Yanglin Hu(胡杨林), Zhelun Zhang(张哲伦), and Biao Wu(吴飙) Chin. Phys. B, 2021, 30 (2):  020308.  DOI: 10.1088/1674-1056/abd741 Abstract ( 862 )   HTML ( 7 )   PDF (543KB) ( 231 )   We present a quantum adiabatic algorithm for a set of quantum 2-satisfiability (Q2SAT) problem, which is a generalization of 2-satisfiability (2SAT) problem. For a Q2SAT problem, we construct the Hamiltonian which is similar to that of a Heisenberg chain. All the solutions of the given Q2SAT problem span the subspace of the degenerate ground states. The Hamiltonian is adiabatically evolved so that the system stays in the degenerate subspace. Our numerical results suggest that the time complexity of our algorithm is O(n3.9) for yielding non-trivial solutions for problems with the number of clauses m=dn(n-1)/2 (\(d\lesssim 0.1\)). We discuss the advantages of our algorithm over the known quantum and classical algorithms.

GENERAL

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Analysis and implementation of new fractional-order multi-scroll hidden attractors Li Cui(崔力), Wen-Hui Luo(雒文辉), and Qing-Li Ou(欧青立) Chin. Phys. B, 2021, 30 (2):  020501.  DOI: 10.1088/1674-1056/abbbe4 Abstract ( 463 )   HTML ( 4 )   PDF (2818KB) ( 182 )   To improve the complexity of chaotic signals, in this paper we first put forward a new three-dimensional quadratic fractional-order multi-scroll hidden chaotic system, then we use the Adomian decomposition algorithm to solve the proposed fractional-order chaotic system and obtain the chaotic phase diagrams of different orders, as well as the Lyaponov exponent spectrum, bifurcation diagram, and SE complexity of the 0.99-order system. In the process of analyzing the system, we find that the system possesses the dynamic behaviors of hidden attractors and hidden bifurcations. Next, we also propose a method of using the Lyapunov exponents to describe the basins of attraction of the chaotic system in the matlab environment for the first time, and obtain the basins of attraction under different order conditions. Finally, we construct an analog circuit system of the fractional-order chaotic system by using an equivalent circuit module of the fractional-order integral operators, thus realizing the 0.9-order multi-scroll hidden chaotic attractors.

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Investigation of bright and dark solitons in α, β-Fermi Pasta Ulam lattice Nkeh Oma Nfor, Serge Bruno Yamgou, and Francois Marie Moukam Kakmeni Chin. Phys. B, 2021, 30 (2):  020502.  DOI: 10.1088/1674-1056/abbbf3 Abstract ( 392 )   HTML ( 1 )   PDF (2262KB) ( 63 )   We consider the Hamiltonian of α, β-Fermi Pasta Ulam lattice and explore the Hamilton-Jacobi formalism to obtain the discrete equation of motion. By using the continuum limit approximations and incorporating some normalized parameters, the extended Korteweg-de Vries equation is obtained, with solutions that elucidate on the Fermi Pasta Ulam paradox. We further derive the nonlinear Schrödinger amplitude equation from the extended Korteweg-de Vries equation, by exploring the reductive perturbative technique. The dispersion and nonlinear coefficients of this amplitude equation are functions of the α and β parameters, with the β parameter playing a crucial role in the modulational instability analysis of the system. For β greater than or equal to zero, no modulational instability is observed and only dark solitons are identified in the lattice. However for β less than zero, bright solitons are traced in the lattice for some large values of the wavenumber. Results of numerical simulations of both the Korteweg-de Vries and nonlinear Schrödinger amplitude equations with periodic boundary conditions clearly show that the bright solitons conserve their amplitude and shape after collisions.

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Breather solutions of modified Benjamin-Bona-Mahony equation G T Adamashvili Chin. Phys. B, 2021, 30 (2):  020503.  DOI: 10.1088/1674-1056/abc0d9 Abstract ( 339 )   PDF (912KB) ( 120 )   New two-component vector breather solution of the modified Benjamin-Bona-Mahony (MBBM) equation is considered. Using the generalized perturbation reduction method, the MBBM equation is reduced to the coupled nonlinear Schrödinger equations for auxiliary functions. Explicit analytical expressions for the profile and parameters of the vector breather oscillating with the sum and difference of the frequencies and wavenumbers are presented. The two-component vector breather and single-component scalar breather of the MBBM equation is compared.

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Dynamic phase transition of ferroelectric nanotube described by a spin-1/2 transverse Ising model Chundong Wang(王春栋), Ying Wu(吴瑛), Yulin Cao(曹喻霖), and Xinying Xue(薛新英) Chin. Phys. B, 2021, 30 (2):  020504.  DOI: 10.1088/1674-1056/abbbfd Abstract ( 477 )   HTML ( 2 )   PDF (1755KB) ( 204 )   The dynamic phase transition properties for ferroelectric nanotube under a spin-1/2 transverse Ising model are studied under the effective field theory (EFT) with correlations. The temperature effects on the pseudo-spin systems are unveiled in three-dimensional (3-D) and two-dimensional (2-D) phase diagrams. Moreover, the dynamic behaviors of exchange interactions on the 3-D and 2-D phase transitions under high temperature are exhibited. The results present that it is hard to obtain pure ferroelectric phase under high temperature; that is, the vibration of orderly pseudo-spins cannot be eliminated completely.

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A multi-directional controllable multi-scroll conservative chaos generator: Modelling, analysis, and FPGA implementation En-Zeng Dong(董恩增), Rong-Hao Li(李荣昊), and Sheng-Zhi Du(杜升之) Chin. Phys. B, 2021, 30 (2):  020505.  DOI: 10.1088/1674-1056/abc239 Abstract ( 368 )   HTML ( 5 )   PDF (3526KB) ( 104 )   Combing with the generalized Hamiltonian system theory, by introducing a special form of sinusoidal function, a class of n-dimensional (n = 1,2,3) controllable multi-scroll conservative chaos with complicated dynamics is constructed. The dynamics characteristics including bifurcation behavior and coexistence of the system are analyzed in detail, the latter reveals abundant coexisting flows. Furthermore, the proposed system passes the NIST tests and has been implemented physically by FPGA. Compared to the multi-scroll dissipative chaos, the experimental portraits of the proposed system show better ergodicity, which have potential application value in secure communication and image encryption.

SPECIAL TOPIC—Quantum computation and quantum simulation

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Quantum dynamics on a lossy non-Hermitian lattice Li Wang(王利), Qing Liu(刘青), and Yunbo Zhang(张云波) Chin. Phys. B, 2021, 30 (2):  020506.  DOI: 10.1088/1674-1056/abd765 Abstract ( 582 )   HTML ( 4 )   PDF (3294KB) ( 354 )   We investigate quantum dynamics of a quantum walker on a finite bipartite non-Hermitian lattice, in which the particle can leak out with certain rate whenever it visits one of the two sublattices. Quantum walker initially located on one of the non-leaky sites will finally totally disappear after a length of evolution time and the distribution of decay probability on each unit cell is obtained. In one regime, the resultant distribution shows an expected decreasing behavior as the distance from the initial site increases. However, in the other regime, we find that the resultant distribution of local decay probability is very counterintuitive, in which a relatively high population of decay probability appears on the edge unit cell which is the farthest from the starting point of the quantum walker. We then analyze the energy spectrum of the non-Hermitian lattice with pure loss, and find that the intriguing behavior of the resultant decay probability distribution is intimately related to the existence and specific property of the edge states, which are topologically protected and can be well predicted by the non-Bloch winding number. The exotic dynamics may be observed experimentally with arrays of coupled resonator optical waveguides.

GENERAL

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Design and FPGA implementation of multi-wing chaotic switched systems based on a quadratic transformation Qing-Yu Shi(石擎宇), Xia Huang(黄霞), Fang Yuan(袁方), and Yu-Xia Li(李玉霞) Chin. Phys. B, 2021, 30 (2):  020507.  DOI: 10.1088/1674-1056/abd74c Abstract ( 501 )   HTML ( 2 )   PDF (10231KB) ( 171 )   Based on a quadratic transformation and a switching function, a novel multi-wing chaotic switched system is proposed. First, a 4-wing chaotic system is constructed from a 2-wing chaotic system on the basis of a quadratic transformation. Then, a switching function is designed and by adjusting the switching function, the number and the distribution of the saddle-focus equilibrium points of the switched system can be regulated. Thus, a set of chaotic switched systems, which can produce 6-to-8-12-16-wing attractors, are generated. The Lyapunov exponent spectra, bifurcation diagrams, and Poincar\'e maps are given to verify the existence of the chaotic attractors. Besides, the digital circuit of the multi-wing chaotic switched system is designed by using the Verilog HDL fixed-point algorithm and the state machine control. Finally, the multi-wing chaotic attractors are demonstrated via FPGA platform. The experimental results show that the number of the wings of the chaotic attractors can be expanded more effectively with the combination of the quadratic transformation and the switching function methods.

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In-situ fabrication of ZnO nanoparticles sensors based on gas-sensing electrode for ppb-level H2S detection at room temperature Jing-Yue Xuan(宣景悦), Guo-Dong Zhao(赵国栋), Xiao-Bo Shi(史小波), Wei Geng(耿伟), Heng-Zheng Li(李恒征), Mei-Ling Sun(孙美玲), Fu-Chao Jia(贾福超), Shu-Gang Tan(谭树刚), Guang-Chao Yin(尹广超), and Bo Liu(刘波) Chin. Phys. B, 2021, 30 (2):  020701.  DOI: 10.1088/1674-1056/abcf46 Abstract ( 496 )   HTML ( 2 )   PDF (4502KB) ( 216 )   The zinc oxide (ZnO) nanoparticles (NPs) sensors were prepared in-situ on the gas-sensing electrodes by a one-step simple sol-gel method for the detection of hydrogen sulfide (H2S) gas. The sphere-like ZnO NPs were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), x-ray diffraction (XRD), energy dispersive x-ray analysis (EDX), and their H2S sensing performance were measured at room temperature. Testing results indicate that the ZnO NPs exhibit excellent response to H2S gas at room temperature. The response value of the optimal sample to 750 ppb H2S is 73.3%, the detection limit reaches to 30 ppb, and the response value is 7.5%. Furthermore, the effects of the calcining time and thickness of the film on the gas-sensing performance were investigated. Both calcining time and film thickness show a negative correlation with the H2S sensing performance. The corresponding reaction mechanism of H2S detection was also discussed.

TOPICAL REVIEW—Quantum computation and quantum simulation

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Low-temperature environments for quantum computation and quantum simulation Hailong Fu(付海龙), Pengjie Wang(王鹏捷), Zhenhai Hu(胡禛海), Yifan Li(李亦璠), and Xi Lin(林熙) Chin. Phys. B, 2021, 30 (2):  020702.  DOI: 10.1088/1674-1056/abd762 Abstract ( 888 )   HTML ( 18 )   PDF (957KB) ( 561 )   This review summarizes the requirement of low temperature conditions in existing experimental approaches to quantum computation and quantum simulation.

ATOMIC AND MOLECULAR PHYSICS

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Complex coordinate rotation method based on gradient optimization Hot! Zhi-Da Bai(白志达), Zhen-Xiang Zhong(钟振祥), Zong-Chao Yan(严宗朝), and Ting-Yun Shi(史庭云) Chin. Phys. B, 2021, 30 (2):  023101.  DOI: 10.1088/1674-1056/abc156 Abstract ( 632 )   HTML ( 4 )   PDF (586KB) ( 325 )   In atomic, molecular, and nuclear physics, the method of complex coordinate rotation is a widely used theoretical tool for studying resonant states. Here, we propose a novel implementation of this method based on the gradient optimization (CCR-GO). The main strength of the CCR-GO method is that it does not require manual adjustment of optimization parameters in the wave function; instead, a mathematically well-defined optimization path can be followed. Our method is proven to be very efficient in searching resonant positions and widths over a variety of few-body atomic systems, and can significantly improve the accuracy of the results. As a special case, the CCR-GO method is equally capable of dealing with bound-state problems with high accuracy, which is traditionally achieved through the usual extreme conditions of energy itself.

SPECIAL TOPIC—Quantum computation and quantum simulation

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Dissipative preparation of multipartite Greenberger-Horne-Zeilinger states of Rydberg atoms Chong Yang(杨崇), Dong-Xiao Li(李冬啸), and Xiao-Qiang Shao(邵晓强) Chin. Phys. B, 2021, 30 (2):  023201.  DOI: 10.1088/1674-1056/abd755 Abstract ( 419 )   HTML ( 2 )   PDF (782KB) ( 368 )   The multipartite Greenberger-Horne-Zeilinger (GHZ) states play an important role in large-scale quantum information processing. We utilize the polychromatic driving fields and the engineered spontaneous emissions of Rydberg states to dissipatively drive three-and four-partite neutral atom systems into the steady GHZ states, at the presence of the next-nearest neighbor interaction of excited Rydberg states. Furthermore, the introduction of quantum Lyapunov control can help us optimize the dissipative dynamics of the system so as to shorten the convergence time of the target state, improve the robustness against the spontaneous radiations of the excited Rydberg states, and release the limiting condition for the strengths of the polychromatic driving fields. Under the feasible experimental conditions, the fidelities of three-and four-partite GHZ states can be stabilized at 99.24% and 98.76%, respectively.

ATOMIC AND MOLECULAR PHYSICS

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Evidence of potential change in nonsequential double ionization Changchun Jia(贾昌春), Pu Zhang(张朴), Hua Wen(文华), and Zhangjin Chen(陈长进) Chin. Phys. B, 2021, 30 (2):  023401.  DOI: 10.1088/1674-1056/abc151 Abstract ( 419 )   HTML ( 1 )   PDF (1659KB) ( 53 )   Recently, the quantitative rescattering model (QRS) for nonsequential double ionization (NSDI) is modified by taking into account the potential change (PC) due to the presence of electric field at the time of recollision. Using the improved QRS model, we simulate the longitudinal momentum distributions of doubly charged ions He2+ by projecting the correlated two-electron momentum distributions for NSDI of He onto the main diagonal. The obtained results are compared directly with the experimental data at different intensities. It is found that when the PC is considered, the width of momentum distributions reduces and the agreement between theory and experiment is improved.

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Ground state cooling of an optomechanical resonator with double quantum interference processes Shuo Zhang(张硕), Tan Li(李坦), Qian-Hen Duan(段乾恒), Jian-Qi Zhang(张建奇), and Wan-Su Bao(鲍皖苏) Chin. Phys. B, 2021, 30 (2):  023701.  DOI: 10.1088/1674-1056/abc2c0 Abstract ( 420 )   HTML ( 7 )   PDF (1638KB) ( 194 )   We present a cooling scheme with a tripod configuration atomic ensemble trapped in an optomechanical cavity. With the employment of two different quantum interference processes, our scheme illustrates that it is possible to cool a resonator to its ground state in the strong cavity-atom coupling regime. Moreover, with the assistance of one additional energy level, our scheme takes a larger cooling rate to realize the ground state cooling. In addition, this scheme is a feasible candidate for experimental applications.

ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS

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A fast and precise three-dimensional measurement system based on multiple parallel line lasers Yao Wang(王尧) and Bin Lin(林斌) Chin. Phys. B, 2021, 30 (2):  024201.  DOI: 10.1088/1674-1056/abc14d Abstract ( 373 )   HTML ( 7 )   PDF (927KB) ( 139 )   This paper conducts a trade-off between efficiency and accuracy of three-dimensional (3D) shape measurement based on the triangulation principle, and introduces a flying and precise 3D shape measurement method based on multiple parallel line lasers. Firstly, we establish the measurement model of the multiple parallel line lasers system, and introduce the concept that multiple base planes can help to deduce the unified formula of the measurement system and are used in simplifying the process of the calibration. Then, the constraint of the line spatial frequency, which maximizes the measurement efficiency while ensuring accuracy, is determined according to the height distribution of the object. Secondly, the simulation analyzing the variation of the systemic resolution quantitatively under the circumstance of a set of specific parameters is performed, which provides a fundamental thesis for option of the four system parameters. Thirdly, for the application of the precision measurement in the industrial field, additional profiles are acquired to improve the lateral resolution by applying a motor to scan the 3D surface. Finally, compared with the line laser, the experimental study shows that the present method of obtaining 41220 points per frame improves the measurement efficiency. Furthermore, the accuracy and the process of the calibration are advanced in comparison with the existing multiple-line laser and the structured light makes an accuracy better than 0.22 mm at a distance of 956.02 mm.

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Propagation properties and radiation force of circular Airy Gaussian vortex beams in strongly nonlocal nonlinear medium Xinyu Liu(刘欣宇), Chao Sun(孙超), and Dongmei Deng(邓冬梅) Chin. Phys. B, 2021, 30 (2):  024202.  DOI: 10.1088/1674-1056/abcf3b Abstract ( 511 )   HTML ( 7 )   PDF (1201KB) ( 235 )   We study the abruptly autofocusing and autodefocusing properties of the circular Airy Gaussian vortex (CAiGV) beams in strongly nonlocal nonlinear medium for the first time through numerical simulations. The magnitude of topological charges and the position of the vortex could change not only the light spot pattern but also the intensity contrast. Meanwhile, we can change the position of the autofocusing and autodefocusing planes by changing the parameter of the incident beam. Furthermore, we can control the peak intensity contrast through choosing properly the truncation factor. As for the radiation force, we study the gradient and the scattering forces of CAiGV beams on Rayleigh dielectric sphere. Our analyses demonstrate that the radiation force can be enhanced by choosing proper parameters of CAiGV beams.

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Effects of initial electronic state on vortex patterns in counter-rotating circularly polarized attosecond pulses Qi Zhen(甄琪), Jia-He Chen(陈佳贺), Si-Qi Zhang(张思琪), Zhi-Jie Yang(杨志杰), and Xue-Shen Liu(刘学深) Chin. Phys. B, 2021, 30 (2):  024203.  DOI: 10.1088/1674-1056/abb7fb Abstract ( 545 )   HTML ( 3 )   PDF (2649KB) ( 136 )   We theoretically investigate the effects of different electronic states as the initial state on the vortex patterns in photoelectron momentum distributions (PMDs) from numerical solutions of the two-dimensional (2D) time-dependent Schrödinger equation (TDSE) of \(\rmHe^+\) with a pair of counter-rotating circularly polarized attosecond pulses. It is found that the number of spiral arms in vortex patterns is equal to the number of the absorbed photons when the initial state is the ground state. However, the number of spiral arms in vortex patterns is always two more than the number of the absorbed photons when the initial state is the excited state. This sensitivity is attributed to the initial electron density distribution. In addition, we have demonstrated the PMDs for different initial electronic states with the same wavelengths and analyzed their corresponding physical mechanisms. It is illustrated that the method presented can be employed to effectively control the distribution of the electron vortices.

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Ground-state cooling based on a three-cavity optomechanical system in the unresolved-sideband regime Jing Wang(王婧) Chin. Phys. B, 2021, 30 (2):  024204.  DOI: 10.1088/1674-1056/abc159 Abstract ( 361 )   HTML ( 5 )   PDF (575KB) ( 333 )   In the unresolved sideband regime, we propose a scheme for cooling mechanical resonator close to its ground state in a three-cavity optomechanical system, where the auxiliary cavities are indirectly connected with the mechanical resonator through standard optomechanical subsystem. The standard optomechanical subsystem is driven by a strong pump laser field. With the help of the auxiliary cavities, the heating process is suppressed and the cooling process of the mechanical resonator is enhanced. More importantly, the average phonon number is much less than 1 in a larger range. This means that the mechanical resonator can be cooled down to its ground state. All these interesting features will significantly promote the physical realization of quantum effects in multi-cavity optomechanical systems.

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Dynamic measurement of beam divergence angle of different fields of view of scanning lidar Qing-Yan Li(李青岩), Shi-Yu Yan(闫诗雨), Bin Zhang(张斌), and Chun-Hui Wang(王春晖) Chin. Phys. B, 2021, 30 (2):  024205.  DOI: 10.1088/1674-1056/abc155 Abstract ( 768 )   HTML ( 3 )   PDF (705KB) ( 181 )   The laser beam divergence angle is one of the important parameters to evaluate the quality of the laser beam. It can not only accurately indicate the nature of the beam divergence when the laser beam is transmitted over a long distance, but also objectively evaluate the performance of the laser system. At present, lidar has received a lot of attention as a core component of environment awareness technology. Micro-electromechanical system (MEMS) micromirror has become the first choice for three-dimensional imaging lidar because of its small size and fast scanning speed. However, due to the small size of the MEMS micromirror, the lidar scanning system has a small field of view (FOV). In order to achieve a wide range of scanning imaging, collimating optical system and wide-angle optical system are generally added to the system. However, due to the inherent properties of the optical lens, it is impossible to perfect the imaging, so the effects of collimating and expanding the beam will be different at different angles. This article aims to propose a measurement system that dynamically measures the divergence angles of MEMS scanning lidar beams in different fields of view to objectively evaluate the performances of scanning lidar systems.

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Polarization-independent silicon photonic grating coupler for large spatial light spots Lijun Yang(杨丽君), Xiaoyan Hu(胡小燕), Bin Li(李斌), and Jing Cao(曹静) Chin. Phys. B, 2021, 30 (2):  024206.  DOI: 10.1088/1674-1056/abbc00 Abstract ( 413 )   HTML ( 3 )   PDF (760KB) ( 85 )   We design and demonstrate a one-dimensional grating coupler with a low polarization-dependent loss (PDL) for large spatial light spots. Based on current fabrication conditions, we first utilize genetic algorithms to find the optimal grating structure including the distributions of duty and periods, making the effective refractive index of transverse electric mode the same as that of transverse magnetic mode. The designed grating coupler is fabricated on the common silicon-on-insulator platform and the PDL is measured to be within 0.41 dB covering the C-band.

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A novel plasmonic refractive index sensor based on gold/silicon complementary grating structure Xiangxian Wang(王向贤), Jiankai Zhu(朱剑凯), Yueqi Xu(徐月奇), Yunping Qi(祁云平), Liping Zhang(张丽萍), Hua Yang(杨华), and Zao Yi(易早) Chin. Phys. B, 2021, 30 (2):  024207.  DOI: 10.1088/1674-1056/abd690 Abstract ( 703 )   HTML ( 1 )   PDF (922KB) ( 193 )   A novel complementary grating structure is proposed for plasmonic refractive index sensing due to its strong resonance at near-infrared wavelength. The reflection spectra and the electric field distributions are obtained via the finite-difference time-domain method. Numerical simulation results show that multiple surface plasmon resonance modes can be excited in this novel structure. Subsequently, one of the resonance modes shows appreciable potential in refractive index sensing due to its wide range of action with the environment of the analyte. After optimizing the grating geometric variables of the structure, the designed structure shows the stable sensing performance with a high refractive index sensitivity of 1642 nm per refractive index unit (nm/RIU) and the figure of merit of 409 RIU-1. The promising simulation results indicate that such a sensor has a broad application prospect in biochemistry.

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Broadband absorption enhancement with ultrathin MoS2 film in the visible regime Jun Wu(吴俊) Chin. Phys. B, 2021, 30 (2):  024208.  DOI: 10.1088/1674-1056/abc3b5 Abstract ( 368 )   HTML ( 1 )   PDF (1416KB) ( 156 )   The broadband absorption enhancement effect in ultrathin molybdenum disulfide (MoS2) films is investigated. It is achieved by inserting the MoS2 film between a dielectric film and a one-dimensional silver grating backed with a silver mirror. The broadband absorption enhancement in the visible region is achieved, which exhibits large integrated absorption and short-circuit current density for solar energy under normal incidence. The optical properties of the proposed absorber are found to be superior to those of a reference planar structure, which makes the proposed structure advantageous for practical photovoltaic application. Moreover, the integrated absorption and short-circuit current density can be maintained high for a wide range of incident angles. A qualitative understanding of such broadband absorption enhancement effect is examined by illustrating the electromagnetic field distribution at some selected wavelengths. The results pave the way for developing high-performance optoelectronic devices, such as solar cells, photodetectors, and modulators.

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Theoretical research on terahertz wave generation from planar waveguide by optimized cascaded difference frequency generation Zhongyang Li(李忠洋), Jia Zhao(赵佳), Wenkai Liu(刘文锴), Qingfeng Hu(胡青峰), Yongjun Li(李永军), Binzhe Jiao(焦彬哲), Pibin Bing(邴丕彬), Hongtao Zhang(张红涛), Lian Tan(谭联), and Jianquan Yao(姚建铨) Chin. Phys. B, 2021, 30 (2):  024209.  DOI: 10.1088/1674-1056/abc3b7 Abstract ( 501 )   HTML ( 2 )   PDF (3821KB) ( 87 )   A novel scheme for high-efficiency terahertz (THz) wave generation based on optimized cascaded difference frequency generation (OCDFG) with planar waveguide is presented. The phase mismatches of each-order cascaded difference frequency generation (CDFG) are modulated by changing the thickness of the waveguide, resulting in a decrement of phase mismatches in cascaded Stokes processes and an increment of phase mismatches in cascaded anti-Stokes processes simultaneously. The modulated phase mismatches enhance the cascaded Stokes processes and suppress the cascaded anti-Stokes processes simultaneously, yielding energy conversion efficiencies over 25% from optical wave to THz wave at 100 K.

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Analysis of dark soliton generation in the microcavity with mode-interaction Xin Xu(徐昕), Xueying Jin(金雪莹), Jie Cheng(程杰), Haoran Gao(高浩然), Yang Lu(陆洋), and Liandong Yu(于连栋) Chin. Phys. B, 2021, 30 (2):  024210.  DOI: 10.1088/1674-1056/abc3b4 Abstract ( 454 )   HTML ( 1 )   PDF (771KB) ( 81 )   Mode-interaction plays an important role in the dark soliton generation in the microcavity. It is beneficial to the excitation of dark solitons, but also facilitates a variety of dark soliton states. Based on the non-normalized Lugiato-Lefever equation, the evolution of dark soliton in the microcavity with mode-interaction is investigated. By means of mode-interaction, the initial continuous wave (CW) field evolves into a dark soliton gradually, and the spectrum expands from a single mode to a broadband comb. After changing the mode-interaction parameters, the original modes which result in dual circular dark solitons inside the microcavity, are separated from the resonant mode by 2 free spectral ranges (FSR). When the initial field is another feasible pattern of weak white Gaussian noise, the large frequency detuning leads to the amplification of the optical power in the microcavity, and the mode-interaction becomes stronger. Then, multiple dark solitons, which correspond to the spectra with multi-FSR, can be excited by selecting appropriate mode-interaction parameters. In addition, by turning the mode-interaction parameters, the dark soliton number can be regulated, and the comb tooth interval in the spectrum also changes accordingly. Theoretical analysis results are significant for studying the dark soliton in the microcavity with mode-interaction.

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Efficient manipulation of terahertz waves by multi-bit coding metasurfaces and further applications of such metasurfaces Yunping Qi(祁云平) Baohe Zhang(张宝和), Jinghui Ding(丁京徽), Ting Zhang(张婷), Xiangxian Wang(王向贤), and Zao Yi(易早) Chin. Phys. B, 2021, 30 (2):  024211.  DOI: 10.1088/1674-1056/abd6fc Abstract ( 463 )   HTML ( 4 )   PDF (1505KB) ( 195 )   Benefiting from the unprecedented superiority of coding metasurfaces at manipulating electromagnetic waves in the microwave band, in this paper, we use the Pancharatnam-Berry (PB) phase concept to propose a high-efficiency reflective-type coding metasurface that can arbitrarily manipulate the scattering pattern of terahertz waves and implement many novel functionalities. By optimizing the coding sequences, we demonstrate that the designed 1-, 2-, and 3-bit coding metasurfaces with specific coding sequences have the strong ability to control reflected terahertz waves. The two proposed 1-bit coding metasurfaces demonstrate that the reflected terahertz beam can be redirected and arbitrarily controlled. For normally incident x-and y-polarized waves, a 10 dB radar cross-section (RCS) reduction can be achieved from 2.1 THz to 5.2 THz using the designed 2-bit coding metasurface. Moreover, two kinds of orbital angular momentum (OAM) vortex beams with different moduli are generated by a coding metasurface using different coding sequences. Our research provides a new degree of freedom for the sophisticated manipulation of terahertz waves, and contributes to the development of metasurfaces towards practical applications.

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Phase-sensitive Landau-Zener-Stückelberg interference in superconducting quantum circuit Zhi-Xuan Yang(杨智璇), Yi-Meng Zhang(张一萌), Yu-Xuan Zhou(周宇轩), Li-Bo Zhang(张礼博), Fei Yan(燕飞), Song Liu(刘松), Yuan Xu(徐源), and Jian Li(李剑) Chin. Phys. B, 2021, 30 (2):  024212.  DOI: 10.1088/1674-1056/abd753 Abstract ( 742 )   HTML ( 4 )   PDF (1157KB) ( 250 )   Superconducting circuit quantum electrodynamics (QED) architecture composed of superconducting qubit and resonator is a powerful platform for exploring quantum physics and quantum information processing. By employing techniques developed for superconducting quantum computing, we experimentally investigate phase-sensitive Landau-Zener-Stückelberg (LZS) interference phenomena in a circuit QED. Our experiments cover an extensive range of LZS transition parameters and demonstrate the LZS induced Rabi-like oscillation as well as phase-dependent steady-state population.

ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS

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Theoretical analysis and numerical simulation of acoustic waves in gas hydrate-bearing sediments Lin Liu(刘琳), Xiu-Mei Zhang(张秀梅), and Xiu-Ming Wang(王秀明) Chin. Phys. B, 2021, 30 (2):  024301.  DOI: 10.1088/1674-1056/abcf96 Abstract ( 403 )   HTML ( 5 )   PDF (2199KB) ( 162 )   Based on Carcione-Leclaire model, the time-splitting high-order staggered-grid finite-difference algorithm is proposed and constructed for understanding wave propagation mechanisms in gas hydrate-bearing sediments. Three compressional waves and two shear waves, as well as their energy distributions are investigated in detail. In particular, the influences of the friction coefficient between solid grains and gas hydrate and the viscosity of pore fluid on wave propagation are analyzed. The results show that our proposed numerical simulation algorithm proposed in this paper can effectively solve the problem of stiffness in the velocity-stress equations and suppress the grid dispersion, resulting in higher accuracy compared with the result of the Fourier pseudospectral method used by Carcione. The excitation mechanisms of the five wave modes are clearly revealed by the results of simulations. Besides, it is pointed that, the wave diffusion of the second kind of compressional and shear waves is influenced by the friction coefficient between solid grains and gas hydrate, while the diffusion of the third compressional wave is controlled by the fluid viscosity. Finally, two fluid-solid (gas-hydrate formation) models are constructed to study the mode conversion of various waves. The results show that the reflection, transmission, and transformation of various waves occur on the interface, forming a very complicated wave field, and the energy distribution of various converted waves in different phases is different. It is demonstrated from our studies that, the unconventional waves, such as the second and third kinds of compressional waves may be converted into conventional waves on an interface. These propagation mechanisms provide a concrete wave attenuation explanation in inhomogeneous media.

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Radiation force and torque on a two-dimensional circular cross-section of a non-viscous eccentric layered compressible cylinder in acoustical standing waves F G Mitri Chin. Phys. B, 2021, 30 (2):  024302.  DOI: 10.1088/1674-1056/abbbd9 Abstract ( 367 )   HTML ( 2 )   PDF (10104KB) ( 1176 )   The purpose of this study is to develop an analytical formalism and derive series expansions for the time-averaged force and torque exerted on a compound coated compressible liquid-like cylinder, insonified by acoustic standing waves having an arbitrary angle of incidence in the polar (transverse) plane. The host medium of wave propagation and the eccentric liquid-like cylinder are non-viscous. Numerical computations illustrate the theoretical analysis with particular emphases on the eccentricity of the cylinder, the angle of incidence and the dimensionless size parameters of the inner and coating cylindrical fluid materials. The method to derive the acoustical scattering, and radiation force and torque components conjointly uses modal matching with the addition theorem, which adequately account for the multiple wave interaction effects between the layer and core fluid materials. The results demonstrate that longitudinal and lateral radiation force components arise. Moreover, an axial radiation torque component is quantified and computed for the non-absorptive compound cylinder, arising from geometrical asymmetry considerations as the eccentricity increases. The computational results reveal the emergence of neutral, positive, and negative radiation force and torque depending on the size parameter of the cylinder, the eccentricity, and the angle of incidence of the insonifying field. Moreover, based on the law of energy conservation applied to scattering, numerical verification is accomplished by computing the extinction/scattering energy efficiency. The results may find some related applications in fluid dynamics, particle trapping, mixing and manipulation using acoustical standing waves.

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Effect of non-condensable gas on a collapsing cavitation bubble near solid wall investigated by multicomponent thermal MRT-LBM Yu Yang(杨雨), Ming-Lei Shan(单鸣雷), Qing-Bang Han(韩庆邦), and Xue-Fen Kan(阚雪芬) Chin. Phys. B, 2021, 30 (2):  024701.  DOI: 10.1088/1674-1056/abbbf8 Abstract ( 405 )   HTML ( 2 )   PDF (2586KB) ( 63 )   A multicomponent thermal multi-relaxation-time (MRT) lattice Boltzmann method (LBM) is presented to study collapsing cavitation bubble. The simulation results satisfy Laplace law and the adiabatic law, and are consistent with the numerical solution of the Rayleigh-Plesset equation. To study the effects of the non-condensable gas inside bubble on collapsing cavitation bubble, a numerical model of single spherical bubble near a solid wall is established. The temperature and pressure evolution of the two-component two-phase flow are well captured. In addition, the collapse process of the cavitation bubble is discussed elaborately by setting the volume fractions of the gas and vapor to be the only variables. The results show that the non-condensable gas in the bubble significantly affects the pressure field, temperature field evolution, collapse velocity, and profile of the bubble. The distinction of the pressure and temperature on the wall after the second collapse becomes more obvious as the non-condensable gas concentration increases.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

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Analysis of asymmetry of the Dα emission spectra under the Zeeman effect in boundary region for D-D experiment on EAST tokamak Wei Gao(高伟), Juan Huang(黄娟), Jianxun Su(宿建勋), Jing Fu(付静), Yingjie Chen(陈颖杰), Wei Gao(高伟), Zhenwei Wu(吴振伟), and EAST Team Chin. Phys. B, 2021, 30 (2):  025201.  DOI: 10.1088/1674-1056/abc162 Abstract ( 383 )   HTML ( 1 )   PDF (1172KB) ( 201 )   In 2015 campaign, deuterium atomic emission spectra (Dα ) under the Zeeman effect in boundary region had been measured by a high resolution optical spectroscopic multichannel analysis (OSMA) system based on passive spectroscopy during the deuterium plasma discharge on EAST tokamak, and part of the works about the Zeeman effect on Dα spectra had already been done. However, the asymmetric phenomena of Dα emission spectra under the Zeeman effect were observed in process of analyzing the spectral data. To understand the asymmetric phenomena and acquire the useful local plasma information, an algorithm was proposed and used to analyze the asymmetry of the emission spectra under the Zeeman effect with all polarization components (π and σ). In the algorithm, the neutral atoms were considered to follow the Maxwell distribution on EAST, and I + σ ≠ I-σ was considered and set. Because of the line-averaged spectra along the viewing chord, the emission spectra were considered from two different regions: low-field side (LFS) and high-field side (HFS). Each spectral line was classified into three energy categories (the cold, warm, and hot) based on different atomic production processes in boundary recycling. The viewing angle θ (between the magnetic field B and the viewing chord), magnetic field B at two spectral emission positions (HFS and LFS) and the Doppler shift of all three energy categories of each spectral line were all considered in the algorithm. The effect of instrument function was also included here. The information of the boundary plasma were acquired, the reason for the asymmetric phenomena was discussed, and the boundary recycling during the discharge were studied in the paper. Based on fitting a statistical data of acquired fitting results, an important conclusion was acquired that the ratio of the spectral line intensity in HFS and LFS was proportional to the square of that of the corresponding magnetic field.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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CdS/Si nanofilm heterojunctions based on amorphous silicon films: Fabrication, structures, and electrical properties Yong Li(李勇), Peng-Fei Ji(姬鹏飞), Yue-Li Song(宋月丽), Feng-Qun Zhou(周丰群), Hong-Chun Huang(黄宏春), and Shu-Qing Yuan(袁书卿) Chin. Phys. B, 2021, 30 (2):  026101.  DOI: 10.1088/1674-1056/abc15e Abstract ( 354 )   HTML ( 3 )   PDF (809KB) ( 216 )   Shortening the distance between the depletion region and the electrodes to reduce the trapped probability of carriers is a useful approach for improving the performance of heterojunction. The CdS/Si nanofilm heterojunctions are fabricated by using the radio frequency magnetron sputtering method to deposit the amorphous silicon nanofilms and CdS nanofilms on the ITO glass in turn. The relation of current density to applied voltage (I-V) shows the obvious rectification effect. From the analysis of the double logarithm I-V curve it follows that below ∼ 2.73 V the electron behaviors obey the Ohmic mechanism and above ∼ 2.73 V the electron behaviors conform to the space charge limited current (SCLC) mechanism. In the SCLC region part of the traps between the Fermi level and conduction band are occupied, and with the increase of voltage most of the traps are occupied. It is believed that CdS/Si nanofilm heterojunction is a potential candidate in the field of nano electronic and optoelectronic devices by optimizing its fabricating procedure.

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Understanding defect production in an hcp Zr crystal upon irradiation: An energy landscape perspective Jiting Tian(田继挺) Chin. Phys. B, 2021, 30 (2):  026102.  DOI: 10.1088/1674-1056/abbbe0 Abstract ( 300 )   HTML ( 1 )   PDF (1006KB) ( 74 )   Primary radiation damage in hcp Zr, including both defect production in a single collision cascade and damage buildup through cascade overlap, is investigated using molecular dynamics (MD) simulations from a potential energy landscape (PEL) perspective. It is found that the material's response to an energetic particle can be understood as a trajectory in the PEL comprising a fast uphill journey and a slow downhill one. High-temperature-induced damage reduction and the difference in the radiation tolerance between metals and semiconductors can be both qualitatively explained by the dynamics of the trajectory associated with the topographic features of the system's PEL. Additionally, by comparing irradiation and heating under a nearly identical condition, we find that large atomic displacements stemming from the extreme locality of the energy deposition in irradiation events are the key factor leading to radiation damage in a solid. Finally, we discuss the advantages of the PEL perspective and suggest that a combination of the PEL and the traditional crystallographic methods may provide more insights in future work.

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Characterization, spectroscopic investigation of defects by positron annihilation, and possible application of synthesized PbO nanoparticles Sk Irsad Ali, Anjan Das, Apoorva Agrawal, Shubharaj Mukherjee, Maudud Ahmed, P M G Nambissan, Samiran Mandal, and Atis Chandra Mandal Chin. Phys. B, 2021, 30 (2):  026103.  DOI: 10.1088/1674-1056/abd2a9 Abstract ( 480 )   HTML ( 6 )   PDF (1605KB) ( 145 )   Nanocrystalline samples of highly pure lead oxide were prepared by the sol-gel route of synthesis. X-ray diffraction and transmission electron microscopic techniques confirmed the nanocrystallinity of the samples, and the average sizes of the crystallites were found within 20 nm to 35 nm. The nanocrystallites exhibited specific anomalous properties, among which a prominent one is the increased lattice parameters and unit cell volumes. The optical band gaps also increased when the nanocrystallites became smaller in size. The latter aspect is attributable to the onset of quantum confinement effects, as seen in a few other metal oxide nanoparticles. Positron annihilation was employed to study the vacancy type defects, which were abundant in the samples and played crucial roles in modulating their properties. The defect concentrations were significantly larger in the samples of smaller crystallite sizes. The results suggested the feasibility of tailoring the properties of lead oxide nanocrystallites for technological applications, such as using lead oxide nanoparticles in batteries for better performance in discharge rate and resistance. It also provided the physical insight into the structural build-up process when crystallites were formed with a finite number of atoms, whose distributions were governed by the site stabilization energy.

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Space symmetry of effective physical constants for biaxial crystals Fuan Liu(刘孚安), Zeliang Gao(高泽亮), XinYin(尹鑫), and Xutang Tao(陶绪堂) Chin. Phys. B, 2021, 30 (2):  026104.  DOI: 10.1088/1674-1056/abcf99 Abstract ( 349 )   HTML ( 1 )   PDF (969KB) ( 207 )   In eight quadrants, the positive and negative signs of tensor components describing physical properties of biaxial crystals have been given. The distributions of the physical properties described with different order tensors and their space symmetries have been discussed. These results show that the distributions of effective physical constants are symmetrical in the eight quadrants for the orthorhombic system, but there are two and four kinds of distributions for monoclinic and triclinic systems respectively. Thence, to avoid ambiguities and difficulties in characterizing and applying properties of biaxial crystals, we suggest that the really positive directions of the coordinate axes should be defined before the measurements of their physical properties and their device applications.

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Mechanically tunable broadband terahertz modulator based on high-aligned Ni nanowire arrays Wenfeng Xiang(相文峰), Xuan Liu(刘旋), Xiaowei Huang(黄晓炜), Qingli Zhou(周庆莉), Haizhong Guo(郭海中), and Songqing Zhao(赵嵩卿) Chin. Phys. B, 2021, 30 (2):  026201.  DOI: 10.1088/1674-1056/abd6f5 Abstract ( 430 )   HTML ( 1 )   PDF (1031KB) ( 163 )   We present a mechanically tunable broadband terahertz (THz) modulator based on the high-aligned Ni nanowire (NW) arrays. The modulator is a sandwich structure consisting of two polydimethylsiloxane layers and a central layer of high-aligned Ni NW arrays. Our experimental measurements reveal the transmittance of THz wave can be effectively modulated by mechanical stretching. The NW density in arrays increases with the strain increasing, which induced an enhancement in the absorption of THz wave. When the strain increases from 0 to 6.5%, a linear relationship is observed for the variation of modulation depth (MD) of THz wave regarding the strain, and the modulated range is from 0 to 85% in a frequency range from 0.3 THz to 1.8 THz. Moreover, the detectable MD is about 15% regarding the 1% strain change resolution. This flexible Ni NW-based modulator can be promised many applications, such as remote strain sensing, and wearable devices.

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First-principles study of the co-effect of carbon doping and oxygen vacancies in ZnO photocatalyst Jia Shi(史佳), Lei Wang(王蕾), and Qiang Gu(顾强) Chin. Phys. B, 2021, 30 (2):  026301.  DOI: 10.1088/1674-1056/abc0db Abstract ( 393 )   HTML ( 3 )   PDF (1555KB) ( 74 )   Although tuning band structure of optoelectronic semiconductor-based materials by means of doping single defect is an important approach for potential photocatalysis application, C-doping or oxygen vacancy (Vo) as a single defect in ZnO still has limitations for photocatalytic activity. Meanwhile, the influence of co-existence of various defects in ZnO still lacks sufficient studies. Therefore, we investigate the photocatalytic properties of ZnOxC0.0625 (x = 0.9375, 0.875, 0.8125), confirming that the co-effect of various defects has a greater enhancement for photocatalytic activity driven by visible-light than the single defect in ZnO. To clarify the underlying mechanism of co-existence of various defects in ZnO, we perform systematically the electronic properties calculations using density functional theory. It is found that the co-effect of C-doping and Vo in ZnO can achieve a more controllable band gap than doping solely in ZnO. Moreover, the impact of the effective masses of ZnOxC0.0625 (x = 0.9375, 0.875, 0.8125) is also taken into account. In comparison with heavy Vo concentrations, the light Vo concentration (x=0.875) as the optimal component together with C-doping in ZnO, can significantly improve the visible-light absorption and benefit photocatalytic activity.

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Internal friction behavior of Zr59Fe18Al10Ni10Nb3 metallic glass under different aging temperatures Israa Faisal Ghazi, Israa Meften Hashim, Aravindhan Surendar, Nalbiy Salikhovich Tuguz, Aseel M. Aljeboree, Ayad F. Alkaim, and Nisith Geetha Chin. Phys. B, 2021, 30 (2):  026401.  DOI: 10.1088/1674-1056/abc14f Abstract ( 494 )   HTML ( 1 )   PDF (1259KB) ( 86 )   We investigate the role of aging temperature on relaxation of internal friction in Zr59Fe18Al10Ni10Nb3 metallic glass. For this purpose, dynamic mechanical analysis with different annealing temperatures and frequency values is applied. The results indicate that the aging process leads to decrease in the dissipated energy in the temperature range of glass transition. It is also found that the increase in applied frequency weakens the loss factor intensity in the metallic glass. Moreover, the Kohlrausch-Williams-Watts (KWW) equation is used to evaluate the evolution of internal friction during the aging process. According to the results, higher annealing temperature will make the primary internal friction in the material increase; however, a sharp decline is observed with the time. The drop in characteristic time of internal friction is also closely correlated to the rate of atomic rearrangement under the dynamic excitation so that at higher annealing temperatures, the driving force for the collaborative movement of atoms is easily provided and the mean relaxation time significantly decreases.

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Quench dynamics in 1D model with 3rd-nearest-neighbor hoppings Shuai Yue(岳帅), Xiang-Fa Zhou(周祥发), and Zheng-Wei Zhou(周正威) Chin. Phys. B, 2021, 30 (2):  026402.  DOI: 10.1088/1674-1056/abd742 Abstract ( 581 )   HTML ( 4 )   PDF (1731KB) ( 184 )   The non-equilibrium dynamics of a one-dimensional (1D) topological system with 3rd-nearest-neighbor hopping has been investigated by analytical and numerical methods. An analytical form of topological defect density under the periodic boundary conditions (PBC) is obtained by using the Landau-Zener formula (LZF), which is consistent with the scaling of defect production provided by the Kibble-Zurek mechanism (KZM). Under the open boundary conditions (OBC), quench dynamics becomes more complicated due to edge states. The behaviors of the system quenching across different phases show that defect production no longer satisfies the KZM paradigm since complicated couplings exist under OBC. Some new dynamical features are revealed.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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First-principles study of co-adsorption behavior of O2 and CO2 molecules on δ -Pu(100) surface Chun-Bao Qi(戚春保), Tao Wang(王涛), Ru-Song Li(李如松), Jin-Tao Wang(王金涛), Ming-Ao Qin(秦铭澳), and Si-Hao Tao(陶思昊) Chin. Phys. B, 2021, 30 (2):  026601.  DOI: 10.1088/1674-1056/abc158 Abstract ( 474 )   HTML ( 3 )   PDF (2829KB) ( 188 )   First principles calculation is performed to study the co-adsorption behaviors of O2 and CO2 on δ -Pu(100) surface by using a slab model within the framework of density functional theory (DFT). The results demonstrate that the most favorable co-adsorption configurations are T v-C4O7 and T p1-C2O8, with adsorption energy of -17.296 eV and -23.131 eV for CO2-based and O2-based system, respectively. The C and O atoms mainly interact with the Pu surface atoms. Furthermore, the chemical bonding between C/O and Pu atom is mainly of ionic state, and the reaction mechanism is that C 2s, C 2p, O 2s, and O 2p orbitals overlap and hybridize with Pu 6p, Pu 6d, and Pu 5f orbital, resulting in the occurrence of new band structure. The adsorption and dissociation of CO2 molecule are obviously promoted by preferentially occupying adsorbed O atoms, therefore, a potential CO2 protection mechanism for plutonium-based materials is that in CO2 molecule there occurs complete dissociation of CO\(_2\to \)C+O+O, then the dissociated C atom combines with O atom from O2 dissociation and produces CO, which will inhibit the O2 from further oxidizing Pu surface, and slow down the corrosion rate of plutonium-based materials.

SPECIAL TOPIC—Quantum computation and quantum simulation

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Cluster mean-field study of spinor Bose-Hubbard ladder: Ground-state phase diagram and many-body population dynamics Li Zhang(张莉), Wenjie Liu(柳文洁), Jiahao Huang(黄嘉豪), and Chaohong Lee(李朝红) Chin. Phys. B, 2021, 30 (2):  026701.  DOI: 10.1088/1674-1056/abd760 Abstract ( 533 )   HTML ( 5 )   PDF (2374KB) ( 236 )   We present a cluster mean-field study for ground-state phase diagram and many-body dynamics of spin-1 bosons confined in a two-chain Bose-Hubbard ladder (BHL). For unbiased BHL, we find superfluid (SF) phase and integer filling Mott insulator (IntMI) phase. For biased BHL, in addition to the SF and IntMI phases, there appears half-integer filling Mott insulator (HIntMI) phase. The phase transition between the SF and IntMI phases can be first order at a part of phase boundaries, while the phase transition between the SF and HIntMI phases is always second order. By tuning the bias energy, we report on the change of the nature of SF-MI phase transitions. Furthermore, we study the effect of the spin-dependent interaction on the many-body population dynamics. The spin-dependent interaction can lead to rich dynamical behaviors, but does not influence the particle transfer efficiency. Our results indicate a way to tune the nature of the SF-MI phase transition and open a new avenue to study the many-body dynamics of spinor bosons in optical lattices.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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Atomistic simulations on adhesive contact of single crystal Cu and wear behavior of Cu-Zn alloy You-Jun Ye(叶有俊), Le Qin (秦乐), Jing Li (李京), Lin Liu(刘麟), and Ling-Kang Wu(吴凌康) Chin. Phys. B, 2021, 30 (2):  026801.  DOI: 10.1088/1674-1056/abbbf6 Abstract ( 425 )   HTML ( 1 )   PDF (1336KB) ( 63 )   Atomistic simulations are carried out to investigate the nano-indentation of single crystal Cu and the sliding of the Cu-Zn alloy. As the contact zone is extended due to adhesive interaction between the contact atoms, the contact area on a nanoscale is redefined. A comparison of contact area and contact force between molecular dynamics (MD) and contact theory based on Greenwood-Williamson (GW) model is made. Lower roughness causes the adhesive interaction to weaken, showing the better consistency between the calculated results by MD and those from the theoretical model. The simulations of the sliding show that the substrate wear decreases with the mol% of Zn increasing, due to the fact that the diffusion movements of Zn atoms in substrate are blocked during the sliding because of the hexagonal close packed (hcp) structure of Zn.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

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Strain and interfacial engineering to accelerate hydrogen evolution reaction of two-dimensional phosphorus carbide Tao Huang(黄韬), Yuan Si(思源), Hong-Yu Wu(吴宏宇), Li-Xin Xia(夏立新), Yu Lan(蓝郁), Wei-Qing Huang(黄维清), Wang-Yu Hu(胡望宇), and Gui-Fang Huang(黄桂芳) Chin. Phys. B, 2021, 30 (2):  027101.  DOI: 10.1088/1674-1056/abbbe7 Abstract ( 427 )   HTML ( 1 )   PDF (3057KB) ( 116 )   Hydrogen, regarded as a promising energy carrier to alleviate the current energy crisis, can be generated from hydrogen evolution reaction (HER), whereas its efficiency is impeded by the activity of catalysts. Herein, effective strategies, such as strain and interfacial engineering, are imposed to tune the catalysis performance of novel two-dimensional (2D) phosphorus carbide (PC) layers using first-principle calculations. The findings show that P site in pristine monolayer PC (ML-PC) exhibits higher HER performance than C site. Intriguingly, constructing bilayer PC sheet (BL-PC) can change the coordinate configuration of P atom to form 3-coordination-P atom (3-co-P) and 4-coordination-P atom (4-co-P), and the original activity of 3-co-P site is higher than the 4-co-P site. When an external compressive strain is applied, the activity of the 4-co-P site is enhanced whereas the external strain can barely affect that of 3-co-P site. Interestingly, the graphene substrate enhances the overall activity of the BL-PC because the graphene substrate optimizes the ∆ G H* value of 4-co-P site, although it can barely affect the HER activity of 3-co-P site and ML-PC. The desirable properties render 2D PC-based material promising candidates for HER catalysts and shed light on the wide utilization in electrocatalysis.

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Modeling, simulations, and optimizations of gallium oxide on gallium-nitride Schottky barrier diodes Tao Fang(房涛), Ling-Qi Li(李灵琪), Guang-Rui Xia(夏光睿), and Hong-Yu Yu(于洪宇) Chin. Phys. B, 2021, 30 (2):  027301.  DOI: 10.1088/1674-1056/abc0dd Abstract ( 941 )   HTML ( 18 )   PDF (600KB) ( 522 )   With technology computer-aided design (TCAD) simulation software, we design a new structure of gallium oxide on gallium-nitride Schottky barrier diode (SBD). The parameters of gallium oxide are defined as new material parameters in the material library, and the SBD turn-on and breakdown behavior are simulated. The simulation results reveal that this new structure has a larger turn-on current than Ga2O3 SBD and a larger breakdown voltage than GaN SBD. Also, to solve the lattice mismatch problem in the real epitaxy, we add a ZnO layer as a transition layer. The simulations show that the device still has good properties after adding this layer.

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Novel fast-switching LIGBT with P-buried layer and partial SOI Haoran Wang(王浩然), Baoxing Duan(段宝兴), Licheng Sun(孙李诚), and Yintang Yang(杨银堂) Chin. Phys. B, 2021, 30 (2):  027302.  DOI: 10.1088/1674-1056/abcf3e Abstract ( 484 )   HTML ( 2 )   PDF (776KB) ( 168 )   A novel silicon-on-insulator lateral insulated gate bipolar transistor (SOI LIGBT) is proposed in this paper. The proposed device has a P-type buried layer and a partial-SOI layer, which is called the BPSOI-LIGBT. Due to the electric field modulation effect generated by the P-type buried layer and the partial-SOI layer, the proposed structure generates two new peaks in the surface electric field distribution, which can achieve a smaller device size with a higher breakdown voltage. The smaller size of the device is beneficial to the fast switching. The simulation shows that under the same size, the breakdown voltage of the BPSOI LIGBT is 26% higher than that of the conventional partial-SOI LIGBT (PSOI LIGBT), and 84% higher than the traditional SOI LIGBT. When the forward voltage drop is 2.05 V, the turn-off time of the BPSOI LIGBT is 71% shorter than that of the traditional SOI LIGBT. Therefore, the proposed BPSOI LIGBT has a better forward voltage drop and turn-off time trade-off than the traditional SOI LIGBT. In addition, the BPSOI LIGBT effectively relieves the self-heating effect of the traditional SOI LIGBT.

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Analysis of the decrease of two-dimensional electron gas concentration in GaN-based HEMT caused by proton irradiation Jin-Jin Tang(汤金金), Gui-Peng Liu(刘贵鹏), Jia-Yu Song(宋家毓), Gui-Juan Zhao(赵桂娟), and Jian-Hong Yang(杨建红) Chin. Phys. B, 2021, 30 (2):  027303.  DOI: 10.1088/1674-1056/abbbf7 Abstract ( 468 )   HTML ( 3 )   PDF (761KB) ( 159 )   Gallium nitride (GaN)-based high electron mobility transistors (HEMTs) that work in aerospace are exposed to particles radiation, which can cause the degradation in electrical performance. We investigate the effect of proton irradiation on the concentration of two-dimensional electron gas (2DEG) in GaN-based HEMTs. Coupled Schrödinger's and Poisson's equations are solved to calculate the band structure and the concentration of 2DEG by the self-consistency method, in which the vacancies caused by proton irradiation are taken into account. Proton irradiation simulation for GaN-based HEMT is carried out using the stopping and range of ions in matter (SRIM) simulation software, after which a theoretical model is established to analyze how proton irradiation affects the concentration of 2DEG. Irradiated by protons with high fluence and low energy, a large number of Ga vacancies appear inside the device. The results indicate that the ionized Ga vacancies in the GaN cap layer and the AlGaN layer will affect the Fermi level, while the Ga vacancies in the GaN layer will trap the two-dimensional electrons in the potential well. Proton irradiation significantly reduced the concentration of 2DEG by the combined effect of these two mechanisms.

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Characterization of low-resistance ohmic contacts to heavily carbon-doped n-type InGaAsBi films treated by rapid thermal annealing Shu-Xing Zhou(周书星), Li-Kun Ai(艾立鹍), Ming Qi(齐鸣), An-Huai Xu(徐安怀), Jia-Sheng Yan(颜家圣), Shu-Sen Li(李树森), and Zhi Jin(金智) Chin. Phys. B, 2021, 30 (2):  027304.  DOI: 10.1088/1674-1056/abcf97 Abstract ( 432 )   HTML ( 1 )   PDF (615KB) ( 138 )   Carbon-doped InGaAsBi films on InP:Fe (100) substrates have been grown by gas source molecular beam epitaxy (GSMBE). The electrical properties and non-alloyed Ti/Pt/Au contact resistance of n-type carbon-doped InGaAsBi films were characterized by Van der Pauw-Hall measurement and transmission line method (TLM) with and without rapid thermal annealing (RTA). It was found that the specific contact resistance decreases gradually with the increase of carrier concentration. The electron concentration exhibits a sharp increase, and the specific contact resistance shows a noticeable reduction after RTA. With RTA, the InGaAsBi film grown under CBr4 supply pressure of 0.18 Torr exhibited a high electron concentration of 1.6× 1021 cm-3 and achieved an ultra-low specific contact resistance of 1× 10-8 Ω cm2, revealing that contact resistance depends greatly on the tunneling effect.

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A first-principles study on zigzag phosphorene nanoribbons terminated by transition metal atoms Shuai Yang(杨帅), Zhiyong Wang(王志勇), Xueqiong Dai(戴学琼), Jianrong Xiao(肖剑荣), and Mengqiu Long(龙孟秋) Chin. Phys. B, 2021, 30 (2):  027305.  DOI: 10.1088/1674-1056/abc0e1 Abstract ( 480 )   HTML ( 1 )   PDF (662KB) ( 180 )   We have investigated the electronic and magnetic properties of zigzag phosphorene nanoribbons (ZPNRs) with transition metal (TM) passivated atoms, it can be found that the ZPNRs with TM passivated atoms exhibit different magnetisms except for the Ni-passivated system. Meanwhile, the results show that the magnetic moments of ZPNRs with TM passivated atoms are larger than that of ZPNRs with other passivated non-metals/groups. Interestingly, it can be found that Fe-passivated ZPNR exhibits magnetic semiconducting character, which provides the possbility for the application of phosphorene in information storage. For Mn-passivated ZPNRs, it exhibits the half-metallicity. These results may be useful for potential applications of phosphorene in electronic and high-performance spintronic devices.

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Superconducting anisotropy and vortex pinning in CaKFe4As4 and KCa2Fe4As4F2 Hot! A B Yu(于奥博), Z Huang(黄喆), C Zhang(张驰), Y F Wu(吴宇峰), T Wang(王腾), T Xie(谢涛), C Liu(刘畅), H Li(李浩), W Peng(彭炜), H Q Luo(罗会仟), G Mu(牟刚), H Xiao(肖宏), L X You(尤立星), and T Hu(胡涛) Chin. Phys. B, 2021, 30 (2):  027401.  DOI: 10.1088/1674-1056/abcf98 Abstract ( 884 )   HTML ( 4 )   PDF (1531KB) ( 361 )   The vortex pinning determining the current carrying capacity of a superconductor is an important property to the applications of superconducting materials. For layered superconductors, the vortex pinning can be enhanced by a strong interlayer interaction in accompany with a suppression of superconducting anisotropy, which remains to be investigated in iron based superconductors (FeSCs) with the layered structure. Here, based on the transport and magnetic torque measurements, we experimentally investigate the vortex pinning in two bilayer FeSCs, CaKFe4As4(Fe1144) and KCa2Fe4As4F2(Fe12442), and compare their superconducting anisotropy γ. While the anisotropy γ ≈ 3 for Fe1144 is much smaller than γ ≈ 15 in Fe12442 around T c, a higher flux pinning energy as evidenced by a higher critical current density is found in Fe1144, as compared with the case of Fe12442. In combination with the literature data of Ba0.72K0.28Fe2As2 and NdFeAsO0.82F0.18, we reveal an anti-correlation between the pinning energy and the superconducting anisotropy in these FeSCs. Our results thus suggest that the interlayer interaction can not be neglected when considering the vortex pinning in FeSCs.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

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Field-induced N\'eel vector bi-reorientation of a ferrimagnetic insulator in the vicinity of compensation temperature Peng Wang(王鹏), Hui Zhao(赵辉), Zhongzhi Luan(栾仲智), Siyu Xia(夏思宇), Tao Feng(丰韬), and Lifan Zhou(周礼繁) Chin. Phys. B, 2021, 30 (2):  027501.  DOI: 10.1088/1674-1056/abbbef Abstract ( 441 )   HTML ( 1 )   PDF (834KB) ( 143 )   The spin Hall magnetoresistance (SMR) effect in Pt/Gd3Fe5O12 (GdIG) bilayers was systematically investigated. The sign of SMR changes twice with increasing magnetic field in the vicinity of the magnetization compensation point (T M) of GdIG. However, conventional SMR theory predicts the invariant SMR sign in the heterostructure composed of a heavy metal film in contact with a ferromagnetic or antiferromagnetic film. We conclude that this is because of the significant enhancement of the magnetic moment of the Gd sub-lattice and the unchanged moment of the Fe sub-lattice with a relatively large field, meaning that a small net magnetic moment is induced at T M. As a result, the N\'eel vector aligns with the field after the spin-flop transition, meaning that a bi-reorientation of the N\'eel vector is produced. Theoretical calculations based on the N\'eel's theory and SMR theory also support our conclusions. Our findings indicate that the N\'eel-vector direction of a ferrimagnet can be tuned across a wide range by a relatively low external field around T M.

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Close-coupled nozzle atomization integral simulation and powder preparation using vacuum induction gas atomization technology Peng Wang(汪鹏), Jing Li(李静), Xin Wang(王欣), Heng-San Liu(刘恒三), Bin Fan(范斌), Ping Gan(甘萍), Rui-Feng Guo(郭瑞峰), Xue-Yuan Ge(葛学元), and Miao-Hui Wang(王淼辉) Chin. Phys. B, 2021, 30 (2):  027502.  DOI: 10.1088/1674-1056/abc167 Abstract ( 823 )   HTML ( 12 )   PDF (6154KB) ( 732 )   We simulate the gas-atomization process of a close-coupled annular nozzle for vacuum induction gas atomization at a three-dimensional scale. Moreover, the relationship between the simulated droplet type and experimentally metallic powder is established by comparing the morphology of droplets with powders. Herein, the primary atomization process is described by the volume-of-fluid (VOF) approach, whereas the prediction of powder diameter after secondary atomization is realized by the VOF-Lagrangian method. In addition, to completely reflect the breaking and deformation process of the metallic flow, we employ the VOF model to simulate the secondary atomization process of a single ellipsoidal droplet. The results show that the primary atomization process includes the formation of surface liquid film, appearance of serrated ligaments, and shredding of ligaments. Further, gas recirculation zone plays an important role in formation of the umbrella-shaped liquid film. The secondary atomization process is divided into droplet convergence and dispersion stages, and the predicted powder diameter is basically consistent with the experiment. In general, the four main powder shapes are formed by the interaction of five different typical droplets.

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Coercivity and microstructure of sintered Nd-Fe-B magnets diffused with Pr-Co, Pr-Al, and Pr-Co-Al alloys Lei Jin(金磊), Zhe-Huan Jin(金哲欢), Jin-Hao Zhu(朱金豪), Guang-Fei Ding(丁广飞), Bo Zheng(郑波) , Shuai Guo(郭帅), Ren-Jie Chen(陈仁杰), A-Ru Yan(闫阿儒), and Xin-Cai Liu(刘新才) Chin. Phys. B, 2021, 30 (2):  027503.  DOI: 10.1088/1674-1056/abc166 Abstract ( 585 )   HTML ( 8 )   PDF (1886KB) ( 246 )   The commercial 42M Nd-Fe-B magnet was treated by grain boundary diffusion (GBD) with Pr70Co30 (PC), Pr70Al30 (PA) and Pr70Co15Al15 (PCA) alloys, respectively. The mechanism of coercivity enhancement in the GBD magnets was investigated. The coercivity was enhanced from 1.63 T to 2.15 T in the PCA GBD magnet, higher than the 1.81 T of the PC GBD magnet and the 2.01 T of the PA GBD magnet. This indicates that the joint addition of Co and Al in the diffusion source can further improve the coercivity. Microstructural investigations show that the coercivity enhancement is mainly attributed to the exchange-decoupling of the GB phases. In the PCA GBD magnet, the wider thin GB phases can be formed and the thin GB phases can still be observed at the diffusion depth of 1500 μ m due to the combined action of Co and Al. At the same time, the formation of the Pr-rich shell can also be observed, which is helpful for the coercivity enhancement.

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High-frequency magnetic properties and core loss of carbonyl iron composites with easy plane-like structures Guo-Wu Wang(王国武), Chun-Sheng Guo(郭春生), Liang Qiao(乔亮), Tao Wang(王涛), and Fa-Shen Li(李发伸) Chin. Phys. B, 2021, 30 (2):  027504.  DOI: 10.1088/1674-1056/abc15c Abstract ( 448 )   HTML ( 0 )   PDF (1585KB) ( 114 )   To fully release the potential of wide bandgap (WBG) semiconductors and achieve high energy density and efficiency, a carbonyl iron soft magnetic composite (SMC) with an easy plane-like structure is prepared. Due to this structure, the permeability of the composite increases by 3 times (from 7.5 to 21.5) at 100 MHz compared with to the spherical carbonyl iron SMC, and the permeability changes little at frequencies below 100 MHz. In addition, the natural resonance frequency of the composite shifts to higher frequencies at 1.7 GHz. The total core losses of the composites at 10, 20, and 30 mT are 80.0, 355.3, and 810.7 mW/cm3, respectively, at 500 kHz. Compared with the spherical carbonyl iron SMC, the core loss at 500 kHz is reduced by more than 60%. Therefore, this kind of soft magnetic composite with an easy plane-like structure is a good candidate for unlocking the potential of WBG semiconductors and developing the next-generation power electronics.

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Evolution of domain structure in Fe3GeTe2 Hot! Siqi Yin(尹思琪), Le Zhao(赵乐), Cheng Song(宋成), Yuan Huang(黄元), Youdi Gu(顾有地), Ruyi Chen(陈如意), Wenxuan Zhu(朱文轩), Yiming Sun(孙一鸣), Wanjun Jiang(江万军), Xiaozhong Zhang(章晓中), and Feng Pan(潘峰) Chin. Phys. B, 2021, 30 (2):  027505.  DOI: 10.1088/1674-1056/abd693 Abstract ( 1003 )   HTML ( 10 )   PDF (1057KB) ( 1044 )   Two-dimensional (2D) magnets provide an ideal platform to explore new physical phenomena in fundamental magnetism and to realize the miniaturization of magnetic devices. The study on its domain structure evolution with thickness is of great significance for better understanding the 2D magnetism. Here, we investigate the magnetization reversal and domain structure evolution in 2D ferromagnet Fe3GeTe2 (FGT) with a thickness range of 11.2-112 nm. Three types of domain structures and their corresponding hysteresis loops can be obtained. The magnetic domain varies from a circular domain via a dendritic domain to a labyrinthian domain with increasing FGT thickness, which is accompanied by a transition from squared to slanted hysteresis loops with reduced coercive fields. These features can be ascribed to the total energy changes from exchange interaction-dominated to dipolar interaction-dominated with increasing FGT thickness. Our finding not only enriches the fundamental magnetism, but also paves a way towards spintronics based on 2D magnet.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

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Sr-doping effects on conductivity, charge transport, and ferroelectricity of Ba0.7La0.3TiO3 epitaxial thin films Qiang Li(李强), Dao Wang(王岛), Yan Zhang(张岩), Yu-Shan Li(李育珊), Ai-Hua Zhang(张爱华), Rui-Qiang Tao(陶瑞强), Zhen Fan(樊贞), Min Zeng(曾敏), Guo-Fu Zhou(周国富), Xu-Bing Lu(陆旭兵), and Jun-Ming Liu(刘俊明) Chin. Phys. B, 2021, 30 (2):  027701.  DOI: 10.1088/1674-1056/abc15a Abstract ( 408 )   HTML ( 0 )   PDF (1352KB) ( 113 )   Sr-doped Ba0.7La0.3TiO3 (BSLTO) thin films are deposited by pulsed laser deposition, and their microstructure, conductivity, carrier transport mechanism, and ferroelectricity are systematically investigated. The x-ray diffraction measurements demonstrate that Sr-doping reduces the lattice constant of BSLTO thin films, resulting in the enhanced phonon energy in the films as evidenced by the Raman measurements. Resistivity-temperature and Hall effect measurements demonstrate that Sr can gradually reduce electrical resistivity while the electron concentration remains almost unchanged at high temperatures. For the films with semiconducting behavior, the charge transport model transforms from variable range hopping to small polaron hopping as the measurement temperature increases. The metalic conductive behaviors in the films with Sr=0.30, 0.40 conform to thermal phonon scattering mode. The difference in charge transport behavior dependent on the A-site cation doping, is clarified. It is revealed that the increasing of phonon energy by Sr doping is responsible for lower activation energy of small polaron hopping, higher carrier mobility, and lower electrical resistivity. Interestingly, the piezoelectric force microscopy (PFM) results demonstrate that all the BSLTO films can exhibit ferroelectricity, especially for the room temperature metallic conduction film with Sr=0.40. These results imply that Sr-doping could be a potential way to explore ferroelectric metal materials for other perovskite oxides.

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Effect of spatially nonlocal versus local optical response of a gold nanorod on modification of the spontaneous emission Sha-Sha Wen(文莎莎), Meng Tian(田锰), Hong Yang(杨红), Su-Jun Xie(谢素君), Xiao-Yun Wang(王小云), Yun Li(李芸), Jie Liu(刘杰), Jin-Zhang Peng(彭金璋), Ke Deng(邓科), He-Ping Zhao(赵鹤平), and Yong-Gang Huang(黄勇刚) Chin. Phys. B, 2021, 30 (2):  027801.  DOI: 10.1088/1674-1056/abc238 Abstract ( 480 )   HTML ( 0 )   PDF (909KB) ( 132 )   The spontaneous emission rate of a two-level quantum emitter (QE) near a gold nanorod is numerically investigated. Three different optical response models for the free-electron gas are adopted, including the classical Drude local response approximation, the nonlocal hydrodynamic model, and the generalized nonlocal optical response model. Nonlocal optical response leads to a blueshift and a reduction in the enhancement of the spontaneous emission rate. Within all the three models, the resonance frequency is largely determined by the aspect ratio (the ratio of the nanorod length to the radius) and increases sharply with decreasing aspect ratio. For nanorod with a fixed length, it is found that the larger the radius is, the higher the resonance frequency is, and the smaller the enhancement is. However, if the length of the nanorod increases, the peak frequency falls sharply, while the spontaneous emission enhancement grows rapidly. For nanorod with a fixed aspect ratio, the peak frequency decreases slowly with increasing nanorod size. Larger nanorod shows smaller nonlocal effect. At a certain frequency, there is an optimal size to maximize the enhancement of the spontaneous emission rate. Higher order modes are more affected by the nonlocal smearing of the induced charges, leading to larger blueshift and greater reduction in the enhancement. These results should be significant for investigating the spontaneous emission rate of a QE around a gold nanorod.

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Investigation of fluorescence resonance energy transfer ultrafast dynamics in electrostatically repulsed and attracted exciton-plasmon systems Hong-Yu Tu(屠宏宇), Ji-Chao Cheng(程基超), Gen-Cai Pan(潘根才), Lu Han(韩露), Bin Duan(段彬), Hai-Yu Wang(王海宇), Qi-Dai Chen(陈岐岱), Shu-Ping Xu(徐抒平), Zhen-Wen Dai(戴振文), and Ling-Yun Pan(潘凌云) Chin. Phys. B, 2021, 30 (2):  027802.  DOI: 10.1088/1674-1056/abb802 Abstract ( 484 )   HTML ( 1 )   PDF (1300KB) ( 73 )   Following the gradual maturation of synthetic techniques for nanomaterials, exciton-plasmon composites have become a research hot-spot due to their controllable energy transfer through electromagnetic fields on the nanoscale. However, most reports ignore fluorescence resonance energy transfer (FRET) under electrostatic repulsion conditions. In this study, the FRET process is investigated in both electrostatic attraction and electrostatic repulsion systems. By changing the Au:quantum dot ratio, local-field induced FRET can be observed with a lifetime of ns and a fast component of hundreds of ps. These results indicate that the intrinsic transfer process can only elucidated by considering both steady and transient state information.

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Modulation of the second-harmonic generation in MoS2 by graphene covering Hot! Chunchun Wu(吴春春), Nianze Shang(尚念泽), Zixun Zhao(赵子荀), Zhihong Zhang(张智宏), Jing Liang(梁晶), Chang Liu(刘畅), Yonggang Zuo(左勇刚), Mingchao Ding(丁铭超), Jinhuan Wang(王金焕), Hao Hong(洪浩), Jie Xiong(熊杰), and Kaihui Liu(刘开辉) Chin. Phys. B, 2021, 30 (2):  027803.  DOI: 10.1088/1674-1056/abd77f Abstract ( 787 )   HTML ( 10 )   PDF (864KB) ( 668 )   Nonlinear optical frequency mixing, which describes new frequencies generation by exciting nonlinear materials with intense light field, has drawn vast interests in the field of photonic devices, material characterization, and optical imaging. Investigating and manipulating the nonlinear optical response of target materials lead us to reveal hidden physics and develop applications in optical devices. Here, we report the realization of facile manipulation of nonlinear optical responses in the example system of MoS2 monolayer by van der Waals interfacial engineering. We found that, the interfacing of monolayer graphene will weaken the exciton oscillator strength in MoS2 monolayer and correspondingly suppress the second harmonic generation (SHG) intensity to 30% under band-gap resonance excitation. While with off-resonance excitation, the SHG intensity would enhance up to 130%, which is conjectured to be induced by the interlayer excitation between MoS2 and graphene. Our investigation provides an effective method for controlling nonlinear optical properties of two-dimensional materials and therefore facilitates their future applications in optoelectronic and photonic devices.

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Influence of an inserted bar on the flow regimes in the hopper Yi Peng(彭毅), Sheng Zhang(张晟), Mengke Wang(王梦柯), Guanghui Yang(杨光辉), Jiangfeng Wan(万江锋), Liangwen Chen(陈良文), and Lei Yang(杨磊) Chin. Phys. B, 2021, 30 (2):  028101.  DOI: 10.1088/1674-1056/abcf40 Abstract ( 426 )   HTML ( 0 )   PDF (696KB) ( 198 )   We investigated the influence of an inserted bar on the hopper flow experimentally. Three geometrical parameters, size of upper outlet D1, size of lower outlet D0, and the height of bar H, are variables here. With varying H we found three regimes: one transition from clogging to a surface flow and another transition from a surface flow to a dense flow. For the dense flow, the flow rate follows Beverloo's law and there is a saturation of inclination of free surface θ . We plotted the velocity field and there is a uniform linear relation between the particle velocity and depth from the free surface. We also found that the required value of D1 to guarantee the connectivity of flow is little smaller than D0. For the transition from a surface flow to a dense flow, there is a jump of flow rate and the minimum θ for flowing is two degrees larger than the repose angle.

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Molecular beam epitaxy growth of iodide thin films Xinqiang Cai(蔡新强), Zhilin Xu(徐智临), Shuai-Hua Ji(季帅华), Na Li(李娜), and Xi Chen(陈曦) Chin. Phys. B, 2021, 30 (2):  028102.  DOI: 10.1088/1674-1056/abcf93 Abstract ( 596 )   HTML ( 3 )   PDF (1116KB) ( 485 )   Study of two-dimensional (2D) magnetic materials is important for both fundamental research and application. Here we report molecular beam epitaxy growth of iodides, candidates for exhibiting 2D magnetism. Decomposition of CrI3 is utilized to produce stable gaseous I2 flux. Growth of MnI2, GdI3, and CrI2 down to monolayer is successful achieved by co-depositing I2 and corresponding metal atoms. The thin films of the three materials are characterized by scanning tunneling microscope and found to be insulators with bandgaps of 4.4 eV, 0.6 eV, and 3.0 eV, respectively. The film growth paves the way for further study of magnetic properties at the 2D limit.

INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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Effects of heat transfer in a growing particle layer on microstructural evolution during solidification of colloidal suspensions Jia-Xue You(游家学), Yun-Han Zhang(张运涵), Zhi-Jun Wang(王志军), Jin-Cheng Wang(王锦程), and Sheng-Zhong Liu(刘生忠) Chin. Phys. B, 2021, 30 (2):  028103.  DOI: 10.1088/1674-1056/abc168 Abstract ( 404 )   HTML ( 0 )   PDF (1516KB) ( 111 )   Heat transfer is the foundation of freezing colloidal suspensions and a key factor for the interface movement. However, how the thermal conductivity of particles affects freezing microstructural evolution remains unknown. Here in this work, a mathematical model is built up to investigate thermal interactions among a growing particle layer, pulling speeds, and the freezing interface under a thermal gradient. Experiments are conducted to confirm the tendency predictions of the model. With the increase of pulling speeds, the drifting distance of the freezing interface increases and the time to finish drifting decreases. When the thermal conductivity of particles (k p) is smaller than that of the surrounding (k w), the freezing interface tends to go forward to the warm side. Contrarily, the freezing interface tends to go back to the cold side when the thermal conductivity of particles is larger than that of the surrounding (α =k p/k w >1). It originates from the shape of the local freezing interface: convex (α <1) or concave (α >1). These morphological changes in the local interface modify the premelting drag force F f. When α <1, F f decreases and the freezing morphology tends to be the frozen fringe. When α >1, F f increases and the freezing morphologies tend to be ice spears. These understandings of how the thermal conductivity of particles affect microstructural evolution may optimize the production of freeze-casting materials and their structural-functional properties.

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Mechanism of titanium-nitride chemical mechanical polishing Dao-Huan Feng(冯道欢), Ruo-Bing Wang(王若冰), Ao-Xue Xu(徐傲雪), Fan Xu(徐帆), Wei-Lei Wang(汪为磊), Wei-Li Liu(刘卫丽), and Zhi-Tang Song(宋志棠) Chin. Phys. B, 2021, 30 (2):  028301.  DOI: 10.1088/1674-1056/abc161 Abstract ( 657 )   HTML ( 3 )   PDF (1738KB) ( 380 )   During the preparation of the phase change memory, the deposition and chemical mechanical polishing (CMP) of titanium nitride (TiN) are indispensable. A new acidic slurry added with sodium hypochlorite (NaClO) as an oxidizer is developed for the CMP of TiN film. It has achieved a material removal rate of 76 nm/min, a high selectivity between TiN film and silica (SiO2) films of 128:1, a selectivity between TiN film and tungsten film of 84:1 and a high surface quality. To understand the mechanism of TiN CMP process, x-ray photoelectron (XPS) spectroscope and potentiodynamic polarization measurement are performed. It is found that the mechanism of TiN CMP process is cyclic reaction polishing mechanism. In addition, both static corrosion rate and the inductively coupled plasma results indicate TiN would not be dissolved, which means that the mechanical removal process of oxide layer plays a decisive role in the material removal rate. Finally, the mechanism of TiN polishing process is given based on the analysis of surface potential and the description of blocking function.

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Snapback-free shorted anode LIGBT with controlled anode barrier and resistance Shun Li(李顺), Jin-Sha Zhang(张金沙), Wei-Zhong Chen(陈伟中), Yao Huang(黄垚), Li-Jun He(贺利军), and Yi Huang(黄义) Chin. Phys. B, 2021, 30 (2):  028501.  DOI: 10.1088/1674-1056/abb7fc Abstract ( 445 )   HTML ( 1 )   PDF (871KB) ( 129 )   A novel shorted anode lateral-insulated gate bipolar transistor (SA LIGBT) with snapback-free characteristic is proposed and investigated. The device features a controlled barrier V barrier and resistance R SA in anode, named CBR LIGBT. The electron barrier is formed by the P-float/N-buffer junction, while the anode resistance includes the polysilicon layer and N-float. At forward conduction stage, the V barrier and R SA can be increased by adjusting the doping of the P-float and polysilicon layer, respectively, which can suppress the unipolar mode to eliminate the snapback. At turn-off stage, the low-resistance extraction path (N-buffer/P-float/polysilicon layer /N-float) can quickly extract the electrons in the N-drift, which can effectively accelerate the turn-off speed of the device. The simulation results show that at the same V on of 1.3 V, the E off of the CBR LIGBT is reduced by 85%, 73%, and 59.6% compared with the SSA LIGBT, conventional LIGBT, and TSA LIGBT, respectively. Additionally, at the same E off of 1.5 mJ/cm2, the CBR LIGBT achieves the lowest V on of 1.1 V compared with the other LIGBTs.

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Performance analysis of GaN-based high-electron-mobility transistors with postpassivation plasma treatment Xing-Ye Zhou(周幸叶), Xin Tan(谭鑫), Yuan-Jie Lv(吕元杰), Guo-Dong Gu(顾国栋), Zhi-Rong Zhang(张志荣), Yan-Min Guo(郭艳敏), Zhi-Hong Feng(冯志红), and Shu-Jun Cai(蔡树军) Chin. Phys. B, 2021, 30 (2):  028502.  DOI: 10.1088/1674-1056/abb7f6 Abstract ( 610 )   HTML ( 2 )   PDF (657KB) ( 101 )   AlGaN/GaN high-electron-mobility transistors (HEMTs) with postpassivation plasma treatment are demonstrated and investigated for the first time. The results show that postpassivation plasma treatment can reduce the gate leakage and enhance the drain current. Comparing with the conventional devices, the gate leakage of AlGaN/GaN HEMTs with postpassivation plasma decreases greatly while the drain current increases. Capacitance-voltage measurement and frequency-dependent conductance method are used to study the surface and interface traps. The mechanism analysis indicates that the surface traps in the access region can be reduced by postpassivation plasma treatment and thus suppress the effect of virtual gate, which can explain the improvement of DC characteristics of devices. Moreover, the density and time constant of interface traps under the gate are extracted and analyzed.

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Lateral depletion-mode 4H-SiC n-channel junction field-effect transistors operational at 400 °C Si-Cheng Liu(刘思成), Xiao-Yan Tang(汤晓燕), Qing-Wen Song(宋庆文), Hao Yuan(袁昊), Yi-Meng Zhang(张艺蒙), Yi-Men Zhang(张义门), and Yu-Ming Zhang(张玉明) Chin. Phys. B, 2021, 30 (2):  028503.  DOI: 10.1088/1674-1056/abc0df Abstract ( 426 )   HTML ( 0 )   PDF (876KB) ( 94 )   This paper presents the development of lateral depletion-mode n-channel 4H-SiC junction field-effect transistors (LJFETs) using double-mesa process toward high-temperature integrated circuit (IC) applications. At room temperature, the fabricated LJFETs show a drain-to-source saturation current of 23.03 μ A/μm, which corresponds to a current density of 7678 A/cm2. The gate-to-source parasitic resistance of 17.56 kΩ μ m is reduced to contribute only 13.49% of the on-resistance of 130.15 kΩ μ m, which helps to improve the transconductance up to 8.61 μ S/μm. High temperature characteristics of LJFETs were performed from room temperature to 400 °C. At temperatures up to 400 °C in air, it is observed that the fabricated LJFETs still show normally-on operating characteristics. The drain-to-source saturation current, transconductance and intrinsic gain at 400 °C are 7.47 μ A/μm, 2.35 μ S/μm and 41.35, respectively. These results show significant improvement over state-of-the-art and make them attractive for high-temperature IC applications.

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Growth of high quality InSb thin films on GaAs substrates by molecular beam epitaxy method with AlInSb/GaSb as compound buffer layers Yong Li(李勇), Xiao-Ming Li(李晓明), Rui-Ting Hao(郝瑞亭), Jie Guo(郭杰), Yu Zhuang(庄玉), Su-Ning Cui(崔素宁), Guo-Shuai Wei(魏国帅), Xiao-Le Ma(马晓乐), Guo-Wei Wang(王国伟), Ying-Qiang Xu(徐应强), Zhi-Chuan Niu(牛智川), and Yao Wang(王耀) Chin. Phys. B, 2021, 30 (2):  028504.  DOI: 10.1088/1674-1056/abc152 Abstract ( 732 )   HTML ( 5 )   PDF (3217KB) ( 174 )   A series of InSb thin films were grown on GaAs substrates by molecular beam epitaxy (MBE). GaSb/AlInSb is used as a compound buffer layer to release the strain caused by the lattice mismatch between the substrate and the epitaxial layer, so as to reduce the system defects. At the same time, the influence of different interface structures of AlInSb on the surface morphology of buffer layer is explored. The propagation mechanism of defects with the growth of buffer layer is compared and analyzed. The relationship between the quality of InSb thin films and the structure of buffer layer is summarized. Finally, the growth of high quality InSb thin films is realized.

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Microstructure, optical, and photoluminescence properties of β -Ga2O3 films prepared by pulsed laser deposition under different oxygen partial pressures Rui-Rui Cui(崔瑞瑞), Jun Zhang(张俊), Zi-Jiang Luo(罗子江), Xiang Guo(郭祥), Zhao Ding(丁召), and Chao-Yong Deng(邓朝勇) Chin. Phys. B, 2021, 30 (2):  028505.  DOI: 10.1088/1674-1056/abc164 Abstract ( 407 )   HTML ( 0 )   PDF (1704KB) ( 284 )   The β -Ga2O3 films are prepared on polished Al2O3 (0001) substrates by pulsed laser deposition at different oxygen partial pressures. The influence of oxygen partial pressure on crystal structure, surface morphology, thickness, optical properties, and photoluminescence properties are studied by x-ray diffraction (XRD), atomic force microscope (AFM), scanning electron microscope (SEM), spectrophotometer, and spectrofluorometer. The results of x-ray diffraction and atomic force microscope indicate that with the decrease of oxygen pressure, the full width at half maximum (FWHM) and grain size increase. With the increase of oxygen pressure, the thickness of the films first increases and then decreases. The room-temperature UV-visible (UV-Vis) absorption spectra show that the bandgap of the β -Ga2O3 film increases from 4.76 eV to 4.91 eV as oxygen pressure decreasing. Room temperature photoluminescence spectra reveal that the emission band can be divided into four Gaussian bands centered at about 310 nm (∼ 4.0 eV), 360 nm (∼ 3.44 eV), 445 nm (∼ 2.79 eV), and 467 nm (∼ 2.66 eV), respectively. In addition, the total photoluminescence intensity decreases with oxygen pressure increasing, and it is found that the two UV bands are related to self-trapped holes (STHs) at O1 sites and between two O2-s sites, respectively, and the two blue bands originate from V Ga 2- at Ga1 tetrahedral sites. The photoluminescence mechanism of the films is also discussed. These results will lay a foundation for investigating the Ga2O3 film-based electronic devices.

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RF magnetron sputtering induced the perpendicular magnetic anisotropy modification in Pt/Co based multilayers Runze Li(李润泽), Yucai Li(李予才), Yu Sheng(盛宇), and Kaiyou Wang(王开友) Chin. Phys. B, 2021, 30 (2):  028506.  DOI: 10.1088/1674-1056/abcf9d Abstract ( 569 )   HTML ( 3 )   PDF (674KB) ( 258 )   We demonstrate that radio frequency (RF) magnetron sputtering technique can modify the perpendicular magnetic anisotropy (PMA) of Pt/Co/normal metal (NM) thin films. Influence of ion irradiation during RF magnetron sputtering should not be neglected and it can weaken PMA of the deposited magnetic films. The magnitude of this influence can be controlled by tuning RF magnetron sputtering deposition conditions and the upper NM layer thickness. According to the stopping and range of ions in matter (SRIM) simulation results, defects such as displacement atoms and vacancies in the deposited film will increase after the RF magnetron sputtering, which can account for the weakness of PMA. The amplitude changes of the Hall resistance and the threshold current intensity of spin orbit torque (SOT) induced magnetization switching also can be modified. Our study could be useful for controlling magnetic properties of PMA films and designing new type of SOT-based spintronic devices.

REVIEW

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Negative photoconductivity in low-dimensional materials Boyao Cui(崔博垚), Yanhui Xing(邢艳辉), Jun Han(韩军), Weiming Lv(吕伟明), Wenxing Lv(吕文星), Ting Lei(雷挺), Yao Zhang(张尧), Haixin Ma(马海鑫), Zhongming Zeng(曾中明), and Baoshun Zhang(张宝顺) Chin. Phys. B, 2021, 30 (2):  028507.  DOI: 10.1088/1674-1056/abcf41 Abstract ( 499 )   HTML ( 10 )   PDF (1867KB) ( 606 )   In recent years, low-dimensional materials have received extensive attention in the field of electronics and optoelectronics. Among them, photoelectric devices based on photoconductive effect in low-dimensional materials have a broad development space. In contrast to positive photoconductivity, negative photoconductivity (NPC) refers to a phenomenon that the conductivity decreases under illumination. It has novel application prospects in the field of optoelectronics, memory, and gas detection, etc. In this paper, we review reports about the NPC effect in low-dimensional materials and systematically summarize the mechanisms to form the NPC effect in existing low-dimensional materials.

INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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An electromagnetic view of relay time in propagation of neural signals Jing-Jing Xu(徐晶晶), San-Jin Xu(徐三津), Fan Wang(王帆), and Sheng-Yong Xu(许胜勇) Chin. Phys. B, 2021, 30 (2):  028701.  DOI: 10.1088/1674-1056/abc0d2 Abstract ( 359 )   HTML ( 3 )   PDF (906KB) ( 86 )   We review the experimental and computational data about the propagation of neural signals in myelinated axons in mice, cats, rabbits, and frogs published in the past five decades. In contrast to the natural assumption that neural signals occur one by one in time and in space, we figure out that neural signals are highly overlapped in time between neighboring nodes. This phenomenon was occasionally illustrated in some early reports, but seemed to have been overlooked for some time. The shift in time between two successive neural signals from neighboring nodes, defined as relay time τ , was calculated to be only 16.3 μ s-87.0 μ s, i.e., 0.8%-4.4% of the average duration of an action potential peak (roughly 2 ms). We present a clearer picture of the exact physical process about how the information transmits along a myelinated axon, rather than a whole action potential peak, what is transmitted is only a rising electric field caused by transmembrane ion flows. Here in the paper, τ represents the waiting time until the neighboring node senses an attenuated electric field reaching the threshold to trigger the open state. The mechanisms addressed in this work have the potential to be universal, and may hold clues to revealing the exact triggering processes of voltage-gated ion channels and various brain functions.

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Quantitative coherence analysis of dual phase grating x-ray interferometry with source grating Zhi-Li Wang(王志立), Rui-Cheng Zhou(周瑞成), Li-Ming Zhao(赵立明), Kun Ren(任坤), Wen Xu(徐文), Bo Liu(刘波), and Heng Chen(陈恒) Chin. Phys. B, 2021, 30 (2):  028702.  DOI: 10.1088/1674-1056/abb7fd Abstract ( 436 )   HTML ( 3 )   PDF (562KB) ( 208 )   Dual phase grating x-ray interferometry is compatible with common imaging detectors, and abandons the use of an absorption analyzer grating to reduce the radiation dose. When using x-ray tubes, an absorbing source grating must be introduced into the dual phase grating interferometer. In order to attain a high fringe visibility, in this work we conduct a quantitative coherence analysis of dual phase grating interferometry to find how the source grating affects the fringe visibility. Theoretical analysis shows that with the generalized Lau condition satisfied, the fringe visibility is influenced by the duty cycle of the source grating and the transmission through the grating bar. And the influence of the source grating profile on the fringe visibility is independent of the phase grating type. Numerical results illustrate that the maximum achievable fringe visibility decreases significantly with increasing transmission in the grating bar. Under a given transmission, one can always find an optimal duty cycle to maximize the fringe visibility. These results can be used as general guidelines for designing and optimizing dual phase grating x-ray interferometers for potential applications.

SPECIAL TOPIC—Modeling and simulations for the structures and functions of proteins and nucleic acids

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Folding nucleus and unfolding dynamics of protein 2GB1 Xuefeng Wei(韦学锋) and Yanting Wang(王延颋) Chin. Phys. B, 2021, 30 (2):  028703.  DOI: 10.1088/1674-1056/abbbfa Abstract ( 0 )   HTML ( 0 )   PDF (874KB) ( 177 )   The folding of many small proteins is kinetically a two-state process with one major free-energy barrier to overcome, which can be roughly regarded as the inverse process of unfolding. In this work, we first use a Gaussian network model to predict the folding nucleus corresponding to the major free-energy barrier of protein 2GB1, and find that the folding nucleus is located in the β -sheet domain. High-temperature molecular dynamics simulations are then used to investigate the unfolding process of 2GB1. We draw free-energy surface from unfolding simulations, taking RMSD and contact number as reaction coordinates, which confirms that the folding of 2GB1 is kinetically a two-state process. The comparison of the contact maps before and after the free energy barrier indicates that the transition from native to non-native structure of the protein is kinetically caused by the destruction of the β -sheet domain, which manifests that the folding nucleus is indeed located in the β -sheet domain. Moreover, the constrained MD simulation further confirms that the destruction of the secondary structures does not alter the topology of the protein retained by the folding nucleus. These results provide vital information for upcoming researchers to further understand protein folding in similar systems.

INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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Identification of denatured and normal biological tissues based on compressed sensing and refined composite multi-scale fuzzy entropy during high intensity focused ultrasound treatment Shang-Qu Yan(颜上取), Han Zhang(张含), Bei Liu(刘备), Hao Tang(汤昊), and Sheng-You Qian(钱盛友) Chin. Phys. B, 2021, 30 (2):  028704.  DOI: 10.1088/1674-1056/abcfa7 Abstract ( 435 )   HTML ( 0 )   PDF (887KB) ( 109 )   In high intensity focused ultrasound (HIFU) treatment, it is crucial to accurately identify denatured and normal biological tissues. In this paper, a novel method based on compressed sensing (CS) and refined composite multi-scale fuzzy entropy (RCMFE) is proposed. First, CS is used to denoise the HIFU echo signals. Then the multi-scale fuzzy entropy (MFE) and RCMFE of the denoised HIFU echo signals are calculated. This study analyzed 90 cases of HIFU echo signals, including 45 cases in normal status and 45 cases in denatured status, and the results show that although both MFE and RCMFE can be used to identify denatured tissues, the intra-class distance of RCMFE on each scale factor is smaller than MFE, and the inter-class distance is larger than MFE. Compared with MFE, RCMFE can calculate the complexity of the signal more accurately and improve the stability, compactness, and separability. When RCMFE is selected as the characteristic parameter, the RCMFE difference between denatured and normal biological tissues is more evident than that of MFE, which helps doctors evaluate the treatment effect more accurately. When the scale factor is selected as 16, the best distinguishing effect can be obtained.

TOPICAL REVIEW—Modeling and simulations for the structures and functions of proteins and nucleic acids

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Statistical potentials for 3D structure evaluation: From proteins to RNAs Ya-Lan Tan(谭雅岚), Chen-Jie Feng(封晨洁), Xunxun Wang(王勋勋), Wenbing Zhang(张文炳), and Zhi-Jie Tan(谭志杰) Chin. Phys. B, 2021, 30 (2):  028705.  DOI: 10.1088/1674-1056/abc0d6 Abstract ( 0 )   HTML ( 0 )   PDF (752KB) ( 267 )   Structure evaluation is critical to in silico 3-dimensional structure predictions for biomacromolecules such as proteins and RNAs. For proteins, structure evaluation has been paid attention over three decades along with protein folding problem, and statistical potentials have been shown to be effective and efficient in protein structure prediction and evaluation. In recent two decades, RNA folding problem has attracted much attention and several statistical potentials have been developed for RNA structure evaluation, partially with the aid of the progress in protein structure prediction. In this review, we will firstly give a brief overview on the existing statistical potentials for protein structure evaluation. Afterwards, we will introduce the recently developed statistical potentials for RNA structure evaluation. Finally, we will emphasize the perspective on developing new statistical potentials for RNAs in the near future.