Table of contents

05 May 2020, Volume 29 Issue 5 Previous issue    Next issue

GENERAL

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Two integrable generalizations of WKI and FL equations: Positive and negative flows, and conservation laws Xian-Guo Geng(耿献国), Fei-Ying Guo(郭飞英), Yun-Yun Zhai(翟云云) Chin. Phys. B, 2020, 29 (5):  050201.  DOI: 10.1088/1674-1056/ab7e9d Abstract ( 628 )   HTML   PDF (468KB) ( 236 )   With the aid of Lenard recursion equations, an integrable hierarchy of nonlinear evolution equations associated with a 2×2 matrix spectral problem is proposed, in which the first nontrivial member in the positive flows can be reduced to a new generalization of the Wadati-Konno-Ichikawa (WKI) equation. Further, a new generalization of the Fokas-Lenells (FL) equation is derived from the negative flows. Resorting to these two Lax pairs and Riccati-type equations, the infinite conservation laws of these two corresponding equations are obtained.

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Generation of tripartite Einstein-Podolsky-Rosen steering by cascaded nonlinear process Yu Liu(刘瑜), Su-Ling Liang(梁素玲), Guang-Ri Jin(金光日), You-Bin Yu(俞友宾), Jian-Yu Lan(蓝建宇), Xiao-Bin He(何小斌), Kang-Xian Guo(郭康贤) Chin. Phys. B, 2020, 29 (5):  050301.  DOI: 10.1088/1674-1056/ab7da6 Abstract ( 760 )   HTML   PDF (614KB) ( 196 )   A scheme is proposed to generate genuine tripartite Einstein-Podolsky-Rosen (EPR) steering in cascaded nonlinear process of the fourth-harmonic generation. The second-harmonic is generated by the first double-frequency process in an optical superlattice. Then, the fourth-harmonic is produced by the second cascaded double-frequency process through quasi-phase-matching technique in the same optical superlattice. The genuine tripartite EPR steering among the pump, the second-harmonic, and the fourth-harmonic beams can be obtained by this cascaded nonlinear process according to a criterion for genuine multipartite quantum steering. The quantum steering properties are discussed by adjusting the parameters related to the cascaded nonlinear system. The present research provides a reference scheme and data for obtaining good multipartite EPR steering in experiment and can advance the applications of quantum steering in the quantum information processing.

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Margolus-Levitin speed limit across quantum to classical regimes based on trace distance Shao-Xiong Wu(武少雄), Chang-Shui Yu(于长水) Chin. Phys. B, 2020, 29 (5):  050302.  DOI: 10.1088/1674-1056/ab7dab Abstract ( 619 )   HTML   PDF (483KB) ( 145 )   The classical version of Mandelstam-Tamm speed limit based on the Wigner function in phase space was reported by Shanahan et al. [Phys. Rev. Lett. 120 070401 (2018)]. We present the Margolus-Levitin speed limit across the quantum-to-classical transition in phase space based on the trace distance. The Margolus-Levitin speed limit is set by the Schatten L1 norm of the generator of time-dependent evolution for both the quantum and classical domains. As an example, the time-dependent harmonic oscillator is considered to illustrate the result.

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Recast combination functions of coordinate and momentum operators into their ordered product forms Lei Wang(王磊), Xiang-Guo Meng(孟祥国), Ji-Suo Wang(王继锁) Chin. Phys. B, 2020, 29 (5):  050303.  DOI: 10.1088/1674-1056/ab7dbd Abstract ( 553 )   HTML   PDF (495KB) ( 120 )   By using the parameter differential method of operators, we recast the combination function of coordinate and momentum operators into its normal and anti-normal orderings, which is more ecumenical, simpler, and neater than the existing ways. These products are very useful in obtaining some new differential relations and useful mathematical integral formulas. Further, we derive the normally ordered form of the operator (fQ+gP)-n with n being an arbitrary positive integer by using the parameter tracing method of operators together with the intermediate coordinate-momentum representation. In addition, general mutual transformation rules of the normal and anti-normal orderings, which have good universality, are derived and hence the anti-normal ordering of (fQ+gP)-n is also obtained. Finally, the application of some new identities is given.

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Qubit movement-assisted entanglement swapping Sare Golkar, Mohammad Kazem Tavassoly, Alireza Nourmandipour Chin. Phys. B, 2020, 29 (5):  050304.  DOI: 10.1088/1674-1056/ab7da3 Abstract ( 640 )   HTML   PDF (1058KB) ( 99 )   We propose a scheme to generate entanglement between two distant qubits (two-level atom) which are separately trapped in their own (in general) non-Markovian dissipative cavities by utilizing entangling swapping, considering the case in which the qubits can move along their cavity axes rather than a static state of motion. We first examine the role of movement of the qubit by studying the entropy evolution for each subsystem. The average entropy over the initial states of the qubit is calculated. Then by performing a Bell state measurement on the fields leaving the cavities, we swap the entanglement between qubit-field in each cavity into qubit-qubit and field-field subsystems. The entangling power is used to measure the average amount of swapped entanglement over all possible pure initial states. Our results are presented in two weak and strong coupling regimes, illustrating the positive role of movement of the qubits on the swapped entanglement. It is revealed that by considering certain conditions for the initial state of qubits, it is possible to achieve a maximally long-leaving stationary entanglement (Bell state) which is entirely independent of the environmental variables as well as the velocity of qubits. This happens when the two qubits have the same velocities.

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Quantum legitimacy of reversible gate and a new design of multiplier based on R gate Tingyu Ge(葛庭宇), Tinggui Zhang(张廷桂), Xiaofen Huang(黄晓芬) Chin. Phys. B, 2020, 29 (5):  050305.  DOI: 10.1088/1674-1056/ab7d9d Abstract ( 684 )   HTML   PDF (544KB) ( 140 )   Quantum full adders play a key role in the design of quantum computers. The efficiency of a quantum adder directly determines the speed of the quantum computer, and its complexity is closely related to the difficulty and the cost of building a quantum computer. The existed full adder based on R gate is a great design but it is not suitable to construct a quantum multiplier. We show the quantum legitimacy of some common reversible gates, then use R gate to propose a new design of a quantum full adder. We utilize the new designed quantum full adder to optimize the quantum multiplier which is based on R gate. It is shown that the new designed one can be optimized by a local optimization rule so that it will have lower quantum cost than before.

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Fast achievement of quantum state transfer and distributed quantum entanglement by dressed states Hot! Liang Tian(田亮), Li-Li Sun(孙立莉), Xiao-Yu Zhu(朱小瑜), Xue-Ke Song(宋学科), Lei-Lei Yan(闫磊磊), Er-Jun Liang(梁二军), Shi-Lei Su(苏石磊), Mang Feng(冯芒) Chin. Phys. B, 2020, 29 (5):  050306.  DOI: 10.1088/1674-1056/ab7e9a Abstract ( 926 )   HTML   PDF (1939KB) ( 512 )   We propose schemes to realize quantum state transfer and prepare quantum entanglement in coupled cavity and cavity-fiber-cavity systems, respectively, by using the dressed state method. We first give the expression of pulses shape by using dressed states and then find a group of Gaussian pulses that are easy to realize in experiment to replace the ideal pulses by curve fitting. We also study the influence of some parameters fluctuation, atomic spontaneous emission, and photon leakage on fidelity. The results show that our schemes have good robustness. Because the atoms are trapped in different cavities, it is easy to perform different operations on different atoms. The proposed schemes have the potential applications in dressed states for distributed quantum information processing tasks.

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Experimental demonstration of tight duality relation inthree-path interferometer Zhi-Jin Ke(柯芝锦), Yu Meng(孟雨), Yi-Tao Wang(王轶韬), Shang Yu(俞上), Wei Liu(刘伟), Zhi-Peng Li(李志鹏), Hang Wang(汪航), Qiang Li(李强), Jin-Shi Xu(许金时), Jian-Shun Tang(唐建顺), Chuan-Feng Li(李传锋), Guang-Can Guo(郭光灿) Chin. Phys. B, 2020, 29 (5):  050307.  DOI: 10.1088/1674-1056/ab7ea2 Abstract ( 742 )   HTML   PDF (735KB) ( 169 )   Bohr's principle of complementarity has a long history and it is an important topic in quantum theory, among which the famous example is the duality relation. The relation between visibility C and distinguishability D, C2 + D2 ≤1, has long been recognized as the only representative of the duality relation. However, recent researches have shown that this inequality is not good enough because it is not tight for multipath interferometers. Meanwhile, a tight bound for the multipath interferometer has been put forward. Here we design and experimentally implement a three-path interferometer coupling with path indicator states. The wave property of photons is characterized by l1-norm coherence measure, and the particle property is based on distinguishability of the indicator states. The new duality relation of the three-path interferometer is demonstrated in our experiment, which bounds the union of a right triangle and a part of elliptical area inside the quadrant of a unit circle. Data analysis confirms that the new bound is tight for photons in three-path interferometers.

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Phase-modulated quadrature squeezing in two coupled cavities containing a two-level system Hao-Zhen Li(李浩珍), Ran Zeng(曾然), Xue-Fang Zhou(周雪芳), Mei-Hua Bi(毕美华), Jing-Ping Xu(许静平), Ya-Ping Yang(羊亚平) Chin. Phys. B, 2020, 29 (5):  050308.  DOI: 10.1088/1674-1056/ab820a Abstract ( 656 )   HTML   PDF (787KB) ( 255 )   The phase-modulated quadrature squeezing in the system that composed of two coupled cavities interacting with a two-level atom is investigated. The variances of the amplitude and phase quadrature of the output field are calculated. It turns out that the squeezing behaviors of the output field can be obviously modified due to the phase difference of the coupling strengths between the atom and the two cavities. The squeezing in one quadrature (i.e., phase quadrature) can be transferred into another (i.e., amplitude quadrature), or the quadrature squeezing located at the low-frequency region can be transferred into the high-frequency region by modulating the relative phase of the coupling strengths. Furthermore, the effects of the decay mismatch between the two cavities and the coupling mismatch between the atom and the cavities on the quadrature squeezing have been discussed. The results show that both the decay mismatch and the coupling mismatch play a positive role in generating better quadrature squeezing.

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Hybrid linear amplifier-involved detection for continuous variable quantum key distribution with thermal states Yu-Qian He(贺宇千), Yun Mao(毛云), Hai Zhong(钟海), Duang Huang(黄端), Ying Guo(郭迎) Chin. Phys. B, 2020, 29 (5):  050309.  DOI: 10.1088/1674-1056/ab8216 Abstract ( 680 )   HTML   PDF (2317KB) ( 169 )   Continuous-variable quantum key distribution (CVQKD) can be integrated with thermal states for short-distance wireless quantum communications. However, its performance is usually restricted with the practical thermal noise. We propose a method to improve the security threshold of thermal-state (TS) CVQKD by employing a heralded hybrid linear amplifier (HLA) at the receiver. We find the effect of thermal noise on the HLA-involved scheme in near-and-mid infrared band or terahertz band for direct and reverse reconciliation. Numerical simulations show that the HLA-involved scheme can compensate for the detriment of thermal noise and hence increase the security threshold of TS-CVQKD. In near-and-mid infrared band, security threshold can be extended by 2.1 dB in channel loss for direct reconciliation and 1.6 dB for reverse reconciliation, whereas in terahertz band, security threshold can be slightly enhanced for the gain parameter less than 1 due to the rise in thermal noise.

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Thermodynamics and weak cosmic censorship conjecture of charged AdS black hole in the Rastall gravity with pressure Xin-Yun Hu(胡馨匀), Ke-Jian He(何柯健), Zhong-Hua Li(李中华), Guo-Ping Li(李国平) Chin. Phys. B, 2020, 29 (5):  050401.  DOI: 10.1088/1674-1056/ab7daa Abstract ( 708 )   HTML   PDF (1385KB) ( 132 )   Treating the cosmological constant as a dynamical variable, we investigate the thermodynamics and weak cosmic censorship conjecture (WCCC) of a charged AdS black hole (BH) in the Rastall gravity. We determine the energy momentum relation of charged fermion at the horizon of the BH using the Dirac equation. Based on this relation, it is shown that the first law of thermodynamics still holds as a fermion is absorbed by the BH. However, the entropy of both the extremal and near-extremal BH decreases in the irreversible process, which means that the second law of thermodynamics is violated. Furthermore, we verify the validity of the WCCC by the minimum values of the metric function h(r) at its final state. For the extremal charged AdS BH in the Rastall gravity, we find that the WCCC is always valid since the BH is extreme. While for the case of near-extremal BH, we find that the WCCC could be violable in the extended phase space (EPS), depending on the value of the parameters of the BH and their variations.

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Quantum fluctuation of entanglement for accelerated two-level detectors Si-Xuan Zhang(张思轩), Tong-Hua Liu(刘统华), Shuo Cao(曹硕), Yu-Ting Liu(刘宇婷), Shuai-Bo Geng(耿率博), Yu-Jie Lian(连禹杰) Chin. Phys. B, 2020, 29 (5):  050402.  DOI: 10.1088/1674-1056/ab7d9a Abstract ( 603 )   HTML   PDF (970KB) ( 98 )   It is well known that the quantum fluctuation of entanglement (QFE) between Unruh-De Witt detector (modeled by a two-level atom) is always investigated in a relativistic setting. However, both of the Unruh radiation and quantum fluctuation effects play an important role in precise measurements of quantum entanglement. In this paper, we have quantitatively analyzed how the relativistic motion affects the QFE for two entangled Unruh-De Witt detectors, one of which is accelerated and interacting with the neighbor external scalar field. Our results show that the QFE, which initially increases by the Unruh thermal noise, will suddenly decay when the acceleration reaches to a considerably large value. Therefore, the relativistic effect will lead to non-negligible QFE effect. We also find that the initial QFE (without acceleration effect) reaches its minimum value at the maximally entangled state and the separable state. More importantly, our analysis demonstrates that although the QFE has a huge decay when the acceleration is greater than ～0.96, the ratio of ΔE/C is still very large, due to the simultaneous decay of concurrence to a very low value. Finally, enlightened by the well-known equivalence principle, we discuss the possibility of applying the above findings to the dynamics of QFE under the influence of gravitation field.

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Asymmetric stochastic resonance under non-Gaussian colored noise and time-delayed feedback Ting-Ting Shi(石婷婷), Xue-Mei Xu(许雪梅), Ke-Hui Sun(孙克辉), Yi-Peng Ding(丁一鹏), Guo-Wei Huang(黄国伟) Chin. Phys. B, 2020, 29 (5):  050501.  DOI: 10.1088/1674-1056/ab7e9f Abstract ( 683 )   HTML   PDF (2900KB) ( 149 )   Based on adiabatic approximation theory, in this paper we study the asymmetric stochastic resonance system with time-delayed feedback driven by non-Gaussian colored noise. The analytical expressions of the mean first-passage time (MFPT) and output signal-to-noise ratio (SNR) are derived by using a path integral approach, unified colored-noise approximation (UCNA), and small delay approximation. The effects of time-delayed feedback and non-Gaussian colored noise on the output SNR are analyzed. Moreover, three types of asymmetric potential function characteristics are thoroughly discussed. And they are well-depth asymmetry (DASR), well-width asymmetry (WASR), and synchronous action of well-depth and well-width asymmetry (DWASR), respectively. The conclusion of this paper is that the time-delayed feedback can suppress SR, however, the non-Gaussian noise deviation parameter has the opposite effect. Moreover, the correlation time plays a significant role in improving SNR, and the SNR of asymmetric stochastic resonance is higher than that of symmetric stochastic resonance. Our experiments demonstrate that the appropriate parameters can make the asymmetric stochastic resonance perform better to detect weak signals than the symmetric stochastic resonance, in which no matter whether these signals have low frequency or high frequency, accompanied by strong or weak noise.

SPECIAL TOPIC—Topological 2D materials

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Topological Anderson insulator in two-dimensional non-Hermitian systems Hongfang Liu(刘宏芳), Zixian Su(苏子贤), Zhi-Qiang Zhang(张智强), Hua Jiang(江华) Chin. Phys. B, 2020, 29 (5):  050502.  DOI: 10.1088/1674-1056/ab8201 Abstract ( 1182 )   HTML   PDF (1891KB) ( 392 )   We study the disorder-induced phase transition in two-dimensional non-Hermitian systems. First, the applicability of the noncommutative geometric method (NGM) in non-Hermitian systems is examined. By calculating the Chern number of two different systems (a square sample and a cylindrical one), the numerical results calculated by NGM are compared with the analytical one, and the phase boundary obtained by NGM is found to be in good agreement with the theoretical prediction. Then, we use NGM to investigate the evolution of the Chern number in non-Hermitian samples with the disorder effect. For the square sample, the stability of the non-Hermitian Chern insulator under disorder is confirmed. Significantly, we obtain a nontrivial topological phase induced by disorder. This phase is understood as the topological Anderson insulator in non-Hermitian systems. Finally, the disordered phase transition in the cylindrical sample is also investigated. The clean non-Hermitian cylindrical sample has three phases, and such samples show more phase transitions by varying the disorder strength: (1) the normal insulator phase to the gapless phase, (2) the normal insulator phase to the topological Anderson insulator phase, and (3) the gapless phase to the topological Anderson insulator phase.

GENERAL

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Ergodicity recovery of random walk in heterogeneous disordered media Liang Luo(罗亮), Ming Yi(易鸣) Chin. Phys. B, 2020, 29 (5):  050503.  DOI: 10.1088/1674-1056/ab8212 Abstract ( 773 )   HTML   PDF (2541KB) ( 139 )   Significant and persistent trajectory-to-trajectory variance are commonly observed in particle tracking experiments, which have become a major challenge for the experimental data analysis. In this theoretical paper we investigate the ergodicity recovery behavior, which helps clarify the origin and the convergence of trajectory-to-trajectory fluctuation in various heterogeneous disordered media. The concepts of self-averaging and ergodicity are revisited in the context of trajectory analysis. The slow ergodicity recovery and the non-Gaussian diffusion in the annealed disordered media are shown as the consequences of the central limit theorem in different situations. The strange ergodicity recovery behavior is reported in the quenched disordered case, which arises from a localization mechanism. The first-passage approach is introduced to the ergodicity analysis for this case, of which the central limit theorem can be employed and the ergodicity is recovered in the length scale of diffusivity correlation.

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Hidden attractors in a new fractional-order discrete system: Chaos, complexity, entropy, and control Adel Ouannas, Amina Aicha Khennaoui, Shaher Momani, Viet-Thanh Pham, Reyad El-Khazali Chin. Phys. B, 2020, 29 (5):  050504.  DOI: 10.1088/1674-1056/ab820d Abstract ( 784 )   HTML   PDF (11047KB) ( 286 )   This paper studies the dynamics of a new fractional-order discrete system based on the Caputo-like difference operator. This is the first study to explore a three-dimensional fractional-order discrete chaotic system without equilibrium. Through phase portrait, bifurcation diagrams, and largest Lyapunov exponents, it is shown that the proposed fractional-order discrete system exhibits a range of different dynamical behaviors. Also, different tests are used to confirm the existence of chaos, such as 0-1 test and C0 complexity. In addition, the quantification of the level of chaos in the new fractional-order discrete system is measured by the approximate entropy technique. Furthermore, based on the fractional linearization method, a one-dimensional controller to stabilize the new system is proposed. Numerical results are presented to validate the findings of the paper.

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Existence of spontaneous symmetry breaking in two-lane totally asymmetric simple exclusion processes with an intersection Bo Tian(田波), Ping Xia(夏萍), Li Liu(刘莉), Meng-Ran Wu(吴蒙然), Shu-Yong Guo(郭树勇) Chin. Phys. B, 2020, 29 (5):  050505.  DOI: 10.1088/1674-1056/ab820e Abstract ( 634 )   HTML   PDF (555KB) ( 83 )   We study two-lane totally asymmetric simple exclusion processes (TASEPs) with an intersection. Monte Carlo simulations show that only symmetric phases exist in the system. To verify the existence of asymmetric phases, we carry out a cluster mean-field analysis. Analytical results show that the densities of the two upstream segments of the intersection site are always equal, which indicates that the system is not in asymmetric phases. It demonstrates that the spontaneous symmetry breaking does not exist in the system. The density profiles and the boundaries of the symmetric phases are also investigated. We find that the cluster mean-field analysis shows better agreement with simulations than the simple mean-field analysis where the correlation of sites is ignored.

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Analysis of iris-loaded resonance cavity in miniaturized maser Zu-Gen Guo(郭祖根), Yong Zhang(张勇), Tao Tang(唐涛), Zhan-Liang Wang(王战亮), Yu-Bin Gong(宫玉彬), Fei Xiao(肖飞), Hua-Rong Gong(巩华荣) Chin. Phys. B, 2020, 29 (5):  050601.  DOI: 10.1088/1674-1056/ab7d98 Abstract ( 697 )   HTML   PDF (1732KB) ( 105 )   The size reduction of atomic clocks is a long-standing research issue. Many atomic clocks such as passive hydrogen masers (PHMs) and compact rubidium masers (CRMs) use iris-loaded resonance cavities (IRCs) as their microwave cavities because they can dramatically reduce the radical sizes of the atomic clocks. In this paper, the electromagnetic characteristic of the IRC is investigated by a theoretical model based on electromagnetic field theory. The formulas to calculate the resonance frequency, quality factor, and magnetic energy filling factor are presented. The relationship between the IRC structure and its electromagnetic characteristic is clarified. The theoretical calculation results accord well with the electromagnetic software simulations and experimental results. The results in this paper should be helpful in understanding the physical mechanism of the IRC and designing the atomic clocks.

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Hunting problems of multi-quadrotor systems via bearing-based hybrid protocols with hierarchical network Zhen Xu(徐振), Xin-Zhi Liu(刘新芝), Qing-Wei Chen(陈庆伟), Zi-Xing Wu(吴梓杏) Chin. Phys. B, 2020, 29 (5):  050701.  DOI: 10.1088/1674-1056/ab7da2 Abstract ( 755 )   HTML   PDF (2010KB) ( 145 )   Bearing-based hunting protocols commonly adopt a leaderless consensus method, which requests an entire state of the target for each agent and ignores the necessity of collision avoidance. We investigate a hunting problem of multi-quadrotor systems with hybrid bearing protocols, where the quadrotor systems are divided into master and slave groups for reducing the onboard loads and collision avoidance. The masters obtain the entire state of the target, whose hybrid protocols are based on the displacement and bearing constraints to maintain formation and to avoid the collision in the hunting process. However, the slaves' protocols merely depend on the part state of the masters to reduce loads of data transmission. We also investigate the feasibility of receiving the bearing state from machine vision. The simulation results are given to illustrate the effectiveness of the proposed hybrid bearing protocols.

ATOMIC AND MOLECULAR PHYSICS

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Finite-field calculation of electric quadrupole moments of 2P3/2, 2D3/2,5/2, and 2F5/2,7/2 states for Yb+ ion Xi-Tong Guo(郭希同), Yan-Mei Yu(于艳梅), Yong Liu(刘永), Bing-Bing Suo(索兵兵) Chin. Phys. B, 2020, 29 (5):  053101.  DOI: 10.1088/1674-1056/ab821c Abstract ( 650 )   HTML   PDF (546KB) ( 120 )   Electric quadrupole moments of low-lying excited states of Yb+ are calculated by relativistic coupled-cluster theory with perturbations from external fields. The field-dependent energy differentiation provides accurate values of the electric quadrupole moments of 2P3/2, 2D3/2, 5/2, and 2F5/2,7/2 states which agree well with experimental values. The important role of the electronic correlation to the electric quadrupole moments is investigated. Our calculations indicate the early dispute of the electric quadrupole moment of the Yb+(2F7/2) state for which the measured and theoretical values have a large discrepancy. These electric quadrupole moment values can help us to determine the electric quadrupole shifts in start-of-the-art experiments of the Yb+ ion.

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Exploration and elaboration of photo-induced proton transfer dynamical mechanism for novel 2-[1,3]dithian-2-yl-6-(7aH-indol-2-yl)-phenol sensor Lei Xu(许磊), Tian-Jie Zhang(张天杰), Qiao-Li Zhang(张巧丽), Da-Peng Yang(杨大鹏) Chin. Phys. B, 2020, 29 (5):  053102.  DOI: 10.1088/1674-1056/ab8208 Abstract ( 554 )   HTML   PDF (1351KB) ( 109 )   In this work, we theoretically probe into the photo-induced hydrogen bonding effects between S0 state and S1 state as well as the excited state intramolecular proton transfer (ESIPT) behavior for a novel 2-[1,3]dithian-2-yl-6-(7 aH-indol-2-yl)-phenol (DIP) probe system. We first study the ground-state hydrogen bonding O-H…N behavior for DIP. Then we analyze the primary geometrical parameters (i.e., bond length, bond angle, and infrared (IR) stretching vibrational mode) involved in hydrogen bond, and confirm that the O-H…N of DIP should be strengthened in the first excited state. It is the significant prerequisite for ESIPT reaction. Combining the frontier molecular orbitals (MOs) with vertical excitation analyses, the intramolecular charge transfer (ICT) phenomenon can be found for the DIP system, which reveals that the charge redistribution facilitates ESIPT behavior. By constructing potential energy curves for DIP along the ESIPT reactional orientation, we obtain quite a small energy barrier (3.33 kcal/mol) and affirmed that the DIP molecule undergoes ultrafast ESIPT process once it is excited to the S1 state and quickly transfers its proton, forming DIP-keto tautomer. That is why no fluorescence of DIP can be observed in experiment, which further reveals the ultrafast ESIPT mechanism proposed in this work.

SPECIAL TOPIC—Active matters physics

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Phase separation and super diffusion of binary mixtures ofactive and passive particles Yan Wang(王艳), Zhuanglin Shen(谌庄琳), Yiqi Xia(夏益祺), Guoqiang Feng(冯国强), Wende Tian(田文得) Chin. Phys. B, 2020, 29 (5):  053103.  DOI: 10.1088/1674-1056/ab81f4 Abstract ( 816 )   HTML   PDF (1895KB) ( 246 )   Computer simulations were performed to study the dense mixtures of passive particles and active particles in two dimensions. Two systems with different kinds of passive particles (e.g., spherical particles and rod-like particles) were considered. At small active forces, the high-density and low-density regions emerge in both systems, indicating a phase separation. At higher active forces, the systems return to a homogeneous state with large fluctuation of particle area in contrast with the thermo-equilibrium state. Structurally, the rod-like particles accumulate loosely due to the shape anisotropy compared with the spherical particles at the high-density region. Moreover, there exists a positive correlation between Voronoi area and velocity of the particles. Additionally, a small number of active particles capably give rise to super-diffusion of passive particles in both systems when the self-propelled force is turned on.

ATOMIC AND MOLECULAR PHYSICS

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Ab initio studies on ammonium iodine under high pressure Mengya Lu(鲁梦雅), Yanping Huang(黄艳萍), Fubo Tian(田夫波), Da Li(李达), Defang Duan(段德芳), Qiang Zhou(周强), Tian Cui(崔田) Chin. Phys. B, 2020, 29 (5):  053104.  DOI: 10.1088/1674-1056/ab8205 Abstract ( 654 )   HTML   PDF (698KB) ( 140 )   Ammonium iodine (NH4I) as an important member of hydrogen-rich compounds has attracted a great deal of attention owing to its interesting structural changes triggered by the relative orientations of adjacent ammonium ions. Previous studies of ammonium iodide have remained in the low pressure range experimentally, which we first extended to so high pressure (250 GPa). We have investigated the structures of ammonium iodine under high pressure through ab initio evolutionary algorithm and total energy calculations based on density functional theory. The static enthalpy calculations show that phase V is stable until 85 GPa where a new phase Ibam is identified. Calculations of phonon spectra show that the Ibam phase is stable between 85 GPa and 101 GPa and the Cm phase is stable up to 130 GPa. In addition, ammonium iodine dissociates into NH3, H2, and I2 at 74 GPa. Subsequently, we analyzed phonon spectra and electronic band structures, finding that phonon softening is not the reason of dissociation and NH4I is always a semiconductor within the pressure range.

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Semi-integer harmonic generation from an argon atom by bichromatic counter-rotating circularly polarized laser field Tong Qi(齐桐), Xiao-Xin Huo(霍晓鑫), Jun Zhang(张军), Xue-Shen Liu(刘学深) Chin. Phys. B, 2020, 29 (5):  053201.  DOI: 10.1088/1674-1056/ab821b Abstract ( 727 )   HTML   PDF (2404KB) ( 174 )   We theoretically investigated the properties of the high-order harmonic generation from an argon atom by bichromatic counter-rotating circularly polarized (BCCP) laser field. The harmonic emission processes have been illustrated by numerically solving the two-dimensional time-dependent Schrödinger equation of an atom in intense laser fields. It is found that with the decrease of the right-circularly polarized laser wavelength, the harmonic spectra are gradually splitting and the harmonic orders move towards the higher frequency. Meanwhile, the integer and semi-integer harmonic emission will be generated when the frequency ratios of right- and left-circularly polarized lasers are semi-integer. The emission mechanism of the semi-integer-order harmonics has been investigated by using the rules of photon absorption and emission.

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

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Single-order soft x-ray spectra with spectroscopic photon sieve Yu-Lin Gao(高宇林), Lai Wei(魏来), Qiang-Qiang Zhang(张强强), Zu-Zua Yang(杨祖华), Wei-Min Zhou(周维民), Lei-Feng Cao(曹磊峰) Chin. Phys. B, 2020, 29 (5):  054101.  DOI: 10.1088/1674-1056/ab81f0 Abstract ( 710 )   HTML   PDF (2084KB) ( 136 )   A single-order diffraction transmission grating named spectroscopic photon sieve (SPS) for soft x-ray region is proposed and demonstrated in this paper. The SPS consists of many circular pinholes located randomly, and can realize both free-standing diffractions and the suppression of higher-order differations. In this paper, the basic concept, numerical simulations, and calibration results of a 1000-lines/mm SPS for soft x-ray synchrotron radiation are presented. As predicted by theoretical calculations, the calibration results of a 1000-lines/mm SPS verify that the higher-order diffractions can be significantly suppressed along the symmetry axis. With the current nanofabrication technique, the SPS can potentially have a higher line density, and can be widely used in synchrotron radiation, laser-induced plasma diagnostics, and astrophysics.

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Trajectory engineering via a space-fractional Schrödinger equation with dynamic linear index potential Yunji Meng(孟云吉), Youwen Liu(刘友文), Haijiang Lv(吕海江) Chin. Phys. B, 2020, 29 (5):  054201.  DOI: 10.1088/1674-1056/ab7b4c Abstract ( 578 )   HTML   PDF (2995KB) ( 153 )   We theoretically and numerically study the propagation dynamics of a Gaussian beam modeled by the fractional Schrödinger equation with different dynamic linear potentials. For the limited case α=1 (α is the Lévy index) in the momentum space, the beam suffers a frequency shift which depends on the applied longitudinal modulation and the involved chirp. While in the real space, by precisely controlling the linear chirp, the beam will exhibit two different evolution characteristics: one is the zigzag trajectory propagation induced by multi-reflection occurring at the zeros of spatial spectrum, the other is diffraction-free propagation. Numerical simulations are in full accordance with the theoretical results. Increase of the Lévy index not only results in the drift of those turning points along the transverse direction, but also leads to the delocalization of the Gaussian beam.

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Pulse shaping of bright-dark vector soliton pair Yan Zhou(周延), Yuefeng Li(李月锋), Xia Li(李夏), Meisong Liao(廖梅松), Jingshan Hou(侯京山), Yongzheng Fang(房永征) Chin. Phys. B, 2020, 29 (5):  054202.  DOI: 10.1088/1674-1056/ab7b56 Abstract ( 603 )   HTML   PDF (636KB) ( 144 )   We simulate pulse shaping of bright-dark vector soliton pair in an optical fiber system. Through changing input pulse parameters (amplitude ratio, projection angle, time delay, and phase difference), different kinds of pulse shapes and spectra can be generated. For input bright-dark vector soliton pair with the same central wavelength, "2+1"- and "2+2"-type pseudo-high-order bright-dark vector soliton pairs are achieved. While for the case of different central wavelengths, bright-dark vector soliton pairs with multiple pulse peaks/dips are demonstrated with appropriate pulse parameter setting.

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An image compressed sensing algorithm based on adaptive nonlinear network Yuan Guo(郭媛), Wei Chen(陈炜), Shi-Wei Jing(敬世伟) Chin. Phys. B, 2020, 29 (5):  054203.  DOI: 10.1088/1674-1056/ab7b4e Abstract ( 721 )   HTML   PDF (5061KB) ( 159 )   Traditional compressed sensing algorithm is used to reconstruct images by iteratively optimizing a small number of measured values. The computation is complex and the reconstruction time is long. The deep learning-based compressed sensing algorithm can greatly shorten the reconstruction time, but the algorithm emphasis is placed on reconstructing the network part mostly. The random measurement matrix cannot measure the image features well, which leads the reconstructed image quality to be improved limitedly. Two kinds of networks are proposed for solving this problem. The first one is ReconNet's improved network IReconNet, which replaces the traditional linear random measurement matrix with an adaptive nonlinear measurement network. The reconstruction quality and anti-noise performance are greatly improved. Because the measured values extracted by the measurement network also retain the characteristics of image spatial information, the image is reconstructed by bilinear interpolation algorithm (Bilinear) and dilate convolution. Therefore a second network USDCNN is proposed. On the BSD500 dataset, the sampling rates are 0.25, 0.10, 0.04, and 0.01, the average peak signal-noise ratio (PSNR) of USDCNN is 1.62 dB, 1.31 dB, 1.47 dB, and 1.95 dB higher than that of MSRNet. Experiments show the average reconstruction time of USDCNN is 0.2705 s, 0.3671 s, 0.3602 s, and 0.3929 s faster than that of ReconNet. Moreover, there is also a great advantage in anti-noise performance.

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Light slowing and all-optical time division multiplexing of hybrid four-wave mixing signal in nitrogen-vacancy center Ruimin Wang(王瑞敏), Irfan Ahmed, Faizan Raza, Changbiao Li(李昌彪), Yanpeng Zhang(张彦鹏) Chin. Phys. B, 2020, 29 (5):  054204.  DOI: 10.1088/1674-1056/ab7b50 Abstract ( 753 )   HTML   PDF (659KB) ( 139 )   We report the experimental results of hybrid four-wave mixing and fluorescence signals from nitrogen-vacancy (NV) centers in diamond. The fluorescence signals are slowed owing to dark state. The observed delay time of light slowing due to interconversion between NV- and NV0 is about 6.4 μs. The relative intensities of read-out signals change with the wavelength and power of writing pulse. Based on light slowing, we present the model of all-optical time division multiplexing. The intensity ratio in different demultiplexed channels is modulated by the wavelength and power of control field. It has potential applications in quantum communication and all-optical network.

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Cascaded optical frequency transfer over 500-km fiber link using regenerative amplifier Xue Deng(邓雪), Dong-Dong Jiao(焦东东), Jie Liu(刘杰), Qi Zang(臧琦), Xiang Zhang(张翔), Dan Wang(王丹), Jing Gao(高静), Rui-Fang Dong(董瑞芳), Tao Liu(刘涛), Shou-Gang Zhang(张首刚) Chin. Phys. B, 2020, 29 (5):  054205.  DOI: 10.1088/1674-1056/ab7b4f Abstract ( 759 )   HTML   PDF (884KB) ( 198 )   We demonstrate a 300-km+200-km cascaded coherent phase transfer via fiber link. The transfer is divided into a 300-km span and a 200-km span with independent phase locking loops, aiming to extend the phase control bandwidth of the whole link. The phase noise and transfer instability of the cascaded transmission are investigated and compared with those in the case of a single-span 500-km transfer. We achieve the transfer instabilities of 1.8×10-14 at 1 s, 8.9×10-20 at 104 s for the 300-km +200-km cascaded transmission, and 2.7×10-14 at 1 s for the 500-km single-span transfer.

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High common mode rejection ratio InP 90° optical hybrid in ultra-broadband at 60 nm with deep-rigded waveguide based on ×4 MMI coupler Zi-Qing Lu(陆子晴), Qin Han(韩勤), Han Ye(叶焓), Shuai Wang(王帅), Feng Xiao(肖峰), Fan Xiao(肖帆) Chin. Phys. B, 2020, 29 (5):  054206.  DOI: 10.1088/1674-1056/ab7b52 Abstract ( 650 )   HTML   PDF (1002KB) ( 237 )   An InP optical 90° hybrid based on a×4 MMI coupler with a deep ridged waveguide is designed and fabricated. The working principle of the 90° hybrid is systematically introduced. Three-dimensional beam ropagation method (3D BPM) is used to optimize the structure parameters of the 90° hybrid. The designed compact structure is demonatrated to have a low excess loss less than -0.15 dB, a high common mode rejection ratio better than 40 dB, and a low relative phase deviation less than ±2.5°. The designed hybrid is manufactured on a sandwitched structure deposited on an InP substrate. The measured results show that the common mode rejection ratios are larger than 20 dB in a range from 1520 nm to 1580 nm. The phase deviations are less than ±5° in a range from 1545 nm to 1560 nm and less than ±7° across the C band. The designed 90° optical hybrid is suitable well for realizing miniaturization, high-properties, and high bandwidth of coherent receiver.

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High gain fiber-solid hybrid double-passing end-pumped Nd: YVO4 picosecond amplifier with high beam quality Xueyan Dong(董雪岩), Pingxue Li(李平雪), Shun Li(李舜), Dongsheng Wang(王东生) Chin. Phys. B, 2020, 29 (5):  054207.  DOI: 10.1088/1674-1056/ab8218 Abstract ( 702 )   HTML   PDF (1582KB) ( 442 )   We propose a fiber-solid hybrid system which consists of a semiconductor saturable absorber mirror (SESAM) mode-locked fiber seed with a pulse width of 10.2 ps and a repetition rate of 18.9 MHz, a two-level fiber pre-amplifier and a double-passing end-pumped Nd:YVO4 amplifier. In the solid-state amplifier, to enhance the gain and the extraction efficiency, a specially designed structure in which the seed light passes through the gain medium four times and makes full use of population inversion is used as the double-passing amplifier. Besides, the beam filling factor (the ratio of the seed light diameter to the pump light diameter) and the thermal lens effect of the double-passing amplifier are considered and its optical-to-optical conversion efficiency is further improved. To preserve the beam quality of the double-passing amplifier, a new method of spherical-aberration self-compensation based on the principles of geometrical optics is used and discussed. Our system achieves a maximum average power of 9.5 W at the pump power of 28 W, corresponding to an optical-to-optical efficiency of 27%. And the beam quality factor M2 reaches 1.3 at the maximum output power.

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Influences of annealing temperature on properties of Fe2+: ZnSe thin films deposited by electron beam evaporation and their applications to Q-switched fiber laser Du-Xin Qing(卿杜鑫), Shu-Tong Wang(王树同), Shou-Gui Ning(宁守贵), Wei Zhang(张伟), Xiao-Xu Chen(陈晓旭), Hong Zhang(张弘), Guo-Ying Feng(冯国英), Shou-Huan Zhou(周寿桓) Chin. Phys. B, 2020, 29 (5):  054208.  DOI: 10.1088/1674-1056/ab81f2 Abstract ( 617 )   HTML   PDF (1330KB) ( 127 )   Fe2+:ZnSe thin films are prepared on sapphire substrate at room temperature by electron beam evaporation and then annealed in vacuum (about 1×10-4 Pa) at different temperatures. The influences of thermal annealing on the structural and optical properties of these films such as grain size and optical transmittance are investigated. The x-ray diffraction patterns show that the Fe2+:ZnSe thin film is preferred to be oriented along the (111) plane at different annealing temperatures. After the film is annealed, the full-width-at-half-maximum (FWHM ) of the x-ray diffraction peak profile (111) of the film decreases and its crystal quality is improved. Scanning electron microscope images show that the films are more dense after being annealed. Finally, the sample is used as a saturable absorber in ZBLAN fiber laser. The annealed Fe2+:ZnSe thin films can be used to realize stable Q-switching modulation on ZBLAN fiber laser. The results demonstrate that the Fe2+:ZnSe thin film is a promising material for generating the high-power pulses of mid-infrared Q-switched fiber lasers.

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Optical modulation of repaired damage site on fused silica produced by CO2 laser rapid ablation mitigation Chao Tan(谭超), Lin-Jie Zhao(赵林杰), Ming-Jun Chen(陈明君), Jian Cheng(程健), Zhao-Yang Yin(尹朝阳), Qi Liu(刘启), Hao Yang(杨浩), Wei Liao(廖威) Chin. Phys. B, 2020, 29 (5):  054209.  DOI: 10.1088/1674-1056/ab8206 Abstract ( 772 )   HTML   PDF (4312KB) ( 173 )   CO2 laser rapid ablation mitigation (RAM) of fused silica has been used in high-power laser systems owing to its advantages of high efficiency, and ease of implementing batch and automated repairing. In order to study the effect of repaired morphology of RAM on laser modulation and to improve laser damage threshold of optics, an finite element method (FEM) mathematical model of 351 nm laser irradiating fused silica optics is developed based on Maxwell electromagnetic field equations, to explore the 3D near-field light intensity distribution inside optics with repaired site on its surface. The influences of the cone angle and the size of the repaired site on incident laser modulation are studied as well. The results have shown that for the repaired site with a cone angle of 73.3°, the light intensity distribution has obvious three-dimensional characteristics. The relative light intensity on z-section has a circularly distribution, and the radius of the annular intensification zone increases with the decrease of z. While the distribution of maximum relative light intensity on y-section is parabolical with the increase of y. As the cone angle of the repaired site decreases, the effect of the repaired surface on light modulation becomes stronger, leading to a weak resistance to laser damage. Moreover, the large size repaired site would also reduce the laser damage threshold. Therefore, a repaired site with a larger cone angle and smaller size is preferred in practical CO2 laser repairing of surface damage. This work will provide theoretical guidance for the design of repaired surface topography, as well as the improvement of RAM process.

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Narrowband perfect terahertz absorber based on polar-dielectrics metasurface Meng-Meng Zhao(赵萌萌), Shu-Fang Fu(付淑芳), Sheng Zhou(周胜), Yu-Ling Song(宋玉玲), Qiang Zhang(张强), Yong-Qi Yin(尹永琦), Yu-Tian Zhao(赵玉田), Hong Liang(梁红), Xuan-Zhang Wang(王选章) Chin. Phys. B, 2020, 29 (5):  054210.  DOI: 10.1088/1674-1056/ab81fa Abstract ( 638 )   HTML   PDF (1784KB) ( 215 )   We theoretically propose a narrowband perfect absorber metasurface (PAMS) based on surface phonon polaritons in the terahertz range. The PAMS has unit cell consisting of a silver biarc on the top, a thin polar-dielectric in the middle and a silver layer at the bottom. The phonon polaritons are excited at the interface between the silver biarc and the polar dielectric, and enhance the absorption of the PAMS. The absorption peak is at 36.813 μm and the full width half maximum (FWHM) is nearly 36 nm, independent of the polarization and incidence angle. The electric fields are located at the split of the biarc silver layer and the quality factor Q is 1150. The FWHM decreases with the decreasing split width. When the thickness of the bottom layer is larger than 50 nm, the narrow band and high absorption are insensitive to the thickness of those layers. The designed absorber may have useful applications in terahertz spectra such as energy harvesting, thermal emitter, and sensing.

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Electromagnetically induced transparency and electromagnetically induced absorption in Y-type system Kalan Mal, Khairul Islam, Suman Mondal, Dipankar Bhattacharyya, Amitava Bandyopadhyay Chin. Phys. B, 2020, 29 (5):  054211.  DOI: 10.1088/1674-1056/ab7ea0 Abstract ( 842 )   HTML   PDF (537KB) ( 233 )   The propagation of a probe field through a four-level Y-type atomic system is described in the presence of two additional coherent radiation fields, namely, the control field and the coupling field. An expression for the probe response is derived analytically from the optical Bloch equations under steady state condition to study the absorptive properties of the system under probe field propagation through an ensemble of stationary atoms as well as in a Doppler broadened atomic vapor medium. The most striking result is the conversion of electromagnetically induced transparency (EIT) into electromagnetically induced absorption (EIA) as we start switching from weak probe regime to strong probe regime. The dependence of this conversion on residual Doppler averaging due to wavelength mismatch is also shown by choosing the coupling transition as a Rydberg transition.

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Location of micro-cracks in plates using time reversed nonlinear Lamb waves Yaoxin Liu(刘尧鑫), Aijun He(何爱军), Jiehui Liu(刘杰惠), Yiwei Mao(毛一葳), Xiaozhou Liu(刘晓宙) Chin. Phys. B, 2020, 29 (5):  054301.  DOI: 10.1088/1674-1056/ab81f7 Abstract ( 706 )   HTML   PDF (790KB) ( 156 )   A promising tool to detect micro-cracks in plate-like structures is used for generating higher harmonic Lamb waves. In this paper, a method combining nonlinear S0 mode Lamb waves with time reversal to locate micro-cracks is presented and verified by numerical simulations. Two different models, the contact acoustic nonlinearity (CAN) model and the Preisach-Mayergoyz (PM) model, are used to simulate a localized damage in a thin plate. Pulse inversion method is employed to extract the second and fourth harmonics from the received signal. Time reversal is performed to compensate the dispersion of S0 mode Lamb waves. Consequently, the higher harmonics generated from the damaged area can be refocused on their source. By investigating the spatial distribution of harmonic wave packets, the location of micro-cracks will be revealed. The numerical simulations indicate that this method gives accurate locations of the damaged area in a plate. Furthermore, the PM model is proved to be a suitable model to simulate the micro-cracks in plates for generation of higher harmonics.

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Pulling force of acoustic-vortex beams on centered elastic spheres based on the annular transducer model Yuzhi Li(李禹志), Qingdong Wang(王青东), Gepu Guo(郭各朴), Hongyan Chu(褚红燕), Qingyu Ma(马青玉), Juan Tu(屠娟), Dong Zhang(章东) Chin. Phys. B, 2020, 29 (5):  054302.  DOI: 10.1088/1674-1056/ab8210 Abstract ( 816 )   HTML   PDF (1454KB) ( 165 )   To solve the difficulty of generating an ideal Bessel beam, an simplified annular transducer model is proposed to study the axial acoustic radiation force (ARF) and the corresponding negative ARF (pulling force) exerted on centered elastic spheres for acoustic-vortex (AV) beams of arbitrary orders. Based on the theory of acoustic scattering, the axial distributions of the velocity potential and the ARF for AV beams of different orders generated by the annular transducers with different physical sizes are simulated. It is proved that the pulling force can be generated by AV beams of arbitrary orders with multiple axial regions. The pulling force is more likely to exert on the sphere with a smaller k0a (product of the wave number and the radius) for the AV beam with a bigger topological charge due to the strengthened off-axis acoustic scattering. The pulling force decreases with the increase of the axial distance for the sphere with a bigger k0a. More pulling force areas with wider axial regions can be formed by AV beams using a bigger-sized annular transducer. The theoretical results demonstrate the feasibility of generating the pulling force along the axes of AV beams using the experimentally applicable circular array of planar transducers, and suggest application potentials for multi-position stable object manipulations in biomedical engineering.

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Single SH guided wave mode generation method for PPM EMATs Guo-Fu Zhai(翟国富), Yong-Qian Li(李永虔) Chin. Phys. B, 2020, 29 (5):  054303.  DOI: 10.1088/1674-1056/ab81f8 Abstract ( 658 )   HTML   PDF (1335KB) ( 145 )   Using periodic permanent magnet (PPM) electromagnetic acoustic transducers (EMATs), different shear horizontal (SH) guided wave modes can form simultaneously in some situations, which can interfere with the inspection. The main cause of this phenomenon (typically named multiple modes) is related to the frequency bandwidth of excitation signals and the transducer spatial bandwidth. Simply narrowing the frequency bandwidth cannot effectively limit the number of different SH modes. Previous researches showed that unnecessary SH wave modes can be eliminated by using dual EMATs. However, in practical applications, it is more convenient to change the excitation frequency than to use dual EMATs. In this paper, the stress boundary conditions of the PPM-EMAT are analyzed, the analytical expression of SH guided wave is established, and the magnitude of SH guided wave mode under continuous tone and tone-burst input is obtained. A method to generate a single SH mode by re-selecting an operating point is proposed. Furthermore, the influence of the frequency bandwidth of the tone-burst signal is analyzed. Finally, a single SH mode excitation is achieved with tone-burst input.

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Efficient tensor decomposition method for noncircular source in colocated coprime MIMO radar Qian-Peng Xie(谢前朋), Xiao-Yi Pan(潘小义), Shun-Ping Xiao(肖顺平) Chin. Phys. B, 2020, 29 (5):  054304.  DOI: 10.1088/1674-1056/ab81f6 Abstract ( 637 )   HTML   PDF (859KB) ( 115 )   An effective method via tensor decomposition is proposed to deal with the joint direction-of-departure (DOD) and direction-of-arrival (DOA) estimation of noncircular sources in colocated coprime MIMO radar. By decomposing the transmitter and receiver into two sparse subarrays, noncircular property of source can be used to construct new extended received signal model for two sparse subarrays. The new received model can double the virtual array aperture due to the elliptic covariance of imping sources is nonzero. To further exploit the multidimensional structure of the noncircular received model, we stack the subarray output and its conjugation according to mode-1 unfolding and mode-2 unfolding of a third-order tensor, respectively. Thus, the corresponding extended tensor model consisted of noncircular information for DOA and DOD can be obtained. Then, the higher-order singular value decomposition technique is utilized to estimate the accurate signal subspace and angular parameter can be automatically paired via the rotational invariance relationship. Specifically, the ambiguous angle can be eliminated and the true targets can be achieved with the aid of the coprime property. Furthermore, a closed-form expression for the deterministic CRB under the NC sources scenario is also derived. Simulation results verify the superiority of the proposed estimator.

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Magnetoacoustic position imaging for liquid metal in animal interstitial structure Xiao-He Zhao(赵筱赫), Guo-Qiang Liu(刘国强), Hui Xia(夏慧), Yan-Hong Li(李艳红) Chin. Phys. B, 2020, 29 (5):  054305.  DOI: 10.1088/1674-1056/ab8207 Abstract ( 661 )   HTML   PDF (1411KB) ( 136 )   Magnetoacoustic tomography with magnetic induction (MAT-MI), as a new kind of in-vivo imaging method, has potential application value in interstitial fluid research. In this paper, we propose the application of MAT-MI with liquid metal serving as a tracer of the interstitial structure to study its fluid behavior, and use it to implement the positional imaging of the spatial distribution of liquid metal. Owing to the particularity of liquid metal magnetoacoustic pressure (MAP) signals, we propose an envelope analysis method to extract the rising edge of the amplitude envelope of the detected waveform as effective position data. And for the first time, we propose the method of superpositing pixel matrix to achieve the position imaging of liquid metal. Finally, the positional imaging of the liquid metal sample embedded in the gel is achieved to have relatively accurate results. This study provides a method of effectively extracting data and implementing the position imaging for liquid metal in the interstitial structure in the frame of MAT-MI.

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Growth induced buckling of morphoelastic rod in viscous medium Yitong Zhang(张一桐), Shuai Zhang(张帅), Peng Wang(王鹏) Chin. Phys. B, 2020, 29 (5):  054501.  DOI: 10.1088/1674-1056/ab7b4d Abstract ( 643 )   HTML   PDF (316KB) ( 108 )   Biological growth is a common phenomenon in nature, and some organisms such as DNA molecules and bacterial filaments grow in viscous media. The growth induced instability of morphoelastic rod in a viscous medium is studied in this paper. Based on the Kirchhoff kinetic analogy method, the mechanical model for growing elastic thin rod in the viscous medium is established. A perturbation analysis is used to analyze the stability of the growing elastic rod in the viscous medium. We apply the results into planar growing ring and get its criterion of instability. Take the criterion into DNA ring to discuss the influence of viscous resistance on its instability.

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Parametric study of the clustering transition in vibration driven granular gas system Qi-Lin Wu(吴麒麟), Mei-Ying Hou(厚美瑛), Lei Yang(杨磊), Wei Wang(王伟), Guang-Hui Yang(杨光辉), Ke-Wei Tao(陶科伟), Liang-Wen Chen(陈良文), Sheng Zhang(张晟) Chin. Phys. B, 2020, 29 (5):  054502.  DOI: 10.1088/1674-1056/ab8217 Abstract ( 701 )   HTML   PDF (2043KB) ( 153 )   A parametric study of the clustering transition of a vibration-driven granular gas system is performed by simulation. The parameters studied include the global volume fraction of the system, the size of the system, the friction coefficient, and the restitution coefficient among particles and among particle-walls. The periodic boundary and fixed boundary of sidewalls are also checked in the simulation. The simulation results provide us the necessary "heating" time for the system to reach steady state, and the friction term needed to be included in the "cooling" time. A gas-cluster phase diagram obtained through Kolmogorov-Smirnov (K-S) test analysis using similar experimental parameters is given. The influence of the parameters to the transition is then investigated in simulations. This simulation investigation helps us gain understanding which otherwise cannot be obtained by experiment alone, and makes suggestions on the determination of parameters to be chosen in experiments.

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Numerical study on permeability characteristics of fractal porous media Yongping Huang(黄永平), Feng Yao(姚峰), Bo Zhou(周博), Chengbin Zhang(张程宾) Chin. Phys. B, 2020, 29 (5):  054701.  DOI: 10.1088/1674-1056/ab7b53 Abstract ( 831 )   HTML   PDF (2660KB) ( 148 )   The fractal Brownian motion is utilized to describe pore structures in porous media. A numerical model of laminar flow in porous media is developed, and the flow characteristics are comprehensively analyzed and compared with those of homogeneous porous media. Moreover, the roles of the fractal dimension and porosity in permeability are quantitatively described. The results indicate that the pore structures of porous media significantly affect their seepage behaviors. The distributions of pressure and velocity in fractal porous media are both non-uniform; the streamline is no longer straight but tortuous. When Reynolds number Re < 1, the dimensionless permeability is independent of Reynolds number, but its further increase will lead to a smaller permeability. Moreover, due to the higher connectivity and enlarged equivalent aperture of internal channel network, the augment in porosity leads to the permeability enhancement, while it is small and insensitive to porosity variation when ε < 0.6. Fractal dimension also plays a significant role in the permeability of porous media. The increase in fractal dimension leads to the enhancement in pore connectivity and a decrease in channel tortuosity, which reduces the flow resistance and improves the transport capacity of porous media.

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Droplets breakup via a splitting microchannel Wei Gao(高崴), Cheng Yu(于程), Feng Yao(姚峰) Chin. Phys. B, 2020, 29 (5):  054702.  DOI: 10.1088/1674-1056/ab7b4b Abstract ( 533 )   HTML   PDF (3148KB) ( 194 )   On the basis of a volume of fluid (VOF) liquid/liquid interface tracking method, we apply a two-dimensional model to investigate the dynamic behaviors of droplet breakup through a splitting microchannel. The feasibility and applicability of the theoretical model are experimentally validated. Four flow regimes are observed in the splitting microchannel, that is, breakup with permanent obstruction, breakup with temporary obstruction, breakup with tunnels, and non-breakup. The results indicate that the increase of the capillary number Ca provides considerable upstream pressure to accelerate the droplet deformation, which is favorable for the droplet breakup. The decrease of the droplet size contributes to its shape changing from the plug to the sphere, which results in weakening droplet deformation ability and generating the non-breakup flow regime.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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Magnetic properties of La2CuMnO6 double perovskite ceramic investigated by Monte Carlo simulations S Mtougui, I EL Housni, N EL Mekkaoui, S Ziti, S Idrissi, H Labrim, R Khalladi, L Bahmad Chin. Phys. B, 2020, 29 (5):  056101.  DOI: 10.1088/1674-1056/ab7d95 Abstract ( 592 )   HTML   PDF (515KB) ( 291 )   We present a theoretical study of the magnetic properties of the lanthanum copper manganate double perovskite La2CuMnO6 ceramic, using Monte Carlo simulations. We analyze and discuss the ground state phase diagrams in different planes to show the effect of every physical parameter. Based on the Monte Carlo simulations, which combine Metropolis algorithm and Ising model, we explore the thermal behavior of the total magnetization and susceptibility. We also present and discuss the influence of physical parameters such as the external magnetic field, the exchange coupling interactions between magnetic atoms, and the exchange magnetic field on the magnetization of the system. Moreover, the critical temperature of the system is about Tc=70 K, in agreement with the experimental value. Finally, the hysteresis loops of La2CuMnO6 are discussed.

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Modification of the Peierls-Nabarro model for misfit dislocation Shujun Zhang(张淑君), Shaofeng Wang(王少峰) Chin. Phys. B, 2020, 29 (5):  056102.  DOI: 10.1088/1674-1056/ab8459 Abstract ( 645 )   HTML   PDF (505KB) ( 113 )   For a misfit dislocation, the balance equations satisfied by the displacement fields are modified, and an extra term proportional to the second-order derivative appears in the resulting misfit equation compared with the equation derived by Yao et al. This second-order derivative describes the lattice discreteness effect that arises from the surface effect. The core structure of a misfit dislocation and the change in interfacial spacing that it induces are investigated theoretically in the framework of an improved Peierls-Nabarro equation in which the effect of discreteness is fully taken into account. As an application, the structure of the misfit dislocation for a honeycomb structure in a two-dimensional heterostructure is presented.

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Bose-Einstein condensates in an eightfold symmetric optical lattice Zhen-Xia Niu(牛真霞), Yong-Hang Tai(邰永航), Jun-Sheng Shi(石俊生), Wei Zhang(张威) Chin. Phys. B, 2020, 29 (5):  056103.  DOI: 10.1088/1674-1056/ab8211 Abstract ( 927 )   HTML   PDF (971KB) ( 141 )   We investigate the properties of Bose-Einstein condensates (BECs) in a two-dimensional quasi-periodic optical lattice (OL) with eightfold rotational symmetry by numerically solving the Gross-Pitaevskii equation. In a stationary external harmonic trapping potential, we first analyze the evolution of matter-wave interference pattern from periodic to quasi-periodic as the OL is changed continuously from four-fold periodic to eight-fold quasi-periodic. We also investigate the transport properties during this evolution for different interatomic interaction and lattice depth, and find that the BEC crosses over from ballistic diffusion to localization. Finally, we focus on the case of eightfold symmetric lattice and consider a global rotation imposed by the external trapping potential. The BEC shows vortex pattern with eightfold symmetry for slow rotation, becomes unstable for intermediate rotation, and exhibits annular solitons with approximate axial symmetry for fast rotation. These results can be readily demonstrated in experiments using the same configuration as in Phys. Rev. Lett. 122 110404 (2019).

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Electronic structure and phase transition engineering in NbS2: Crucial role of van der Waals interactions Wei Wang(王威), Wen Lei(雷文), Xiaojun Zheng(郑晓军), Huan Li(黎欢), Xin Tang(唐鑫), Xing Ming(明星) Chin. Phys. B, 2020, 29 (5):  056201.  DOI: 10.1088/1674-1056/ab8214 Abstract ( 679 )   HTML   PDF (1812KB) ( 270 )   Based on first-principles simulations, we revisit the crystal structures, electronic structures, and structural stability of the layered transition metal dichalcogenides (TMDCs) NbS2, and shed more light on the crucial roles of the van der Waals (vdW) interactions. Theoretically calculated results imply that the vdW corrections are important to reproduce the layered crystal structure, which is significant to correctly describe the electronic structure of NbS2. More interestingly, under hydrostatic pressure or tensile strain in ab plane, an isostructural phase transition from two-dimensional layered structure to three-dimensional bulk in the I4/mmm phase has been uncovered. The abnormal structural transition is closely related to the electronic structure instability and interlayer bonding effects. The interlayer Nb-S distances collapse and the interlayer vdW interactions disappear, concomitant with new covalent bond emerging and increasing coordination number. Present work highlights the significance of the vdW interactions, and provides new insights on the unconventional structural transitions in NbS2, which will attract wide audience working in the hectic field of TMDCs.

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Effect of chemical ordering annealing on superelasticity of Ni-Mn-Ga-Fe ferromagnetic shape memory alloy microwires Yanfen Liu(刘艳芬), Xuexi Zhang(张学习), Hongxian Shen(沈红先), Jianfei Sun(孙剑飞), Qinan Li(李奇楠), Xiaohua Liu(刘晓华), Jianjun Li(李建军), Weidong Cheng(程伟东) Chin. Phys. B, 2020, 29 (5):  056202.  DOI: 10.1088/1674-1056/ab8213 Abstract ( 707 )   HTML   PDF (1973KB) ( 133 )   Ni50Mn25Ga20Fe5 ferromagnetic shape memory alloy microwires with diameters of ～30-50μm and grain sizes of ～2-5μm were prepared by melt-extraction technique. A step-wise chemical ordering annealing was carried out to improve the superelasticity strain and recovery ratio which were hampered by the internal stress, compositional inhomogeneity, and high-density defects in the as-extracted Ni50Mn25Ga20Fe5 microwires. The annealed microwires exhibited enhanced atomic ordering degree, narrow thermal hysteresis, and high saturation magnetization under a low magnetic field. As a result, the annealed microwire showed decreased superelastic critical stress, improved reversibility, and a high superelastic strain (1.9%) with a large recovery ratio (>96%). This kind of filamentous material with superior superelastic effects may be promising materials for minor-devices.

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Raman scattering study of two-dimensional magnetic van der Waals compound VI3 Yi-Meng Wang(王艺朦), Shang-Jie Tian(田尚杰), Cheng-He Li(李承贺), Feng Jin(金峰), Jian-Ting Ji(籍建葶), He-Chang Lei(雷和畅), Qing-Ming Zhang(张清明) Chin. Phys. B, 2020, 29 (5):  056301.  DOI: 10.1088/1674-1056/ab8215 Abstract ( 782 )   HTML   PDF (594KB) ( 365 )   The layered magnetic van der Waals materials have generated tremendous interest due to their potential applications and importance in fundamental research. Previous x-ray diffraction (XRD) studies on the magnetic van der Waals compound VI3, revealed a structural transition above the magnetic transition but output controversial analysis on symmetry. In this paper we carried out polarized Raman scattering measurements on VI3 from 10 K to 300 K, with focus on the two Ag phonon modes at ～ 71.1 cm-1 and 128.4 cm-1. Our careful symmetry analysis based on the angle-dependent spectra demonstrates that the crystal symmetry can be well described by C2h rather than D3d both above and below structural phase transition. We further performed temperature-dependent Raman experiments to study the magnetism in VI3. Fano asymmetry and anomalous linewidth drop of two Ag phonon modes at low temperatures, point to a significant spin-phonon coupling. This is also supported by the softening of 71.1-cm-1 mode above the magnetic transition. The study provides the fundamental information on lattice dynamics and clarifies the symmetry in VI3. And spin-phonon coupling existing in a wide temperature range revealed here may be meaningful in applications.

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Effect of Ni substitution on the formability and magnetic properties of Gd50Co50 amorphous alloy Ben-Zheng Tang(唐本镇), Xiao-Ping Liu(刘晓萍), Dong-Mei Li(李冬梅), Peng Yu(余鹏), Lei Xia(夏雷) Chin. Phys. B, 2020, 29 (5):  056401.  DOI: 10.1088/1674-1056/ab7da8 Abstract ( 699 )   HTML   PDF (563KB) ( 124 )   A small amount of Ni was added into the binary Gd50Co50 amorphous alloy to replace Gd in order to obtain ternary Co50Gd50-xNx (x= 1, 2, and 3) amorphous alloys. Compared to the binary Gd50Co50 amorphous alloy, the Co50Gd50-xNx amorphous alloys show an enhanced Curie temperature (TC) with a weakened formability. The maximum magnetic entropy change (-ΔSmpeak) of the Co50Gd50-xNx amorphous alloys is found to decrease with the increasing TC. The adiabatic temperature rise (ΔTad) of the Co50Gd47Ni3 amorphous alloy is superior to that of the Fe-based metallic glasses at room temperature. The variation of the TC and -ΔSmpeak of the Gd50Co50 amorphous alloy with Ni addition, and the mechanism involved, were discussed.

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Growth and structural characteristics of metastable β-In2Se3 thin films on H-terminated Si(111) substrates by molecular beam epitaxy Yi-Fan Shen(沈逸凡), Xi-Bo Yin(尹锡波), Chao-Fan Xu(徐超凡), Jing He(贺靖), Jun-Ye Li(李俊烨), Han-Dong Li(李含冬), Xiao-Hong Zhu(朱小红), Xiao-Bin Niu(牛晓滨) Chin. Phys. B, 2020, 29 (5):  056402.  DOI: 10.1088/1674-1056/ab820f Abstract ( 702 )   HTML   PDF (1326KB) ( 255 )   Epitaxial growth and structural characteristics of metastable β-In2Se3 thin films on H-terminated Si(111) substrates are studied. The In2Se3 thin films grown below the β-to-α phase transition temperature (453 K) are characterized to be strained β-In2Se3 mixed with significant γ-In2Se3 phases. The pure-phased single-crystalline β-In2Se3 can be reproducibly achieved by in situ annealing the as-deposited poly-crystalline In2Se3 within the phase equilibrium temperature window of β-In2Se3. It is suggeted that the observed γ-to-β phase transition triggered by quite a low annealing temperature should be a rather lowered phase transition barrier of the epitaxy-stabilized In2Se3 thin-film system at a state far from thermodynamic equilibrium.

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STM study of selenium adsorption on Au(111) surface Bin Liu(刘斌), Yuan Zhuang(庄源), Yande Que(阙炎德), Chaoqiang Xu(徐超强), Xudong Xiao(肖旭东) Chin. Phys. B, 2020, 29 (5):  056801.  DOI: 10.1088/1674-1056/ab821d Abstract ( 794 )   HTML   PDF (1329KB) ( 189 )   Adsorption of chalcogen atoms on metal surfaces has attracted increasing interest for both the fundamental research and industrial applications. Here, we report a systematic study of selenium (Se) adsorption on Au(111) at varies substrate temperatures by scanning tunneling microscopy. At room temperature, small Se clusters are randomly dispersed on the surface. Increasing the temperature up to 200℃, a well-ordered lattice of Se molecules consisting of 8 Se atoms in ring-like structure is formed. Further increasing the temperature to 250℃ gives rise to the formation of Se monolayer with Au(111)-√3×√3 lattices superimposed with a quasi-hexagonal lattice. Desorption of Se atoms rather than the reaction between the Se atoms and the Au substrate occurs if further increasing the temperature. The ordered structures of selenium monolayers could serve as templates for self-assemblies and our findings in this work might provide insightful guild for the epitaxial growth of the two-dimensional transition metal dichalcogenides.

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

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Influence of spherical inclusions on effective thermoelectric properties of thermoelectric composite materials Wen-Kai Yan(闫文凯), Ai-Bing Zhang(张爱兵), Li-Jun Yi(易利军), Bao-Lin Wang(王保林), Ji Wang(王骥) Chin. Phys. B, 2020, 29 (5):  057301.  DOI: 10.1088/1674-1056/ab7d96 Abstract ( 698 )   HTML   PDF (688KB) ( 182 )   A homogenization theory is developed to predict the influence of spherical inclusions on the effective thermoelectric properties of thermoelectric composite materials based on the general principles of thermodynamics and Mori-Tanaka method. The closed-form solutions of effective Seebeck coefficient, electric conductivity, heat conductivity, and figure of merit for such thermoelectric materials are obtained by solving the nonlinear coupled transport equations of electricity and heat. It is found that the effective figure of merit of thermoelectric material containing spherical inclusions can be higher than that of each constituent in the absence of size effect and interface effect. Some interesting examples of actual thermoelectric composites with spherical inclusions, such as insulated cavities, inclusions subjected to conductive electric and heat exchange and thermoelectric inclusions, are considered, and the numerical results lead to the conclusion that considerable enhancement of the effective figure of merit is achievable by introducing inclusions. In this paper, we provide a theoretical foundation for analytically and computationally treating the thermoelectric composites with more complicated inclusion structures, and thus pointing out a new route to their design and optimization.

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Selective excitation of multipolar surface plasmon in a graphene-coated dielectric particle by Laguerre Gaussian beam Yang Yang(杨阳), Guanghua Zhang(张光华), Xiaoyu Dai(戴小玉) Chin. Phys. B, 2020, 29 (5):  057302.  DOI: 10.1088/1674-1056/ab7e97 Abstract ( 495 )   HTML   PDF (964KB) ( 117 )   Localized surface plasmonic resonance has attracted extensive attention since it allows for great enhancement of local field intensity on the nanoparticle surface. In this paper, we make a systematic study on the excitation of localized surface plasmons of a graphene coated dielectric particle. Theoretical results show that both the intensity and frequency of the plasmonic resonant peak can be tuned effectively through modifying the graphene layer. Furthermore, high order localized surface plasmons could be excited and tuned selectively by the Laguerre Gaussian beam, which is induced by the optical angular orbital momentum transfer through the mutual interaction between the particle and the helical wavefront. Moreover, the profiles of the multipolar localized surface plasmons are illustrated in detail. The study provides rich potential applications in the plasmonic devices and the wavefront engineering nano-optics.

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Seeing Dirac electrons and heavy fermions in new boron nitride monolayers Yu-Jiao Kang(康玉娇), Yuan-Ping Chen(陈元平), Jia-Ren Yuan(袁加仁), Xiao-Hong Yan(颜晓红), Yue-E Xie(谢月娥) Chin. Phys. B, 2020, 29 (5):  057303.  DOI: 10.1088/1674-1056/ab7e9e Abstract ( 656 )   HTML   PDF (2222KB) ( 327 )   Most three-dimensional (3D) and two-dimensional (2D) boron nitride (BN) structures are wide-band-gap insulators. Here, we propose two BN monolayers having Dirac points and flat bands, respectively. One monolayer is named as 5-7 BN that consists of five- and seven-membered rings. The other is a Kagome BN made of triangular boron rings and nitrogen dimers. The two structures show not only good dynamic and thermodynamic stabilities but also novel electronic properties. The 5-7 BN has Dirac points on the Fermi level, indicating that the structure is a typical Dirac material. The Kagome BN has double flat bands just below the Fermi level, and thus there are heavy fermions in the structure. The flat-band-induced ferromagnetism is also revealed. We analyze the origination of the band structures by partial density of states and projection of orbitals. In addition, a possible route to experimentally grow the two structures on some suitable substrates such as the PbO2 (111) surface and the CdO (111) surface is also discussed, respectively. Our research not only extends understanding on the electronic properties of BN structures, but also may expand the applications of BN materials in 2D electronic devices.

TOPICAL REVIEW—Topological 2D materials

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Topology and ferroelectricity in group-V monolayers Mutee Ur Rehman, Chenqiang Hua(华陈强), Yunhao Lu(陆赟豪) Chin. Phys. B, 2020, 29 (5):  057304.  DOI: 10.1088/1674-1056/ab81ff Abstract ( 866 )   HTML   PDF (5383KB) ( 699 )   The group-V monolayers (MLs) have been studied intensively after the experimental fabrication of two-dimensional (2D) graphene and black phosphorus. The observation of novel quantum phenomena, such as quantum spin Hall effect and ferroelectricity in group-V elemental layers, has attracted tremendous attention because of the novel physics and promising applications for nanoelectronics in the 2D limit. In this review, we comprehensively review recent research progress in engineering of topology and ferroelectricity, and several effective methods to control the quantum phase transition are discussed. We then introduce the coupling between topological orders and ferroelectric orders. The research directions and outlooks are discussed at the end of the perspective. It is expected that the comprehensive overview of topology and ferroelectricity in 2D group-V materials can provide guidelines for researchers in the area and inspire further explorations of interplay between multiple quantum phenomena in low-dimensional systems.

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

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Dynamics of entropic uncertainty for three types of three-level atomic systems under the random telegraph noise Xiong Xu(许雄), Mao-Fa Fang(方卯发) Chin. Phys. B, 2020, 29 (5):  057305.  DOI: 10.1088/1674-1056/a67e9c Abstract ( 695 )   HTML   PDF (1732KB) ( 113 )   We study the dynamics of the entropic uncertainty for three types of three-level atomic systems coupled to an environment modeled by random matrices. The results show that the entropic uncertainty in the Ξ-type atomic system is lower than that in the V-type atomic system which is exactly the same as that in the Λ-type atomic system. In addition, the effect of relative coupling strength on entropic uncertainty is opposite in Markov region and non-Markov region, and the influence of a common environment and independent environments in Markov region and non-Markov region is also opposite. One can reduce the entropic uncertainty by decreasing relative coupling strength or placing the system in two separate environments in the Markov case. In the non-Markov case, the entropic uncertainty can be reduced by increasing the relative coupling strength or by placing the system in a common environment.

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Improvements in reverse breakdown characteristics of THz GaAs Schottky barrier varactor based on metal-brim structure Lu-Wei Qi(祁路伟), Xiao-Yu Liu(刘晓宇), Jin Meng(孟进), De-Hai Zhang(张德海), Jing-Tao Zhou(周静涛) Chin. Phys. B, 2020, 29 (5):  057306.  DOI: 10.1088/1674-1056/ab81fc Abstract ( 676 )   HTML   PDF (874KB) ( 137 )   The excellent reverse breakdown characteristics of Schottky barrier varactor (SBV) are crucially required for the application of high power and high efficiency multipliers. The SBV with a novel Schottky structure named metal-brim is fabricated and systemically evaluated. Compared with normal structure, the reverse breakdown voltage of the new type SBV improves from -7.31 V to -8.75 V. The simulation of the Schottky metal-brim SBV is also proposed. Three factors, namely distribution of leakage current, the electric field, and the area of space charge region are mostly concerned to explain the physical mechanism. Schottky metal-brim structure is a promising approach to improve the reverse breakdown voltage and reduce leakage current by eliminating the accumulation of charge at Schottky electrode edge.

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High performance InAlN/GaN high electron mobility transistors for low voltage applications Minhan Mi(宓珉瀚), Meng Zhang(张濛), Sheng Wu(武盛), Ling Yang(杨凌), Bin Hou(侯斌), Yuwei Zhou(周雨威), Lixin Guo(郭立新), Xiaohua Ma(马晓华), Yue Hao(郝跃) Chin. Phys. B, 2020, 29 (5):  057307.  DOI: 10.1088/1674-1056/ab821e Abstract ( 789 )   HTML   PDF (1214KB) ( 230 )   A high performance InAlN/GaN high electron mobility transistor (HEMT) at low voltage operation (6-10 V drain voltage) has been fabricated. An 8 nm InAlN barrier layer is adopted to generate large 2DEG density thus to reduce sheet resistance. Highly scaled lateral dimension (1.2 μm source-drain spacing) is to reduce access resistance. Both low sheet resistance of the InAlN/GaN structure and scaled lateral dimension contribute to an high extrinsic transconductance of 550 mS/mm and a large drain current of 2.3 A/mm with low on-resistance (Ron) of 0.9 Ω·mm. Small signal measurement shows an fT/fmax of 131 GHz/196 GHz. Large signal measurement shows that the InAlN/GaN HEMT can yield 64.7%-52.7% (Vds=6-10 V) power added efficiency (PAE) associated with 1.6-2.4 W/mm output power density at 8 GHz. These results demonstrate that GaN-based HEMTs not only have advantages in the existing high voltage power and high frequency rf field, but also are attractive for low voltage mobile compatible rf applications.

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Application of graphene vertical field effect to regulation of organic light-emitting transistors Hang Song(宋航), Hao Wu(吴昊), Hai-Yang Lu(陆海阳), Zhi-Hao Yang(杨志浩), Long Ba(巴龙) Chin. Phys. B, 2020, 29 (5):  057401.  DOI: 10.1088/1674-1056/ab81f3 Abstract ( 644 )   HTML   PDF (1772KB) ( 136 )   The luminescence intensity regulation of organic light-emitting transistor (OLED) device can be achieved effectively by the combination of graphene vertical field effect transistor (GVFET) and OLED. In this paper, we fabricate and characterize the graphene vertical field-effect transistor with gate dielectric of ion-gel film, confirming that its current switching ratio reaches up to 102. Because of the property of high light transmittance in ion-gel film, the OLED device prepared with graphene/PEDOT:PSS as composite anode exhibits good optical properties. We also prepare the graphene vertical organic light-emitting field effect transistor (GVOLEFET) by the combination of GVFET and graphene OLED, analyzing its electrical and optical properties, and confirming that the luminescence intensity can be significantly changed by regulating the gate voltage.

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Effect of annealing temperature on coercivity of Nd-Fe-B magnets with TbFeAl doping by process of hot-pressing Ze-Teng Shu(舒泽腾), Bo Zheng(郑波), Guang-Fei Ding(丁广飞), Shi-Cong Liao(廖是聪), Jing-Hui Di(邸敬慧), Shuai Guo(郭帅), Ren-Jie Chen(陈仁杰), A-Ru Yan(闫阿儒), Lei Shi(石磊) Chin. Phys. B, 2020, 29 (5):  057501.  DOI: 10.1088/1674-1056/ab7b57 Abstract ( 802 )   HTML   PDF (572KB) ( 191 )   The Nd-Fe-B magnets are pre-sintered and then processed with hot-pressing, and the resulting magnets are called the hot-pressed pretreated (HPP) magnets. The coercivity of the HPP magnets increases as the annealed temperature increases. When the annealing temperature is 900℃, the coercivity of the magnet is only 17.6 kOe (1 Oe=79.5775 A·m-1), but when the annealing temperature rises up to 1060℃, the coercivity of the magnet reaches 23.53 kOe, which is remarkably increased by 33.7%. The microstructure analysis indicates that the grain surface of the HPP magnet becomes smoother as the annealed temperature increases. The microstructure factor α is changed according to the intrinsic coercivity model formula. The α of the magnet at 900℃ is only 0.578, but it is 0.825 at 1060℃. Microstructural optimization is due mainly to the increase of coercivity of the HPP magnet.

SPECIAL TOPIC—Topological 2D materials

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Magnetic field enhanced single particle tunneling in MoS2-superconductor vertical Josephson junction Wen-Zheng Xu(徐文正), Lai-Xiang Qin(秦来香), Xing-Guo Ye(叶兴国), Fang Lin(林芳), Da-Peng Yu(俞大鹏), Zhi-Min Liao(廖志敏) Chin. Phys. B, 2020, 29 (5):  057502.  DOI: 10.1088/1674-1056/ab8209 Abstract ( 837 )   HTML   PDF (726KB) ( 249 )   As a prototypical transition-metal dichalcogenide semiconductor, MoS2 possesses strong spin-orbit coupling, which provides an ideal platform for the realization of interesting physical phenomena. Here, we report the magnetotransport properties in NbN-MoS2-NbN sandwich junctions at low temperatures. Above the critical temperature around ～11 K, the junction resistance shows weak temperature dependence, indicating a tunneling behavior. While below ～11 K, nearly zero junction resistance is observed, indicating the superconducting state in the MoS2 layer induced by the superconducting proximity effect. When a perpendicular magnetic field ～1 T is applied, such proximity effect is suppressed, accompanying with insulator-like temperature-dependence of the junction resistance. Intriguingly, when further increasing the magnetic field, the junction conductance is significantly enhanced, which is related to the enhanced single particle tunneling induced by the decrease of the superconducting energy gap with increasing magnetic fields. In addition, the possible Majorana zero mode on the surface of MoS2 can further lead to the enhancement of the junction conductance.

RAPID COMMUNICATION

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Low temperature magnetism in the rare-earth perovskite GdScO3 Jie-Ming Sheng(盛洁明), Xu-Cai Kan(阚绪材), Han Ge(葛晗), Pei-Qian Yuan(袁培骞), Lei Zhang(张磊), Nan Zhao(赵南), Zong-Mei Song(宋宗美), Yuan-Yin Yao(姚远寅), Ji-Ning Tang(唐霁宁), Shan-Min Wang(王善民), Ming-Liang Tian(田明亮), Xin Tong(童欣), Liu-Suo Wu(吴留锁) Chin. Phys. B, 2020, 29 (5):  057503.  DOI: 10.1088/1674-1056/ab8200 Abstract ( 781 )   HTML   PDF (5034KB) ( 221 )   The magnetic phase diagram of rare-earth perovskite compound, GdScO3, has been investigated by magnetization and heat capacity. The system undergoes an antiferromagnetic phase transition at TN=2.6 K, with an easy axis of magnetization along the a axis. The magnetization measurements show that it exists a spin-flop transition around 0.3 T for the applied field along the a axis. The critical magnetic field for the antiferromagnetic-to-paramagnetic transition is near 3.2 T when temperature approaches zero. By scaling susceptibilities, we presume this point (B=3.2 T, T=0 K) might be a field-induced quantum critical point and the magnetic critical fluctuations can even be felt above TN.

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

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Microstructure and ferromagnetism of heavily Mn doped SiGe thin flims Hot! Huanming Wang(王焕明), Sen Sun(孙森), Jiayin Xu(徐家胤), Xiaowei Lv(吕晓伟), Yuan Wang(汪渊), Yong Peng(彭勇), Xi Zhang(张析), Gang Xiang(向钢) Chin. Phys. B, 2020, 29 (5):  057504.  DOI: 10.1088/1674-1056/ab8219 Abstract ( 746 )   HTML   PDF (3605KB) ( 269 )   Heavily Mn-doped SiGe thin films were grown by radio frequency magnetron sputtering and then treated by post-growth thermal annealing. Structural characterizations reveal the coexistence of Mn-diluted SiGe crystals and Mn-rich nanoclusters in the annealed films. Magnetic measurements indicate the ferromagnetic ordering of the annealed samples above room temperature . The data suggest that the ferromagnetism is probably mainly contributed by the Ge-rich nanoclusters and partially contributed by the tensile-strained Mn-diluted SiGe crystals. The results may be useful for room temperature spintronic applications based on group IV semiconductors.

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Role of the spin anisotropy of the interchain interaction in weakly coupled antiferromagnetic Heisenberg chains Hot! Yuchen Fan(樊宇辰), Rong Yu(俞榕) Chin. Phys. B, 2020, 29 (5):  057505.  DOI: 10.1088/1674-1056/ab820b Abstract ( 756 )   HTML   PDF (448KB) ( 232 )   In quasi-one-dimensional (q1D) quantum antiferromagnets, the complicated interplay of intrachain and interchain exchange couplings may give rise to rich phenomena. Motivated by recent progress on field-induced phase transitions in the q1D antiferromagnetic (AFM) compound YbAlO3, we study the phase diagram of spin-1/2 Heisenberg chains with Ising anisotropic interchain couplings under a longitudinal magnetic field via large-scale quantum Monte Carlo simulations, and investigate the role of the spin anisotropy of the interchain coupling on the ground state of the system. We find that the Ising anisotropy of the interchain coupling can significantly enhance the longitudinal spin correlations and drive the system to an incommensurate AFM phase at intermediate magnetic fields, which is understood as a longitudinal spin density wave (LSDW). With increasing field, the ground state changes to a canted AFM order with transverse spin correlations. We further provide a global phase diagram showing how the competition between the LSDW and the canted AFM states is tuned by the Ising anisotropy of the interchain coupling.

RAPID COMMUNICATION

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Tunable deconfined quantum criticality and interplay of different valence-bond solid phases Hot! Bowen Zhao(赵博文), Jun Takahashi, Anders W. Sandvik Chin. Phys. B, 2020, 29 (5):  057506.  DOI: 10.1088/1674-1056/ab889b Abstract ( 926 )   HTML   PDF (2704KB) ( 478 )   We use quantum Monte Carlo simulations to study an S=1/2 spin model with competing multi-spin interactions. We find a quantum phase transition between a columnar valence-bond solid (cVBS) and a Néel antiferromagnet (AFM), as in the scenario of deconfined quantum-critical points, as well as a transition between the AFM and a staggered valence-bond solid (sVBS). By continuously varying a parameter, the sVBS-AFM and AFM-cVBS boundaries merge into a direct sVBS-cVBS transition. Unlike previous models with putative deconfined AFM-cVBS transitions, e.g., the standard J-Q model, in our extended J-Q model with competing cVBS and sVBS inducing terms the transition can be tuned from continuous to first-order. We find the expected emergent U(1) symmetry of the microscopically Z4 symmetric cVBS order parameter when the transition is continuous. In contrast, when the transition changes to first-order, the clock-like Z4 fluctuations are absent and there is no emergent higher symmetry. We argue that the confined spinons in the sVBS phase are fracton-like. We also present results for an SU(3) symmetric model with a similar phase diagram. The new family of models can serve as a useful tool for further investigating open questions related to deconfined quantum criticality and its associated emergent symmetries.

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

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A novel diluted magnetic semiconductor (Ca,Na)(Zn,Mn)2Sb2 with decoupled charge and spin dopings Yilun Gu(顾轶伦), Haojie Zhang(张浩杰), Rufei Zhang(张茹菲), Licheng Fu(傅立承), Kai Wang(王恺), Guoxiang Zhi(智国翔), Shengli Guo(郭胜利), Fanlong Ning(宁凡龙) Chin. Phys. B, 2020, 29 (5):  057507.  DOI: 10.1088/1674-1056/ab892e Abstract ( 699 )   HTML   PDF (920KB) ( 129 )   We report the successful synthesis of a new diluted magnetic semiconductor (Ca,Na)(Zn,Mn)2Sb2. Na and Mn are doped into the parent compound CaZn2Sb2, which has the same crystal structure as that of "122" type iron-based superconductor CaFe2As2. Na substitution for Ca and Mn substitution for Zn introduce carriers and spins, respectively. Doping Mn atoms alone up to 5% does not induce any type of magnetic ordering. When both Na and Mn are co-doped, a ferromagnetic ordering with maximum TC～10 K has been observed. Iso-thermal magnetization shows that the coercive field is up to ～245 Oe at 2 K. Below TC, a negative magneto-resistance with MR ～12% has also been achieved.

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Variable-K double trenches SOI LDMOS with high-concentration P-pillar Lijuan Wu(吴丽娟), Lin Zhu(朱琳), Xing Chen(陈星) Chin. Phys. B, 2020, 29 (5):  057701.  DOI: 10.1088/1674-1056/ab7e94 Abstract ( 707 )   HTML   PDF (484KB) ( 135 )   A variable-K trenches silicon-on-insulator (SOI) lateral diffused metal-oxide-semiconductor field-effect transistor (MOSFET) with a double conductive channel is proposed based on the enhancement of low dielectric constant media to electric fields. The device features variable-K dielectric double trenches and a P-pillar between the trenches (VK DT-P LDMOS). The low-K dielectric layer on the surface increases electric field of it. Adding a variable-K material introduces a new electric field peak to the drift region, so as to optimize electric field inside the device. Introduction of the high-concentration vertical P-pillar between the two trenches effectively increases doping concentration of the drift region and maintains charge balance inside it. Thereby, breakdown voltage (BV) of the device is increased. The double conductive channels provide two current paths that significantly reduce specific on-resistance (Ron,sp). Simulation results demonstrate that a 17-μm-length device can achieve a BV of 554 V and a low on-resistance of 13.12 mΩ·cm2. The Ron,sp of VK DT-P LDMOS is reduced by 78.9% compared with the conventional structure.

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Effect of heating time on structural, morphology, optical, and photocatalytic properties of g-C3N4 nanosheets Nguyen Manh Hung, Le Thi Mai Oanh, Lam Thi Hang, Pham Do Chung, Pham Thi Duyen, Dao Viet Thang, Nguyen Van Minh Chin. Phys. B, 2020, 29 (5):  057801.  DOI: 10.1088/1674-1056/ab7e95 Abstract ( 664 )   HTML   PDF (903KB) ( 113 )   Effect of heating time on the structural, morphology, optical, and photocatalytic properties of graphitic carbon nitride (g-C3N4) nanosheets prepared at 550℃ in Ar atmosphere is studied. The investigations are carried out by using x-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), UV-vis absorption, and photoluminescence (PL). At a heating temperature of 550℃, g-C3N4 nanocrystals are formed after 0.5 h and become more orderly as the heating time increases. The surface area of the g-C3N4 nanosheets significantly increases as the preparation time increases. The g-C3N4 prepared in 2.5 h shows the highest photocatalytic performance, decomposing completely 10 ppm RhB solution under xenon lamp irradiation for 2.0 h.

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Extinction mechanisms of hyperbolic h-BN nanodisk Runkun Chen(陈闰堃), Jianing Chen(陈佳宁) Chin. Phys. B, 2020, 29 (5):  057802.  DOI: 10.1088/1674-1056/ab8898 Abstract ( 636 )   HTML   PDF (736KB) ( 184 )   We applied the finite element method to calculate the extinction spectrum of single hyperbolic hexagonal boron nitride (h-BN) nanodisk. We show that the hyperbolic h-BN nanodisk exhibits two extinction mechanisms in the mid-infrared region. The volume confined phonon polaritons resonances of the nanodisk give rise to a series of weak extinction peaks. The localized surface phonon polaritons lead to a robust dipolar extinction, and the extinction peak position is tunable by varying the size of the h-BN nanodisk. These findings reveal the mechanisms of the interaction between light and resonant h-BN nanodisk, which are essential for h-BN related opto-electromagnetic applications.

SPECIAL TOPIC—Terahertz physics

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Single-shot measurement of THz pulses Lei Yang(杨磊), Lei Hou(侯磊), Chengang Dong(董陈岗), Wei Shi(施卫) Chin. Phys. B, 2020, 29 (5):  057803.  DOI: 10.1088/1674-1056/ab821f Abstract ( 875 )   HTML   PDF (1116KB) ( 427 )   Terahertz (THz) waves have shown a broad prospect in the analysis of some dielectric materials because of their special properties. For the ultrafast irreversible processes, the THz single-shot measurement is a good choice. In this paper, a single-shot system is investigated, where a pump beam is used to generate THz pulses with high electrical field by optical rectification in LiNbO3, the probe beam with wavefront tilted by a blazed grating is used for single-shot measurement. The time window is up to 90 ps, the signal to noise ratio is 2000:1, the spectrum covers from 0.1 THz to about 2.0 THz, and the spectral resolution is 0.011 THz. The single-shot measurement result agrees well with that of a traditional electrical-optic sampling method.

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Insulator-metal transition in CaTiO3 quantum dots induced by ultrafast laser pulses Tong Liu(刘彤), Hong Zhang(张红), Xin-Lu Cheng(程新路) Chin. Phys. B, 2020, 29 (5):  058101.  DOI: 10.1088/1674-1056/ab7d9e Abstract ( 538 )   HTML   PDF (2581KB) ( 160 )   According to time-dependent density functional theory (TDDFT), we study the interactions between ultra-fast laser pulses and two kinds of calcium titanate quantum dots (PCTO-QDs and MCTO-QDs). Under the action of localized field effect, ultrafast laser can induce quantum dots to make the transition from insulator to metal. The PCTO-QDs are ultimately metallic, while the MCTO-QDs are still insulator after experiencing metal state. This is bacause the stability of the unsaturated atoms in the outermost layer of PCTO-QDs is weak and the geometric configuration of MCTO-QDs as a potential well will also reduce the damage of laser. Moreover, laser waveforms approaching to the intrinsic frequency of quantum dots tend to cause the highest electron levels to cross the Fermi surface. In this paper, it is reported that the insulating quantum dots can be transformed into metal by adjusting the intensity and frequency of laser. The importance of local morphology is emphasized by comparing two kinds of CTO-QDs. More importantly, it is an important step to identify the potential properties of perovskite materials.

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Influence of N+ implantation on structure, morphology, and corrosion behavior of Al in NaCl solution Hadi Savaloni, Rezvan Karami, Helma Sadat Bahari, Fateme Abdi Chin. Phys. B, 2020, 29 (5):  058102.  DOI: 10.1088/1674-1056/ab7d97 Abstract ( 618 )   HTML   PDF (3471KB) ( 369 )   Structural and morphological changes as well as corrosion behavior of N+ implanted Al in 0.6 M NaCl solution as function of N+ fluence are investigated. The x-ray diffraction results confirmed AlN formation. The atomic force microscope (AFM) images showed larger grains on the surface of Al with increasing N+ fluence. This can be due to the increased number of impacts of N+ with Al atoms and energy conversion to heat, which increases the diffusion rate of the incident ions in the target. Hence, the number of the grain boundaries is reduced, resulting in corrosion resistance enhancement. Electrochemical impedance spectroscopy (EIS) and polarization results showed the increase of corrosion resistance of Al with increasing N+ fluence. EIS data was used to simulate equivalent electric circuits (EC) for the samples. Strong dependence of the surface morphology on the EC elements was observed. The scanning electron microscope (SEM) analysis of the samples after corrosion test also showed that the surfaces of the implanted Al samples remain more intact relative to the untreated Al sample, consistent with the EIS and polarization results.

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Mg acceptor activation mechanism and hole transport characteristics in highly Mg-doped AlGaN alloys Qing-Jun Xu(徐庆君), Shi-Ying Zhang(张士英), Bin Liu(刘斌), Zhen-Hua Li(李振华), Tao Tao(陶涛), Zi-Li Xie(谢自力), Xiang-Qian Xiu(修向前), Dun-Jun Chen(陈敦军), Peng Chen(陈鹏), Ping Han(韩平), Ke Wang(王科), Rong Zhang(张荣), You-Liao Zheng(郑有炓) Chin. Phys. B, 2020, 29 (5):  058103.  DOI: 10.1088/1674-1056/ab7e93 Abstract ( 887 )   HTML   PDF (476KB) ( 197 )   The Mg acceptor activation mechanism and hole transport characteristics in AlGaN alloy with Mg doping concentration (～ 1020 cm-3) grown by metal-organic chemical vapor deposition (MOCVD) are systematically studied through optical and electrical properties. Emission lines of shallow oxygen donors and (VIII complex)1- as well as VN3+ and neutral Mg acceptors are observed, which indicate that self-compensation is occurred in Mg-doped AlGaN at highly doping levels. The fitting of the temperature-dependent Hall effect data shows that the acceptor activation energy values in Mg-doped AlxGa1-xN (x=0.23, 0.35) are 172 meV and 242 meV, and the hole concentrations at room temperature are 1.2×1018 cm-3 and 3.3×1017 cm-3, respectively. Therefore, it is believed that there exists the combined effect of the Coulomb potentials of the dopants and screening of the Coulomb potentials by a high hole concentration. Moreover, due to the high ionized acceptors' concentration and compensation ratio, the impurity conduction becomes more prominent and the valence band mobility drops sharply at low temperature.

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Prediction of structured void-containing 1T-PtTe2 monolayer with potential catalytic activity for hydrogen evolution reaction Bao Lei(雷宝), Yu-Yang Zhang(张余洋), Shi-Xuan Du(杜世萱) Chin. Phys. B, 2020, 29 (5):  058104.  DOI: 10.1088/1674-1056/ab8203 Abstract ( 595 )   HTML   PDF (796KB) ( 193 )   Two-dimensional (2D) transition metal dichalcogenides (TMDs) have attracted considerable attention because of their unique properties and great potential in nano-technology applications. Great efforts have been devoted to fabrication of novel structured TMD monolayers by modifying their pristine structures at the atomic level. Here we propose an intriguing structured 1T-PtTe2 monolayer as hydrogen evolution reaction (HER) catalyst, namely, Pt4Te7, using first-principles calculations. It is found that Pt4Te7 is a stable monolayer material verified by the calculation of formation energy, phonon dispersion, and ab initio molecular dynamics simulations. Remarkably, the novel structured void-containing monolayer exhibits superior catalytic activity toward HER compared with the pristine one, with a Gibbs free energy very close to zero (less than 0.07 eV). These features indicate that Pt4Te7 monolayer is a high-performance HER catalyst with a high platinum utilization. These findings open new perspectives for the functionalization of 2D TMD materials at an atomic level and its application in HER catalysis.

SPECIAL TOPIC—Active matters physics

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Constraint dependence of average potential energy of a passive particle in an active bath Simin Ye(叶思敏), Peng Liu(刘鹏), Zixuan Wei(魏子轩), Fangfu Ye(叶方富), Mingcheng Yang(杨明成), Ke Chen(陈科) Chin. Phys. B, 2020, 29 (5):  058201.  DOI: 10.1088/1674-1056/ab7d9b Abstract ( 852 )   HTML   PDF (624KB) ( 304 )   We quantify the mean potential energy of a passive colloidal particle harmonically confined in a bacterial solution using optical traps. We find that the average potential energy of the passive particle depends on the trap stiffness, in contrast to the equilibrium case where energy partition is independent of the external constraints. The constraint dependence of the mean potential energy originates from the fact that the persistent collisions between the passive particle and the active bacteria are influenced by the particle relaxation dynamics. Our experimental results are consistent with the Brownian dynamics simulations, and confirm the recent theoretical prediction.

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Relationship between ESIPT properties and antioxidant activities of 5-hydroxyflavone derivates Chaofan Sun(孙朝范), Bifa Cao(曹必发), Hang Yin(尹航), Ying Shi(石英) Chin. Phys. B, 2020, 29 (5):  058202.  DOI: 10.1088/1674-1056/ab7ea1 Abstract ( 644 )   HTML   PDF (772KB) ( 356 )   It is of great significance to study the relationship between the excited state intramolecular proton transfer (ESIPT) properties and antioxidant activities of compounds in the field of life sciences. In this work, two novel compounds 5HF-OMe and 5HF-NH2 are designed through introducing a methoxy- and amino-group into the structure of 5-hydroxyflavone (5HF) respectively. The relationship between the ESIPT reaction and antioxidant activities of the three compounds is studied via the density functional theory (DFT) and time-dependent DFT (TD-DFT) methods. The calculated potential energy curves suggest that the rate of ESIPT reaction will gradually slow down from 5HF to 5HF-OMe and 5HF-NH2. In addition, the antioxidant activities of the three compounds gradually enhance from 5HF to 5HF-OMe and 5HF-NH2, which can be seen from the calculated energy gaps and ionization potential values. Interestingly, the above results imply that the rate of ESIPT reaction has a negative relationship with the antioxidant activities of the compounds, i.e., the slower rate of ESIPT reaction will reflect the higher antioxidant activity of the compound, which will provide valuable reference for detecting the antioxidant activity of compound via the photophysical method.

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Characteristic enhancement in tunnel field-effect transistors via introduction of vertical graded source Zhijun Lyu(吕智军), Hongliang Lu(吕红亮), Yuming Zhang(张玉明), Yimen Zhang(张义门), Bin Lu(芦宾), Yi Zhu(朱翊), Fankang Meng(孟凡康), Jiale Sun(孙佳乐) Chin. Phys. B, 2020, 29 (5):  058501.  DOI: 10.1088/1674-1056/ab7d99 Abstract ( 685 )   HTML   PDF (606KB) ( 125 )   A novel vertical graded source tunnel field-effect transistor (VGS-TFET) is proposed to improve device performance. By introducing a source with linearly graded component, the on-state current increases by more than two decades higher than that of the conventional GaAs TFETs without sacrificing the subthreshold swing (SS) due to the improved band-to-band tunneling efficiency. Compared with the conventional TFETs, much larger drive current range can be achieved by the proposed VGS-TFET with SS below the thermionic limitation of 60 mV/dec. Furthermore, the minimum SS about 20 mV/dec indicates its promising potential for further ultralow power applications.

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Multistability and coexisting transient chaos in a simple memcapacitive system Fu-Ping Wang(王富平), Fa-Qiang Wang(王发强) Chin. Phys. B, 2020, 29 (5):  058502.  DOI: 10.1088/1674-1056/ab7e98 Abstract ( 615 )   HTML   PDF (7246KB) ( 292 )   The self-excited attractors and hidden attractors in a memcapacitive system which has three elements are studied in this paper. The critical parameter of stable and unstable states is calculated by identifying the eigenvalues of Jacobian matrix. Besides, complex dynamical behaviors are investigated in the system, such as coexisting attractors, hidden attractors, coexisting bifurcation modes, intermittent chaos, and multistability. From the theoretical analyses and numerical simulations, it is found that there are four different kinds of transient transition behaviors in the memcapacitive system. Finally, field programmable gate array (FPGA) is used to implement the proposed chaotic system.

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High-performance inverters based on ambipolar organic-inorganic heterojunction thin-film transistors Sheng Sun(孙圣), Yuzhi Li(李育智), Shengdong Zhang(张盛东) Chin. Phys. B, 2020, 29 (5):  058503.  DOI: 10.1088/1674-1056/ab7e96 Abstract ( 719 )   HTML   PDF (757KB) ( 113 )   This work reports on the integration of organic and inorganic semiconductors as heterojunction active layers for high-performance ambipolar transistors and complementary metal-oxide-semiconductor (CMOS)-like inverters. Pentacene is employed as a p-type organic semiconductor for its stable electrical performance, while the solution-processed scandium (Sc) substituted indium oxide (ScInO) is employed as an n-type inorganic semiconductor. It is observed that by regulating the doping concentration of Sc, the electrical performance of the n-type semiconductor could be well controlled to obtain a balance with the electrical performance of the p-type semiconductor, which is vital for achieving high-performance inverters. When the doping concentration of Sc is 10 at.%, the CMOS-like logic inverters exhibit a voltage gain larger than 80 and a wide noise margin (53% of the theoretical value). The inverters also respond well to the input signal with frequency up to 500 Hz.

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Ultraviolet irradiation dosimeter based on persistent photoconductivity effect of ZnO Chao-Jun Wang(王朝骏), Xun Yang(杨珣), Jin-Hao Zang(臧金浩), Yan-Cheng Chen(陈彦成), Chao-Nan Lin(林超男), Zhong-Xia Liu(刘忠侠), Chong-Xin Shan(单崇新) Chin. Phys. B, 2020, 29 (5):  058504.  DOI: 10.1088/1674-1056/ab8891 Abstract ( 657 )   HTML   PDF (1576KB) ( 150 )   It is essential to determine the accumulative ultraviolet (UV) irradiation over a period of time in some cases, such as monitoring UV irradiation to the skin, solar disinfection of water, photoresist exposure, etc. UV colorimetric dosimeters, which use dyes' color change to monitor the amount of UV exposure, have been widely studied. However, the exposure data of these UV colorimetric dosimeters can hardly be converted to digital signals, limiting their applications. In this paper, a UV dosimeter has been proposed and demonstrated based on the persistent photoconductivity (PPC) in zinc oxide microwires (ZnO MWs). The PPC effect usually results in high photoconductivity gain but low response speed, which has been regarded as a disadvantage for photodetectors. However, in this work, the unique characteristics of the PPC effect have been utilized to monitoring the accumulative exposure. We demonstrate that the photocurrent in the ZnO MWs depends on the accumulative UV exposure due to the PPC effect, thus the photocurrent can be utilized to determine the UV accumulation. The dosimeter is immune to visible light and exhibits a photoconductive gain of 2654, and the relative error of the dosimeter is about 10%. This UV dosimeter with electrical output is reusable and convenient to integrate with other electronic devices and may also open a new application area for the PPC effect.

SPECIAL TOPIC—Terahertz physics

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Noise temperature distribution of superconducting hot electron bolometer mixers Kang-Min Zhou(周康敏), Wei Miao(缪巍), Yue Geng(耿悦), Yan Delorme, Wen Zhang(张文), Yuan Ren(任远), Kun Zhang(张坤), Sheng-Cai Shi(史生才) Chin. Phys. B, 2020, 29 (5):  058505.  DOI: 10.1088/1674-1056/ab81f9 Abstract ( 770 )   HTML   PDF (3142KB) ( 210 )   We report on the investigation of optimal bias region of a wide-band superconducting hot electron bolometer (HEB) mixer in terms of noise temperature performance for multi-pixel heterodyne receiver application in the 5-meter Dome A Terahertz Explorer (DATE5) telescope. By evaluating the double sideband (DSB) receiver noise temperature (Trec) across a wide frequency range from 0.2 THz to 1.34 THz and with a large number of bias points, a broad optimal bias region has been observed, illustrating a good bias applicability for multipixel application since the performance of the HEB mixer is uniquely determined by each bias point. The noise temperature of the HEB mixer has been analyzed by calibrating the noise contribution of all RF components, whose transmissions have been measured by a time-domain spectroscopy. The corrected noise temperature distribution shows a frequency independence relation. The dependence of the optimal bias region on the bath temperature of the HEB mixer has also been investigated, the bath temperature has limited effect on the lowest receiver noise temperature until 7 K, however the optimal bias region deteriorates obviously with increasing bath temperature.

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Generating mechanism of pathological beta oscillations in STN-GPe circuit model: A bifurcation study Jing-Jing Wang(王静静), Yang Yao(姚洋), Zhi-Wei Gao(高志伟), Xiao-Li Li(李小俚), Jun-Song Wang(王俊松) Chin. Phys. B, 2020, 29 (5):  058701.  DOI: 10.1088/1674-1056/ab7e9b Abstract ( 587 )   HTML   PDF (705KB) ( 155 )   Parkinson's disease (PD) is characterized by pathological spontaneous beta oscillations (13 Hz-35 Hz) often observed in basal ganglia (BG) composed of subthalamic nucleus (STN) and globus pallidus (GPe) populations. From the viewpoint of dynamics, the spontaneous oscillations are related to limit cycle oscillations in a nonlinear system; here we employ the bifurcation analysis method to elucidate the generating mechanism of the pathological spontaneous beta oscillations underlined by coupling strengths and intrinsic properties of the STN-GPe circuit model. The results reveal that the increase of inter-coupling strength between STN and GPe populations induces the beta oscillations to be generated spontaneously, and causes the oscillation frequency to decrease. However, the increase of intra-coupling (self-feedback) strength of GPe can prevent the model from generating the oscillations, and dramatically increase the oscillation frequency. We further provide a theoretical explanation for the role played by the inter-coupling strength of GPe population in the generation and regulation of the oscillations. Furthermore, our study reveals that the intra-coupling strength of the GPe population provides a switching mechanism on the generation of the abnormal beta oscillations: for small value of the intra-coupling strength, STN population plays a dominant role in inducing the beta oscillations; while for its large value, the GPe population mainly determines the generation of this oscillation.

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Current improvement in substrate structured Sb2S3 solar cells with MoSe2 interlayer Lu Liu(刘璐), Sheng-Li Zhang(张生利), Jian-Yu Wu(吴建宇), Wei-Huang Wang(王伟煌), Wei Liu(刘玮), Li Wu(武莉), Yi Zhang(张毅) Chin. Phys. B, 2020, 29 (5):  058801.  DOI: 10.1088/1674-1056/ab8220 Abstract ( 611 )   HTML   PDF (1523KB) ( 260 )   Sb2S3 solar cells with substrate structure usually suffer from pretty low short circuit current (JSC) due to the defects and poor carrier transport. The Sb2S3, as a one-dimensional material, exhibits orientation-dependent carrier transport property. In this work, a thin MoSe2 layer is directly synthesized on the Mo substrate followed by depositing the Sb2S3 thin film. The x-ray diffraction (XRD) patterns confirm that a thin MoSe2 layer can improve the crystallization of the Sb2S3 film and induce (hk1) orientations, which can provide more carrier transport channels. Kelvin probe force microscopy (KPFM) results suggest that this modified Sb2S3 film has a benign surface with less defects and dangling bonds. The variation of the surface potential of Sb2S3 indicates a much more efficient carrier separation. Consequently, the power conversion efficiency (PCE) of the substrate structured Sb2S3 thin film solar cell is improved from 1.36% to 1.86%, which is the best efficiency of the substrate structured Sb2S3 thin film solar cell, and JSC significantly increases to 13.6 mA/cm2. According to the external quantum efficiency (EQE) and C-V measurements, the modified crystallization and elevated built-in electric field are the main causes.

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Asynchronism of the spreading dynamics underlying the bursty pattern Tong Wang(王童), Ming-Yang Zhou(周明洋), Zhong-Qian Fu(付忠谦) Chin. Phys. B, 2020, 29 (5):  058901.  DOI: 10.1088/1674-1056/ab81fe Abstract ( 559 )   HTML   PDF (464KB) ( 191 )   The potential mechanisms of the spreading phenomena uncover the organizations and functions of various systems. However, due to the lack of valid data, most of early works are limited to the simulated process on model networks. In this paper, we track and analyze the propagation paths of real spreading events on two social networks: Twitter and Brightkite. The empirical analysis reveals that the spreading probability and the spreading velocity present the explosive growth within a short period, where the spreading probability measures the transferring likelihood between two neighboring nodes, and the spreading velocity is the growth rate of the information in the whole network. Besides, we observe the asynchronism between the spreading probability and the spreading velocity. To explain the interesting and abnormal issue, we introduce the time-varying spreading probability into the susceptible-infected (SI) and linear threshold (LT) models. Both the analytic and experimental results reproduce the spreading phenomenon in real networks, which deepens our understandings of spreading problems.