Table of contents

18 May 2021, Volume 30 Issue 6 Previous issue    Next issue

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GENERAL

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Exact explicit solitary wave and periodic wave solutions and their dynamical behaviors for the Schamel-Korteweg-de Vries equation Bin He(何斌) and Qing Meng(蒙清) Chin. Phys. B, 2021, 30 (6):  060201.  DOI: 10.1088/1674-1056/abd7d1 Abstract ( 446 )   HTML ( 3 )   PDF (5141KB) ( 108 )   The Schamel-Korteweg-de Vries equation is investigated by the approach of dynamics. The existences of solitary wave including ω-shape solitary wave and periodic wave are proved via investigating the dynamical behaviors with phase space analyses. The sufficient conditions to guarantee the existences of the above solutions in different regions of the parametric space are given. All possible exact explicit parametric representations of the waves are also presented. Along with the details of the analyses, the analytical results are numerically simulated lastly.

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Soliton, breather, and rogue wave solutions for solving the nonlinear Schrödinger equation using a deep learning method with physical constraints Jun-Cai Pu(蒲俊才), Jun Li(李军), and Yong Chen(陈勇) Chin. Phys. B, 2021, 30 (6):  060202.  DOI: 10.1088/1674-1056/abd7e3 Abstract ( 763 )   HTML ( 4 )   PDF (2798KB) ( 275 )   The nonlinear Schrödinger equation is a classical integrable equation which contains plenty of significant properties and occurs in many physical areas. However, due to the difficulty of solving this equation, in particular in high dimensions, lots of methods are proposed to effectively obtain different kinds of solutions, such as neural networks among others. Recently, a method where some underlying physical laws are embeded into a conventional neural network is proposed to uncover the equation's dynamical behaviors from spatiotemporal data directly. Compared with traditional neural networks, this method can obtain remarkably accurate solution with extraordinarily less data. Meanwhile, this method also provides a better physical explanation and generalization. In this paper, based on the above method, we present an improved deep learning method to recover the soliton solutions, breather solution, and rogue wave solutions of the nonlinear Schrödinger equation. In particular, the dynamical behaviors and error analysis about the one-order and two-order rogue waves of nonlinear integrable equations are revealed by the deep neural network with physical constraints for the first time. Moreover, the effects of different numbers of initial points sampled, collocation points sampled, network layers, neurons per hidden layer on the one-order rogue wave dynamics of this equation have been considered with the help of the control variable way under the same initial and boundary conditions. Numerical experiments show that the dynamical behaviors of soliton solutions, breather solution, and rogue wave solutions of the integrable nonlinear Schrödinger equation can be well reconstructed by utilizing this physically-constrained deep learning method.

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$\mathcal{H}_{\infty }$ state estimation for Markov jump neural networks with transition probabilities subject to the persistent dwell-time switching rule Hao Shen(沈浩), Jia-Cheng Wu(吴佳成), Jian-Wei Xia(夏建伟), and Zhen Wang(王震) Chin. Phys. B, 2021, 30 (6):  060203.  DOI: 10.1088/1674-1056/abd7da Abstract ( 488 )   HTML ( 1 )   PDF (798KB) ( 114 )   We investigate the problem of $\mathcal{H}_{\infty}$ state estimation for discrete-time Markov jump neural networks. The transition probabilities of the Markov chain are assumed to be piecewise time-varying, and the persistent dwell-time switching rule, as a more general switching rule, is adopted to describe this variation characteristic. Afterwards, based on the classical Lyapunov stability theory, a Lyapunov function is established, in which the information about the Markov jump feature of the system mode and the persistent dwell-time switching of the transition probabilities is considered simultaneously. Furthermore, via using the stochastic analysis method and some advanced matrix transformation techniques, some sufficient conditions are obtained such that the estimation error system is mean-square exponentially stable with an $\mathcal{H}_{\infty}$ performance level, from which the specific form of the estimator can be obtained. Finally, the rationality and effectiveness of the obtained results are verified by a numerical example.

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Effect of symmetrical frequency chirp on pair production Kun Wang(王焜), Xuehua Hu(胡学华), Sayipjamal Dulat, and Bai-Song Xie(谢柏松) Chin. Phys. B, 2021, 30 (6):  060204.  DOI: 10.1088/1674-1056/abeee8 Abstract ( 493 )   HTML ( 2 )   PDF (10142KB) ( 194 )   By using Dirac-Heisenberg-Wigner formalism we study electron-positron pair production for linear, elliptic, nearly circular, and circular polarizations of electric fields with symmetrical frequency chirp, and we obtain momentum spectra and pair yield. The difference of results among polarized fields is obvious for the small chirp. When the chirp parameter increases, the momentum spectra tend to exhibit the multiphoton pair generation that is characterized by the multi-concentric ring structure. The increase of the number density is also remarkable compared to the case of asymmetrical frequency chirp. Note that the dynamically assisted Schwinger mechanism plays an important role for the enhanced pair production in the symmetrical frequency chirp.

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Entanglement properties of GHZ and W superposition state and its decayed states Xin-Feng Jin(金鑫锋), Li-Zhen Jiang(蒋丽珍), and Xiao-Yu Chen(陈小余) Chin. Phys. B, 2021, 30 (6):  060301.  DOI: 10.1088/1674-1056/abd74e Abstract ( 637 )   HTML ( 4 )   PDF (594KB) ( 96 )   We use the generalized Wootters formula, the positive partial transpose (PPT) criterion and the matched entanglement witness, to detect entanglement of three-qubit GHZ and W superposition state and its decayed states. It shows that the results of the generalized Wootters formula in the part near the W state are tight. In the other parts, the PPT criterion is superior to the generalized Wootters formula. Furthermore, we investigate the relationship between entanglement and coherence.

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Lie transformation on shortcut to adiabaticity in parametric driving quantum systems Jian-Jian Cheng(程剑剑), Yao Du(杜瑶), and Lin Zhang(张林) Chin. Phys. B, 2021, 30 (6):  060302.  DOI: 10.1088/1674-1056/abd747 Abstract ( 571 )   HTML ( 1 )   PDF (534KB) ( 211 )   Shortcut to adiabaticity (STA) is a speedway to produce the same final state that would result in an adiabatic, infinitely slow process. Two typical techniques to engineer STA are developed by either introducing auxiliary counterdiabatic fields or finding new Hamiltonians that own dynamical invariants to constraint the system into the adiabatic paths. In this paper, an efficient method is introduced to naturally cover the above two techniques with a unified Lie algebraic framework and neatly remove the design difficulties and loose assumptions in the two techniques. A general STA scheme for different potential expansions concisely achieves with the aid of squeezing transformations.

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Controlled quantum teleportation of an unknown single-qutrit state in noisy channels with memory Shexiang Jiang(蒋社想), Bao Zhao(赵宝), and Xingzhu Liang(梁兴柱) Chin. Phys. B, 2021, 30 (6):  060303.  DOI: 10.1088/1674-1056/abea95 Abstract ( 675 )   HTML ( 3 )   PDF (940KB) ( 118 )   This paper proposes a three-dimensional (3D) controlled quantum teleportation scheme for an unknown single-qutrit state. The scheme is first introduced in an ideal environment, and its detailed implementation is described via the transformation of the quantum system. Four types of 3D-Pauli-like noise corresponding to Weyl operators are created by Kraus operators:trit-flip, t-phase-flip, trit-phase-flip, and t-depolarizing. Then, this scheme is analyzed in terms of four types of noisy channel with memory. For each type of noise, the average fidelity is calculated as a function of memory and noise parameters, which is afterwards compared with classical fidelity. The results demonstrate that for trit-flip and t-depolarizing noises, memory will increase the average fidelity regardless of the noise parameter. However, for t-phase-flip and trit-phase-flip noises, memory may become ineffective in increasing the average fidelity above a certain noise threshold.

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Continuous-variable quantum key distribution based on photon addition operation Xiao-Ting Chen(陈小婷), Lu-Ping Zhang(张露萍), Shou-Kang Chang(常守康), Huan Zhang(张欢), and Li-Yun Hu(胡利云) Chin. Phys. B, 2021, 30 (6):  060304.  DOI: 10.1088/1674-1056/abd931 Abstract ( 596 )   HTML ( 1 )   PDF (980KB) ( 140 )   It is shown that the non-Gaussian operations can not only be used to prepare the nonclassical states, but also to improve the entanglement degree between Gaussian states. Thus these operations are naturally considered to enhance the performance of continuous variable quantum key distribution (CVQKD), in which the non-Gaussian operations are usually placed on the right-side of the entangled source. Here we propose another scheme for further improving the performance of CVQKD with the entangled-based scheme by operating photon-addition operation on the left-side of the entangled source. It is found that the photon-addition operation on the left-side presents both higher success probability and better secure key rate and transmission distance than the photon subtraction on the right-side, although they share the same maximal tolerable noise. In addition, compared to both photon subtraction and photon addition on the right-side, our scheme shows the best performance and the photon addition on the right-side is the worst.

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Practical decoy-state BB84 quantum key distribution with quantum memory Xian-Ke Li(李咸柯), Xiao-Qian Song(宋小谦), Qi-Wei Guo(郭其伟), Xing-Yu Zhou(周星宇), and Qin Wang(王琴) Chin. Phys. B, 2021, 30 (6):  060305.  DOI: 10.1088/1674-1056/abda31 Abstract ( 810 )   HTML ( 4 )   PDF (509KB) ( 176 )   We generalize BB84 quantum key distribution (QKD) to the scenario where the receiver adopts a heralded quantum memory (QM). With the heralded QM, the valid dark count rate of the receiver's single photon detectors can be mitigated obviously, which will lower the quantum bit error rate, and thus improve the performance of decoy-state BB84 QKD systems in long distance range. Simulation results show that, with practical experimental system parameters, decoy-state BB84 QKD with QM can exhibit performance comparable to that of without QM in short distance range, and exhibit performance better than that without QM in long distance range.

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Superfluid states in α-T3 lattice Yu-Rong Wu(吴玉容) and Yi-Cai Zhang(张义财) Chin. Phys. B, 2021, 30 (6):  060306.  DOI: 10.1088/1674-1056/abea8a Abstract ( 469 )   HTML ( 1 )   PDF (2482KB) ( 172 )   The superfluid states of attractive Hubbard model in α-T3 lattice are investigated. It is found that one usual needs three non-zero superfluid order parameters to describe the superfluid states due to three sublattices. When two hopping amplitudes are equal, the system has particle-hole symmetry. The flat band plays an important role in superfluid pairing near half filling. For example, when the filling factor falls into the flat band, the large density of states in the flat band favors superfluid pairing and the superfluid order parameters reach relatively large values. When the filling factor is in the gap between the flat band and upper band, the superfluid order parameters take small values due to the vanishing of density of states. The superfluid order parameters show nonmonotonic behaviors with the increase of filling factor. At last, we also investigate the edge states with open boundary conditions. It is shown that there exist some interesting edge states in the middle of quasi-particle bands.

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Dynamical stability of dipolar condensate in a parametrically modulated one-dimensional optical lattice Ji-Li Ma(马吉利), Xiao-Xun Li(李晓旬), Rui-Jin Cheng(程瑞锦), Ai-Xia Zhang(张爱霞), and Ju-Kui Xue(薛具奎) Chin. Phys. B, 2021, 30 (6):  060307.  DOI: 10.1088/1674-1056/abd746 Abstract ( 530 )   HTML ( 0 )   PDF (1538KB) ( 103 )   We study the stabilization properties of dipolar Bose-Einstein condensate in a deep one-dimensional optical lattice with an additional external parametrically modulated harmonic trap potential. Through both analytical and numerical methods, we solve a dimensionless nonlocal nonlinear discrete Gross-Pitaevskii equation with both the short-range contact interaction and the long-range dipole-dipole interaction. It is shown that, the stability of dipolar condensate in modulated deep optical lattice can be controled by coupled effects of the contact interaction, the dipolar interaction and the external modulation. The system can be stabilized when the dipolar interaction, the contact interaction, the average strength of potential and the ratio of amplitude to frequency of the modulation satisfy a critical condition. In addition, the breather state, the diffused state and the attractive-interaction-induced-trapped state are predicted. The dipolar interaction and the external modulation of the lattice play important roles in stabilizing the condensate.

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Transport properties of Tl2Ba2CaCu2O8 microbridges on a low-angle step substrate Sheng-Hui Zhao(赵生辉), Wang-Hao Tian(田王昊), Xue-Lian Liang(梁雪连), Ze He(何泽), Pei Wang(王培), Lu Ji(季鲁), Ming He(何明), and Hua-Bing Wang(王华兵) Chin. Phys. B, 2021, 30 (6):  060308.  DOI: 10.1088/1674-1056/abec35 Abstract ( 504 )   HTML ( 2 )   PDF (1575KB) ( 185 )   Tl-based superconducting devices have been drawn much attention for their high transition temperature (Tc), which allow the high temperature superconductors (HTS) devices to operate at temperature near 100 K. The realization of Tl-based devices will promote the research and application of HTS devices. In this work, we present transport properties of Tl2Ba2CaCu2O8 (Tl-2212) microbridges across a low-angle step on LaAlO3 (LAO) substrate. We experimentally demonstrate intrinsic Josephson effects (IJEs) in Tl-2212 films by tailoring the geometry, i.e., reducing the width of the microbridges. In the case of a 1 μm width microbridge, in addition to the observation of voltage branches and remarkable hysteresis on the current-voltage (I-V) characteristics, the temperature dependence of differential resistance shows a finite resistance above 60 K when the bias current is below the critical current. For comparison, the wider microbridges are also investigated, exhibiting a highly critical current but do not showing obvious IJEs.

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Wave packet dynamics of nonlinear Gazeau-Klauder coherent states of a position-dependent mass system in a Coulomb-like potential Faustin Blaise Migueu, Mercel Vubangsi, Martin Tchoffo, and Lukong Cornelius Fai Chin. Phys. B, 2021, 30 (6):  060309.  DOI: 10.1088/1674-1056/abd7e2 Abstract ( 393 )   HTML ( 1 )   PDF (1054KB) ( 77 )   A D=1 position-dependent mass approach to constructing nonlinear quantum states for a modified Coulomb potential is used to generate Gazeau-Klauder coherent states. It appears that their energy eigenvalues are scaled down by the quantum number and the nonlinearity coefficient. We study the basic properties of these states, which are found to be undefined on the whole complex plane, and some details of their revival structure are discussed.

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Dynamics of bright soliton in a spin-orbit coupled spin-1 Bose-Einstein condensate Hui Guo(郭慧), Xu Qiu(邱旭), Yan Ma(马燕), Hai-Feng Jiang(姜海峰), and Xiao-Fei Zhang(张晓斐) Chin. Phys. B, 2021, 30 (6):  060310.  DOI: 10.1088/1674-1056/abf34a Abstract ( 518 )   HTML ( 3 )   PDF (743KB) ( 248 )   We have investigated the dynamics of bright solitons in a spin-orbit coupled spin-1 Bose-Einstein condensate analytically and numerically. By using the hyperbolic sine function as the trial function to describe a plane wave bright soliton with a single finite momentum, we have derived the motion equations of soliton's spin and center of mass, and obtained its exact analytical solutions. Our results show that the spin-orbit coupling couples the soliton's spin with its center-of-mass motion, the spin oscillations induced by the exchange of atoms between components result in the periodical oscillation of center-of-mass, and the motion of center of mass of soliton can be viewed as a superposition of periodical and linear motions. Our analytical results have also been confirmed by the direct numerical simulations of Gross-Pitaevskii equations.

TOPICAL REVIEW—Quantum computation and quantum simulation

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Quantum computation and simulation with vibrational modes of trapped ions Wentao Chen(陈文涛), Jaren Gan, Jing-Ning Zhang(张静宁), Dzmitry Matuskevich, and Kihwan Kim(金奇奂) Chin. Phys. B, 2021, 30 (6):  060311.  DOI: 10.1088/1674-1056/ac01e3 Abstract ( 980 )   HTML ( 7 )   PDF (5874KB) ( 450 )   Vibrational degrees of freedom in trapped-ion systems have recently been gaining attention as a quantum resource, beyond the role as a mediator for entangling quantum operations on internal degrees of freedom, because of the large available Hilbert space. The vibrational modes can be represented as quantum harmonic oscillators and thus offer a Hilbert space with infinite dimensions. Here we review recent theoretical and experimental progress in the coherent manipulation of the vibrational modes, including bosonic encoding schemes in quantum information, reliable and efficient measurement techniques, and quantum operations that allow various quantum simulations and quantum computation algorithms. We describe experiments using the vibrational modes, including the preparation of non-classical states, molecular vibronic sampling, and applications in quantum thermodynamics. We finally discuss the potential prospects and challenges of trapped-ion vibrational-mode quantum information processing.

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Quantum computation and error correction based on continuous variable cluster states Shuhong Hao(郝树宏), Xiaowei Deng(邓晓玮), Yang Liu(刘阳), Xiaolong Su(苏晓龙), Changde Xie(谢常德), and Kunchi Peng(彭堃墀) Chin. Phys. B, 2021, 30 (6):  060312.  DOI: 10.1088/1674-1056/abeb0a Abstract ( 611 )   HTML ( 4 )   PDF (1213KB) ( 478 )   Measurement-based quantum computation with continuous variables, which realizes computation by performing measurement and feedforward of measurement results on a large scale Gaussian cluster state, provides a feasible way to implement quantum computation. Quantum error correction is an essential procedure to protect quantum information in quantum computation and quantum communication. In this review, we briefly introduce the progress of measurement-based quantum computation and quantum error correction with continuous variables based on Gaussian cluster states. We also discuss the challenges in the fault-tolerant measurement-based quantum computation with continuous variables.

SPECIAL TOPIC—Quantum computation and quantum simulation

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Fabrication of microresonators by using photoresist developer as etchant Shu-Qing Song(宋树清), Jian-Wen Xu(徐建文), Zhi-Kun Han(韩志坤), Xiao-Pei Yang(杨晓沛), Yu-Ting Sun(孙宇霆), Xiao-Han Wang(王晓晗), Shao-Xiong Li(李邵雄), Dong Lan(兰栋), Jie Zhao(赵杰), Xin-Sheng Tan(谭新生), and Yang Yu(于扬) Chin. Phys. B, 2021, 30 (6):  060313.  DOI: 10.1088/1674-1056/abf112 Abstract ( 662 )   HTML ( 3 )   PDF (1338KB) ( 317 )   In superconducting circuit, microwave resonators and capacitors are crucial components, and their quality has a strong impact on circuit performance. Here we develop a novel wet etching process to define these two components using common photoresist developer as etchant. This method reduces subsequent steps and can be completed immediately after development. By measuring the internal quality factor of resonators, we show that it is possible to achieve similar or better performance when compared with samples made by standard etching processes. This easy-to-implement method may boost the yield hence providing an alternative fabrication process for microwave resonators and capacitors.

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Interaction induced non-reciprocal three-level quantum transport Sai Li(李赛), Tao Chen(陈涛), Jia Liu(刘佳), and Zheng-Yuan Xue(薛正远) Chin. Phys. B, 2021, 30 (6):  060314.  DOI: 10.1088/1674-1056/abee0c Abstract ( 488 )   HTML ( 3 )   PDF (699KB) ( 199 )   Besides its fundamental importance, non-reciprocity has also found many potential applications in quantum technology. Recently, many quantum systems have been proposed to realize non-reciprocity, but stable non-reciprocal process is still experimentally difficult in general, due to the needed cyclical interactions in artificial systems or operational difficulties in solid state materials. Here, we propose a new kind of interaction induced non-reciprocal operation, based on the conventional stimulated-Raman-adiabatic-passage (STIRAP) setup, which removes the experimental difficulty of requiring cyclical interaction, and thus it is directly implementable in various quantum systems. Furthermore, we also illustrate our proposal on a chain of three coupled superconducting transmons, which can lead to a non-reciprocal circulator with high fidelity without a ring coupling configuration as in the previous schemes or implementations. Therefore, our protocol provides a promising way to explore fundamental non-reciprocal quantum physics as well as realize non-reciprocal quantum device.

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Fine-grained uncertainty relation for open quantum system Shang-Bin Han(韩尚斌), Shuai-Jie Li(李帅杰), Jing-Jun Zhang(张精俊), and Jun Feng(冯俊) Chin. Phys. B, 2021, 30 (6):  060315.  DOI: 10.1088/1674-1056/abf3b5 Abstract ( 621 )   HTML ( 1 )   PDF (1021KB) ( 181 )   The fine-grained uncertainty relation (FUR) is investigated for accelerating open quantum system, which manifests the celebrated Unruh effect, a crucial piece of the jigsaw for combining relativity and quantum physics. For a single detector, we show that the inevitable Unruh decoherence can induce a smaller FUR uncertainty bound, which indicates an additional measurement uncertainty may exist. For an open system combined with two detectors, via a nonlocal retrieval game, the related FUR uncertainty bound is determined by the non-classical correlation of the system. By estimating the maximal violation of Bell inequality for an accelerating system, we show that the FUR uncertainty bound can be protected from Unruh decoherence, due to quantum correlation generated through Markovian dynamics.

GENERAL

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Stationary response of colored noise excited vibro-impact system Jian-Long Wang(王剑龙), Xiao-Lei Leng(冷小磊), and Xian-Bin Liu(刘先斌) Chin. Phys. B, 2021, 30 (6):  060501.  DOI: 10.1088/1674-1056/abf12a Abstract ( 519 )   HTML ( 2 )   PDF (928KB) ( 60 )   The generalized cell mapping (GCM) method is used to obtain the stationary response of a single-degree-of-freedom. Vibro-impact system under a colored noise excitation. In order to show the advantage of the GCM method, the stochastic averaging method is also presented. Both of the two methods are tested through concrete examples and verified by the direct numerical simulation. It is shown that the GCM method can well predict the stationary response of this noise-perturbed system no matter whether the noise is wide-band or narrow-band, while the stochastic averaging method is valid only for the wide-band noise.

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Collective stochastic resonance behaviors of two coupled harmonic oscillators driven by dichotomous fluctuating frequency Lei Jiang(姜磊), Li Lai(赖莉), Tao Yu(蔚涛), Maokang Luo(罗懋康) Chin. Phys. B, 2021, 30 (6):  060502.  DOI: 10.1088/1674-1056/abd9b0 Abstract ( 479 )   HTML ( 2 )   PDF (1054KB) ( 129 )   The collective behaviors of two coupled harmonic oscillators with dichotomous fluctuating frequency are investigated, including stability, synchronization, and stochastic resonance (SR). First, the synchronization condition of the system is obtained. When this condition is satisfied, the mean-field behavior is consistent with any single particle behavior in the system. On this basis, the stability condition and the exact steady-state solution of the system are derived. Comparative analysis shows that, the stability condition is stronger than the synchronization condition, that is to say, when the stability condition is satisfied, the system is both synchronous and stable. Simulation analysis indicates that increasing the coupling strength will reduce the synchronization time. In weak coupling region, there is an optimal coupling strength that maximizes the output amplitude gain (OAG), thus the coupling-induced SR behavior occurs. In strong coupling region, the two particles are bounded as a whole, so that the coupling effect gradually disappears.

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Time-varying coupling-induced logical stochastic resonance in a periodically driven coupled bistable system Yuangen Yao(姚元根) Chin. Phys. B, 2021, 30 (6):  060503.  DOI: 10.1088/1674-1056/abd76c Abstract ( 532 )   HTML ( 1 )   PDF (1174KB) ( 216 )   Coupling-induced logical stochastic resonance (LSR) can be observed in a noise-driven coupled bistable system where the behaviors of system can be interpreted consistently as a specific logic gate in an appropriate noise level. Here constant coupling is extended to time-varying coupling, and then we investigate the effect of time-varying coupling on LSR in a periodically driven coupled bistable system. When coupling intensity oscillates periodically with the same frequency with periodic force or relatively high frequency, the system successfully yields the desired logic output. When coupling intensity oscillates irregularly with phase disturbance, large phase disturbance reduces the area of optimal parameter region of coupling intensity and response speed of logic devices. Although the system behaves as a desired logic gate when the frequency of time-periodic coupling intensity is precisely equal to that of periodic force, the desired logic gate is not robust against tiny frequency difference and phase disturbance. Therefore, periodic coupling intensity with high frequency ratio is an optimal option to obtain a reliable and robust logic operation.

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Dynamics of high-frequency modulated waves in a nonlinear dissipative continuous bi-inductance network S M Ngounou and F B Pelap Chin. Phys. B, 2021, 30 (6):  060504.  DOI: 10.1088/1674-1056/abd751 Abstract ( 370 )   HTML ( 1 )   PDF (3421KB) ( 105 )   This paper presents intensive investigation of dynamics of high frequency nonlinear modulated excitations in a damped bimodal lattice. The effects of the dissipation are considered through a linear dissipation coefficient whose evolution in terms of the carrier wave frequency is checked. There appears that the dissipation coefficient increases with the carrier wave frequency. In the linear limit and for high frequency waves, study of the asymptotic behavior of plane waves reveals the existence of two additional regions in the dispersion curve where the modulational phenomenon is observed compared to the lossless line. Based on the multiple scales method exploited in the continuum approximation using an appropriate decoupling ansatz for the voltage of the two different cells, it appears that the motion of modulated waves is described by a dissipative complex Ginzburg-Landau equation instead of a Korteweg-de Vries equation. We also show that this amplitude wave equation admits envelope and hole solitons in the high frequency mode. From basic sources, we design a programmable electronic generator of complex signals with desired characteristics, which delivers signals exploited as input waves for all our numerical simulations. These simulations are performed in the LTspice software that uses realistic components and give the results that corroborate perfectly our analytical predictions.

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Behaviors of thermalization for the Fermi-Pasta-Ulam-Tsingou system with small number of particles Zhenjun Zhang(张振俊), Jing Kang(康静), and Wen Wen(文文) Chin. Phys. B, 2021, 30 (6):  060505.  DOI: 10.1088/1674-1056/abd92f Abstract ( 431 )   HTML ( 1 )   PDF (659KB) ( 98 )   We study the behaviors of thermalization in Fermi-Pasta-Ulam-Tsingou (FPUT) system with small number of particles using periodic boundary conditions. The total energy has initially equidistributed among some of the lowest frequency modes. The thermalization time teq depending on system's energy density ε scales as teq ∝ ε-4 only within a certain range of nonlinearity. In this range of nonlinearity, energies can interchange between the initial excited modes and other modes continuously with time until reaching the thermalized state. With a further decreasing nonlinearity, a steeper growth than ε-4 will appear. In the very weakly nonlinear regime, energies on low frequency modes are found to be frozen on large time scales. Redistribution of mode energies happens through the resonances of high frequency modes.

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Complex network perspective on modelling chaotic systems via machine learning Tong-Feng Weng(翁同峰), Xin-Xin Cao(曹欣欣), and Hui-Jie Yang(杨会杰) Chin. Phys. B, 2021, 30 (6):  060506.  DOI: 10.1088/1674-1056/abd9b3 Abstract ( 562 )   HTML ( 6 )   PDF (2925KB) ( 182 )   Recent advances have demonstrated that a machine learning technique known as "reservoir computing" is a significantly effective method for modelling chaotic systems. Going beyond short-term prediction, we show that long-term behaviors of an observed chaotic system are also preserved in the trained reservoir system by virtue of network measurements. Specifically, we find that a broad range of network statistics induced from the trained reservoir system is nearly identical with that of a learned chaotic system of interest. Moreover, we show that network measurements of the trained reservoir system are sensitive to distinct dynamics and can in turn detect the dynamical transitions in complex systems. Our findings further support that rather than dynamical equations, reservoir computing approach in fact provides an alternative way for modelling chaotic systems.

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An image encryption algorithm based on improved baker transformation and chaotic S-box Xing-Yuan Wang(王兴元), Huai-Huai Sun(孙怀怀), and Hao Gao(高浩) Chin. Phys. B, 2021, 30 (6):  060507.  DOI: 10.1088/1674-1056/abdea3 Abstract ( 513 )   HTML ( 4 )   PDF (5157KB) ( 223 )   The algorithm is an image encryption algorithm based on the improved baker transformation and chaotic substitution box (S-box). It mainly uses the initial values and parameters of a one-dimensional logistic chaotic system as an encryption key. Specifically, in the image scrambling stage, the algorithm primarily uses an improved baker transform method to process the image. In the image diffusion stage, the algorithm first uses the chaotic S-box method to process the encryption key. Secondly, an exclusive OR (XOR) operation is performed on the image and the encryption key to initially diffuse the image. Finally, the image is again diffused using the method of ortho XOR. Simulation analysis shows that the algorithm can achieve good encryption effect, simple and easy implementation, and good security. In the digital image communication transmission, it has good practical value.

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Fractal sorting vector-based least significant bit chaotic permutation for image encryption Yong-Jin Xian(咸永锦), Xing-Yuan Wang(王兴元), Ying-Qian Zhang(张盈谦), Xiao-Yu Wang(王晓雨), and Xiao-Hui Du(杜晓慧) Chin. Phys. B, 2021, 30 (6):  060508.  DOI: 10.1088/1674-1056/abda35 Abstract ( 1923 )   HTML ( 32 )   PDF (10704KB) ( 2021 )   The image's least significant bit (LSB) covers lots of the details that have been commonly used in image encryption analysis. The newly proposed fractal sorting vector (FSV) and FSV-based LSB chaotic permutation (FSV-LSBCP) is a novel chaotic image encryption cryptosystem introduced in this article. The FSV-LSBCP effectively strengthens the security of the cryptographic scheme concerning the properties of the FSV. Key analysis, statistical analysis, resistance differential attack analysis, and resistance to cropping attacks and noise attacks are the focus of the suggested image encryption cryptosystem. The security experiment shows that the cryptosystem is adequate to achieve the desired degree of security.

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Generating multi-layer nested chaotic attractor and its FPGA implementation Xuenan Peng(彭雪楠), Yicheng Zeng(曾以成), Mengjiao Wang(王梦蛟), and Zhijun Li(李志军) Chin. Phys. B, 2021, 30 (6):  060509.  DOI: 10.1088/1674-1056/abda34 Abstract ( 472 )   HTML ( 3 )   PDF (2264KB) ( 90 )   Complex chaotic sequences are widely employed in real world, so obtaining more complex sequences have received highly interest. For enhancing the complexity of chaotic sequences, a common approach is increasing the scroll-number of attractors. In this paper, a novel method to control system for generating multi-layer nested chaotic attractors is proposed. At first, a piecewise (PW) function, namely quadratic staircase function, is designed. Unlike pulse signals, each level-logic of this function is square constant, and it is easy to realize. Then, by introducing the PW functions to a modified Chua's system with cubic nonlinear terms, the system can generate multi-layer nested Chua's attractors. The dynamical properties of the system are numerically investigated. Finally, the hardware implementation of the chaotic system is used FPGA chip. Experimental results show that theoretical analysis and numerical simulation are right. This chaotic oscillator consuming low power and utilization less resources is suitable for real applications.

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Signal-recycled weak measurement for ultrasensitive velocity estimation Sen-Zhi Fang(方森智), Yang Dai(戴阳), Qian-Wen Jiang(姜倩文), Hua-Tang Tan(谭华堂), Gao-Xiang Li(李高翔), and Qing-Lin Wu(吴青林) Chin. Phys. B, 2021, 30 (6):  060601.  DOI: 10.1088/1674-1056/abda2d Abstract ( 510 )   HTML ( 2 )   PDF (948KB) ( 95 )   Weak value amplification has shown its superiority in measurement of small physical effects. Here we introduce a signal-recycled weak-value-based velocity measurement strategy to decrease the attenuation of detected photons during the post-selection. Like the power-recycled scheme, we can improve the number of detected photons and signal-to-noise ratio of velocity by forming a cavity. However, optimal improvements of number of detected photons and signal-to-noise ratio cannot be obtained simultaneously in our signal-recycled scheme owing to the walk-off effect. Furthermore, we find that the reflected light is relatively strong compared with the power-recycled scheme, which may increase the collection-detection efficiency in prospective relevant experiment.

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Differentiable programming and density matrix based Hartree-Fock method Hong-Bin Ren(任宏斌), Lei Wang(王磊), and Xi Dai(戴希) Chin. Phys. B, 2021, 30 (6):  060701.  DOI: 10.1088/1674-1056/abeeed Abstract ( 491 )   HTML ( 3 )   PDF (591KB) ( 192 )   Differentiable programming is an emerging programming paradigm that allows people to take derivative of an output of arbitrary code snippet with respect to its input. It is the workhorse behind several well known deep learning frameworks, and has attracted significant attention in scientific machine learning community. In this paper, we introduce and implement a density matrix based Hartree-Fock method that naturally fits into the demands of this paradigm, and demonstrate it by performing fully variational ground state calculation on several representative chemical molecules.

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Magnetic shielding property for cylinder with circular, square, and equilateral triangle holes Si-Yuan Hao(郝思源), Xiao-Ping Lou(娄小平), Jing Zhu(祝静), Guang-Wei Chen(陈广伟), and Hui-Yu Li(李慧宇) Chin. Phys. B, 2021, 30 (6):  060702.  DOI: 10.1088/1674-1056/abeeee Abstract ( 598 )   HTML ( 2 )   PDF (1256KB) ( 289 )   The shielding property of cylinder with circular, square, and equilateral triangle holes was investigated by finite element analysis (FEA). The hole area (Shole) plays an important role in magnetic circuit on the surface of cylinder. When Shole is less than the critical area (SH), cylinder with three shapes of holes obtained the same remanent magnetization inside, indicating that the shielding property is unaffected by the shape of the hole. Hence, high-permeability material is the major path of the magnetic field. On the condition of Shole > SH, the sequence of the shielding property is equilateral triangle > square > circular, resulting from magnetoresistance of leakage flux in air dielectric. Besides, the anisotropy of shielding property caused by hole structural differences of the cylinder is evaluated. We find that a good shielding effectiveness is gained in the radial direction, compared with the axis direction. This research focuses on providing a theoretical support for the design of magnetic shield and improvement on the magnetic shielding ability.

ATOMIC AND MOLECULAR PHYSICS

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Charge disturbance/excitation in the Raman virtual state revealed by ROA signal: A case study of pinane Ziqi Zhu(祝子祺), Peijie Wang(王培杰), and Guozhen Wu(吴国祯) Chin. Phys. B, 2021, 30 (6):  063101.  DOI: 10.1088/1674-1056/abea90 Abstract ( 601 )   HTML ( 1 )   PDF (554KB) ( 154 )   The Raman mode intensities are used to extract the bond polarizabilities which are the indication of the charge disturbance/excitation of the Raman virtual state. A classical formula based on the electric and magnetic dipolar coupling among the charges on the atoms is developed which relates the charges and vibrational amplitudes of the atoms in a normal mode to the Raman optical activity (ROA) mode signatures. By fitting with the experimental ROA signatures, we are able to elucidate the scaling parameter which relates the bond polarizability to the electric charge. The result shows that around 40% of the charges in pinane are involved in the Raman process under 532 nm laser excitation.

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Production of dual species Bose-Einstein condensates of 39K and 87Rb Cheng-Dong Mi(米成栋), Khan Sadiq Nawaz, Peng-Jun Wang(王鹏军), Liang-Chao Chen(陈良超), Zeng-Ming Meng(孟增明), Lianghui Huang(黄良辉), and Jing Zhang(张靖) Chin. Phys. B, 2021, 30 (6):  063401.  DOI: 10.1088/1674-1056/abee6d Abstract ( 640 )   HTML ( 1 )   PDF (1348KB) ( 206 )   We report the production of 39K and 87Rb Bose-Einstein condensates (BECs) in the lowest hyperfine states|F=1,mF=1 angle simultaneously. We collect atoms in bright/dark magneto-optical traps (MOTs) of 39K/87Rb to overcome the light-assisted losses of 39K atoms. Gray molasses cooling on the D1 line of the 39K is used to effectively increase the phase density, which improves the loading efficiency of 39K into the quadrupole magnetic trap. Simultaneously, the normal molasses is employed for 87Rb. After the microwave evaporation cooling on 87Rb in the optically plugged magnetic trap, the atoms mixture is transferred to a crossed optical dipole trap, where the collisional properties of the two species in different combinations of the hyperfine states are studied. The dual species BECs of 39K and 87Rb are obtained by further evaporative cooling in an optical dipole trap at a magnetic field of 372.6 G with the background repulsive interspecies scattering length aKRb=34a0 (a0 is the Bohr radius) and the intraspecies scattering length aK=20.05a0.

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

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Characteristic mode analysis of wideband high-gain and low-profile metasurface antenna Kun Gao(高坤), Xiang-Yu Cao(曹祥玉), Jun Gao(高军), Huan-Huan Yang(杨欢欢), and Jiang-Feng Han(韩江枫) Chin. Phys. B, 2021, 30 (6):  064101.  DOI: 10.1088/1674-1056/abdb23 Abstract ( 629 )   HTML ( 2 )   PDF (1764KB) ( 311 )   A wideband high-gain and low-profile metasurface antenna is proposed by analyzing characteristic quantities and parameters in the characteristic modes (CMs). The detailed modal current and modal weighting coefficient are analyzed to explain the broadband operation and high gain. A dominant characteristic mode is well excited, leading to a broadband operation. The mode behaviors of the excitation are changed to suppress the unwanted higher-order modes and improve the radiation performance by changing the widths of two patches. The measured impedance bandwidth for -10 dB is 39.8% (5.3 GHz-7.94 GHz) with a gain of 7.8 dBi-10.04 dBi over the operating bandwidth.

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Real time high accuracy phase contrast imaging with parallel acquisition speckle tracking Zhe Hu(胡哲), Wen-Qiang Hua(滑文强), and Jie Wang(王 劼) Chin. Phys. B, 2021, 30 (6):  064201.  DOI: 10.1088/1674-1056/abee08 Abstract ( 454 )   HTML ( 2 )   PDF (1428KB) ( 64 )   X-ray speckle tracking based methods can provide results with best reported angular accuracy up to 2 nrad. However, duo to the multi-frame requirement for phase retrieval and the possible instability of the x-ray beam, mechanical and background vibration, the actual accuracy will inevitably be degraded by these time-dependent fluctuations. Therefore, not only spatial position, but also temporal features of the speckle patterns need to be considered in order to maintain the superiority of the speckle-based methods. In this paper, we propose a parallel acquisition method with advantages of real time and high accuracy, which has potential applicability to dynamic samples imaging as well as on-line beam monitoring. Through simulations, we demonstrate that the proposed method can reduce the phase error caused by the fluctuations to 1% at most compared with current speckle tracking methods. Meanwhile, it can keep the accuracy deterioration within 0.03 nrad, making the high theoretical accuracy a reality. Also, we find that waveforms of the incident beam have a little impact on the phase retrieved and will not influence the actual accuracy, which relaxes the requirements for speckle-based experiments.

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High speed ghost imaging based on a heuristic algorithm and deep learning Yi-Yi Huang(黄祎祎), Chen Ou-Yang(欧阳琛), Ke Fang(方可), Yu-Feng Dong(董玉峰), Jie Zhang(张杰), Li-Ming Chen(陈黎明), and Ling-An Wu(吴令安) Chin. Phys. B, 2021, 30 (6):  064202.  DOI: 10.1088/1674-1056/abea8c Abstract ( 587 )   HTML ( 5 )   PDF (1451KB) ( 298 )   We report an overlapping sampling scheme to accelerate computational ghost imaging for imaging moving targets, based on reordering a set of Hadamard modulation matrices by means of a heuristic algorithm. The new condensed overlapped matrices are then designed to shorten and optimize encoding of the overlapped patterns, which are shown to be much superior to the random matrices. In addition, we apply deep learning to image the target, and use the signal acquired by the bucket detector and corresponding real image to train the neural network. Detailed comparisons show that our new method can improve the imaging speed by as much as an order of magnitude, and improve the image quality as well.

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Perfect photon absorption based on the optical parametric process Yang Zhang(张旸), Yu-Bo Ma(马宇波), Xin-Ping Li(李新平), Yu Guo(郭钰), and Chang-Shui Yu(于长水) Chin. Phys. B, 2021, 30 (6):  064203.  DOI: 10.1088/1674-1056/abd7d9 Abstract ( 456 )   HTML ( 1 )   PDF (565KB) ( 72 )   The perfect photon absorption is studied in a cavity quantum electrodynamics (CQED) system, in which an optical parameter amplifier (OPA) is coupled to the cavity mode. This makes it possible to control the optical phase to realize the perfect photon absorption. It is found that in the presence of one and two injected fields, the perfect photon absorption is present in these two cases and can be controlled by adjusting the parametric phase. Moreover, different from the previous predictions of perfect photon absorption in atomic CQED systems, the perfect photon absorption can be changed significantly by the relative phase. Our work provides a new platform to use the parametric processes to make an available way to control the behaviors of photons and to take advantage of the optical phase to achieve the perfect photon absorption.

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Effective Hamiltonian of the Jaynes-Cummings model beyond rotating-wave approximation Yi-Fan Wang(王伊凡), Hong-Hao Yin(尹洪浩), Ming-Yue Yang(杨明月), An-Chun Ji(纪安春), and Qing Sun(孙青) Chin. Phys. B, 2021, 30 (6):  064204.  DOI: 10.1088/1674-1056/abd930 Abstract ( 648 )   HTML ( 1 )   PDF (748KB) ( 545 )   The Jaynes-Cummings model with or without rotating-wave approximation plays a major role to study the interaction between atom and light. We investigate the Jaynes-Cummings model beyond the rotating-wave approximation. Treating the counter-rotating terms as periodic drivings, we solve the model in the extended Floquet space. It is found that the full energy spectrum folded in the quasi-energy bands can be described by an effective Hamiltonian derived in the high-frequency regime. In contrast to the Z2 symmetry of the original model, the effective Hamiltonian bears an enlarged U(1) symmetry with a unique photon-dependent atom-light detuning and coupling strength. We further analyze the energy spectrum, eigenstate fidelity and mean photon number of the resultant polaritons, which are shown to be in accordance with the numerical simulations in the extended Floquet space up to an ultra-strong coupling regime and are not altered significantly for a finite atom-light detuning. Our results suggest that the effective model provides a good starting point to investigate the rich physics brought by counter-rotating terms in the frame of Floquet theory.

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Graphene-tuned threshold gain to achieve optical pulling force on microparticle Hong-Li Chen(陈鸿莉) and Yang Huang(黄杨) Chin. Phys. B, 2021, 30 (6):  064205.  DOI: 10.1088/1674-1056/abd9b4 Abstract ( 400 )   HTML ( 1 )   PDF (692KB) ( 67 )   We investigate optical force on a graphene-coated gain microparticle by adopting the Maxwell's stress tensor method. It is found that there exists a threshold gain in obtaining the Fano-profile optical force which indicates the reversal of optical pushing and pulling force. And giant pushing/pulling force can be achieved if the gain value of the material is in the proximity of the threshold gain. Our results show that the threshold gain is more sensitive to the relaxation time than to the Fermi energy of the graphene. We further study the optical force on larger microparticle to demonstrate the pulling force occurring at octupole resonance with small gain value and then it will appear at quadrupole resonance by increasing gain value. Our work provides an in-depth insight into the interaction between light and gain material and gives the additional degree of freedom to optical manipulation of microparticle.

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Multiple scattering and modeling of laser in fog Ji-Yu Xue(薛积禹), Yun-Hua Cao(曹运华), Zhen-Sen Wu(吴振森), Jie Chen(陈杰), Yan-Hui Li(李艳辉), Geng Zhang(张耿), Kai Yang(杨凯), and Ruo-Ting Gao(高若婷) Chin. Phys. B, 2021, 30 (6):  064206.  DOI: 10.1088/1674-1056/abddab Abstract ( 562 )   HTML ( 2 )   PDF (991KB) ( 250 )   When a laser is transmitted in fog, and the water droplets will scatter and absorb the laser, which affects the intensity of the laser transmission and the accuracy of radar detection. Therefore, it is of great significance to study the laser transmission in the fog. At present, the main method of calculating the scattering and attenuation characteristics of fog is based on the radiation transmission theory, which is realized by a large number of numerical calculations or physical simulation methods, which takes time and cannot meet the requirements for obtaining the fast and accurate results. Therefore, in this paper established are a new laser forward attenuation model and backward attenuation model in low visibility fog. It is found that in low visibility environments, the results calculated by the Monte Carlo method are more accurate than those from most of the existing forward attenuation models. For the cases of 0.86-μm, 1.06-μm, 1.315-μm, 10.6-μm typical lasers incident on different fogs with different visibilities, a backscatter model is established, the error between the fitting result and the calculation result is analyzed, the backward attenuation fitting parameters of the new model are tested, and a more accurate fitting result is obtained.

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Aperture-averaged scintillation index and fade statistics in weak oceanic turbulence Hao Wang(王昊), Fu-Zeng Kang(康福增), Xuan Wang(王瑄), Wei Zhao(赵卫), and Shu-Wei Sun(孙枢为) Chin. Phys. B, 2021, 30 (6):  064207.  DOI: 10.1088/1674-1056/abd756 Abstract ( 530 )   HTML ( 2 )   PDF (668KB) ( 162 )   With the rapid demand for underwater optical communication (UOC), studies of UOC degradation by oceanic turbulence have attached increasing attention worldwide and become a research hot-spot in recent years. Previous studies used a simplified and inaccurate oceanic turbulence spectrum, in which the eddy diffusivity ratio between temperature and salinity is assumed to be unity and the outer scale of turbulence is assumed to be infinite. However, both assumptions are not true in most of the actual marine environments. In this paper, based on the Rytov theory in weak turbulence, we derive analytical expressions of "the aperture-averaged scintillation index" (SI) for both plane and spherical waves, which can clearly demonstrate how SI is influenced by several key factors in UOC. Then, typical fade statistics of the UOC system in weak turbulence is discussed including the probability of fade, the expected number of fades per time, the mean fade time, signal-to-noise ratio and bit error rate. Our results show that spherical wave is preferable in the UOC system in weak turbulence compared to plane wave, and the aperture-averaged effect has a significant impact on UOC system's performance. Our results can be used to determine those key parameters for designing the UOC system over reasonable ranges.

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Comprehensive studies on dielectric properties of p-methoxy benzylidene p-decyl aniline with function of temperature and frequency in planar geometry: A potential nematic liquid crystal for display devices Pankaj Kumar Tripathi, Kunwar Vikram, Mithlesh Tiwari, and Ajay Shriram Chin. Phys. B, 2021, 30 (6):  064208.  DOI: 10.1088/1674-1056/abdda9 Abstract ( 479 )   HTML ( 2 )   PDF (2163KB) ( 86 )   The dielectric properties of the nematic mesophase, p-methoxy benzylidene p-decyl aniline (MBDA), measured in planar geometry with a function of frequency and temperature are investigated in detail. The complex dielectric permittivity (ε' and ε″) is also studied at a bias voltage of 10 V for planar aligned sample cell of nematic mesophase. The dielectric permittivity with bias voltage attains a higher (> 2 times) value than that without bias voltage at a temperature of 56℃, which is due to the fact that the linking group of nematic molecules is internally interacted with an applied bias voltage. This is supported by observing an enhanced dielectric permittivity of nematic liquid crystal (LC) in the presence of bias voltage, which can be fully explained as the increasing of the corresponding dipole moment. The dielectric relaxation behaviors of nematic LC are also demonstrated for planar aligned sample cell. The remarkable results are observed that the relaxation frequency shifts into low frequency region with the increase of the bias voltage applied to the planar aligned sample cells. The dielectric relaxation spectra are fitted by Cole-Cole nonlinear curve fitting for nematic mesophase in order to determine the dielectric strength.

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Dynamic modulation in graphene-integrated silicon photonic crystal nanocavity Long-Pan Wang(汪陇盼), Cheng Ren(任承), De-Zhong Cao(曹德忠), Rui-Jun Lan(兰瑞君), and Feng Kang(康凤) Chin. Phys. B, 2021, 30 (6):  064209.  DOI: 10.1088/1674-1056/abda2b Abstract ( 596 )   HTML ( 2 )   PDF (798KB) ( 111 )   Silicon-based electro-optic modulators are the key devices in integrated optoelectronics. Integration of the graphene layer and the photonic crystal (PC) cavity is a promising way of achieving compact modulators with high efficiency. In this paper, a high-quality (Q) acceptor-type PC nanocavity is employed to integrate with a single-layer graphene for realizing strong modulation. Through tuning the chemical potential of graphene, a large wavelength shift of 2.62 nm and a Q factor modulation of larger than 5 are achieved. A modulation depth (12.8 dB) of the reflection spectrum is also obtained. Moreover, the optimized PC nanocavity has a large free spectral range of 131.59 nm, which can effectively enhance the flexibility of the modulator. It shows that the proposed graphene-based PC nanocavity is a potential candidate for compact, high-contrast, and low-power absorptive modulators in integrated silicon chips.

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A 90° mixed-mode twisted nematic liquid-crystal-on-silicon with an insulating protrusion structure Wen-Juan Li(李文娟), Yu-Qiang Guo(郭玉强), Chi Zhang(张弛), Hong-Mei Ma(马红梅), and Yu-Bao Sun(孙玉宝) Chin. Phys. B, 2021, 30 (6):  064210.  DOI: 10.1088/1674-1056/abee0b Abstract ( 478 )   HTML ( 1 )   PDF (2439KB) ( 169 )   A 90° mixed-mode twisted nematic liquid-crystal-on-silicon (90°-MTN LCoS) with protrusion located between the adjacent pixels is proposed to reduce the effect of fringing field. The influence of the protrusion with different widths from 0.5 μm to 0.9 μm and different heights from 0.3 μm to 0.7 μm is investigated. The results demonstrate that the invalid pixel region width can be reduced by 31.5% via using the protrusion with the suitable width and height compared with no protrusion case, which provides a higher display quality, such as the higher reflectance and contrast ratio.

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Degenerate cascade fluorescence: Optical spectral-line narrowing via a single microwave cavity Liang Hu(胡亮), Xiang-Ming Hu(胡响明), and Qing-Ping Hu(胡庆平) Chin. Phys. B, 2021, 30 (6):  064211.  DOI: 10.1088/1674-1056/abd76b Abstract ( 526 )   HTML ( 1 )   PDF (1193KB) ( 194 )   For a three-level atom, two nondegenerate (even microwave and optical) electric dipole transitions are usually allowed; for either of these, the fluorescence spectra are well-described in terms of spontaneous transitions from a triplet of dressed sublevels to an adjacent lower-lying triplet. When the three dressed sublevels are equally spaced from each other, a remarkable feature known as degenerate cascade fluorescence takes place, which displays a five-peaked structure. We show that a single cavity can make all the spectral lines extremely narrow, whether they arise from cavity-coupled or cavity-free transitions. This effect is based on intrinsic cascade lasing feedback and makes it possible to use a single microwave cavity (even a bad cavity) to narrow the spectral lines in the optical frequency regime.

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Generation of multi-wavelength square pulses in the dissipative soliton resonance regime by a Yb-doped fiber laser Xude Wang(汪徐德), Simin Yang(杨思敏), Mengqiu Sun(孙梦秋), Xu Geng(耿旭), Jieyu Pan (潘婕妤), Shuguang Miao(苗曙光), and Suwen Li(李素文) Chin. Phys. B, 2021, 30 (6):  064212.  DOI: 10.1088/1674-1056/abd6f4 Abstract ( 605 )   HTML ( 1 )   PDF (828KB) ( 93 )   Multi-wavelength square pulses are generated in the dissipative soliton resonance (DSR) regime by a Yb-doped fiber laser (YDFL) with a long cavity configuration. The spectral filter effect provided by a passive fiber with low-stress birefringence facilitates the establishment of multi-wavelength operation. Through appropriate control of the cavity parameters, a multi-wavelength DSR pulse can be generated in single- and dual-waveband regions. When the multi-wavelength DSR works in the 1038 nm waveband, the pulse duration can broaden from 2 ns to 37.7 ns. The maximum intra-cavity pulse energy is 152.7 nJ. When the DSR works in the 1038 nm and 1080 nm wavebands, the pulse duration can be tuned from 2.3 ns to 10.5 ns with rising pump power. The emergence of the 1080 nm waveband is attributed to the stimulated Raman scattering (SRS) effect. Our work might help a deeper insight to be gained into DSR pulses in all-normal-dispersion YDFLs.

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An approach to gas sensors based on tunable diode laser incomplete saturated absorption spectra Wei Nie(聂伟), Zhen-Yu Xu(许振宇), Rui-Feng Kan(阚瑞峰), Mei-Rong Dong(董美蓉), and Ji-Dong Lu(陆继东) Chin. Phys. B, 2021, 30 (6):  064213.  DOI: 10.1088/1674-1056/abd769 Abstract ( 604 )   HTML ( 1 )   PDF (2770KB) ( 101 )   A spectral profile reconstruction method that can be applied to incomplete saturated-absorption spectra is proposed and demonstrated. Through simulation and theoretical calculation, it is proved that compared with the traditional whole-profile fitting method, this new method can increase the concentration detection upper limit of a single absorption line by about 8.7 times. High-concentration water vapor is measured using TDLAS technology, the total water vapor pressure and the self-broadened half-width coefficient of the spectrum were simultaneously measured from incomplete saturated-absorption spectra and compared with high-precision pressure sensors and the HITRAN databases. Their maximum relative deviations were about 4.63% and 9.10%, respectively. These results show that the spectral profile reconstruction method has great application potential for expanding the dynamic range of single-line measurements to higher concentrations, especially for in-situ online measurements under complex conditions, such as over large temperature and concentration dynamic ranges.

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Efficient realization of daytime radiative cooling with hollow zigzag SiO2 metamaterials Huawei Yao(姚华伟), Xiaoxia Wang(王晓霞), Huaiyuan Yin(殷怀远), Yuanlin Jia(贾渊琳), Yong Gao(高勇), Junqiao Wang(王俊俏), and Chunzhen Fan(范春珍) Chin. Phys. B, 2021, 30 (6):  064214.  DOI: 10.1088/1674-1056/abd697 Abstract ( 483 )   HTML ( 1 )   PDF (1075KB) ( 115 )   A tunable selective emitter with hollow zigzag SiO2 metamaterials, which are deposited on Si3N4 and Ag film, is proposed and numerically investigated for achieving excellent radiative cooling effects. The average emissivity reaches a high value of 98.7% in the atmospheric window and possesses a high reflectivity of 92.0% in the solar spectrum. To reveal the enhanced absorptivity, the confined electric field distribution is investigated, and it can be well explained by moth eye effects. Moreover, tunable emissivity can also be initiated with different incident angles and it stays above 83% when the incident angle is less than 80°, embodying the excellent cooling performance in the atmospheric transparency window. Its net cooling power achieves 100.6 W·m-2, with a temperature drop of 13°, and the cooling behavior can persist in the presence of non-radiative heat exchange conditions. Therefore, high and tunable selective emitters based on our designed structure could provide a new route to realizing high-performance radiative cooling. This work is also of great significance for saving energy and environmental protection.

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Surface plasmon polaritons induced reduced hacking Bakhtawar, Muhammad Haneef, and Humayun Khan Chin. Phys. B, 2021, 30 (6):  064215.  DOI: 10.1088/1674-1056/abd7e5 Abstract ( 395 )   HTML ( 1 )   PDF (528KB) ( 86 )   There is always need for secure transmission of information and simultaneously compact-size photonic circuits. This can be achieved if surface plasmon-polaritons (SPPs) are used as source of information, and the reduced hacking as the transmission phenomenon. In this article, an SPP-based reduced hacking scheme is presented at interface between atomic medium and metallic conductor. The SPP propagation is manipulated with conductivity of the metal. The delay or advance of the SPP is found to create nanosecond time gap which can be used for storing and sending the information safely. The reduced hacking is further modified with conductivity of the metal and the control parameters of the atomic medium.

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Parameter accuracy analysis of weak-value amplification process in the presence of noise Jiangdong Qiu(邱疆冬), Zhaoxue Li(李兆雪), Linguo Xie(谢林果), Lan Luo(罗兰), Yu He(何宇), Changliang Ren(任昌亮), Zhiyou Zhang(张志友), and Jinglei Du(杜惊雷) Chin. Phys. B, 2021, 30 (6):  064216.  DOI: 10.1088/1674-1056/abcfa0 Abstract ( 471 )   HTML ( 1 )   PDF (491KB) ( 103 )   We theoretically introduce the statistical uncertainty of photon number and phase error to discuss the precision of parameters to be measured based on weak measurements. When the photon counting scheme is used, we discuss the relative accuracy of the system in the presence of phase error by using the orthogonal and nonorthogonal pre- and post-selected states, respectively. When using the measurement scheme of pointer shift, we discuss the measurement accuracy in the presence of phase error, pointer resolution, and statistical uncertainty. These results give a guide way to get the smallest relative precision and deepen our understanding about weak measurement.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

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Numerical simulation and experimental validation of multiphysics field coupling mechanisms for a high power ICP wind tunnel Ming-Hao Yu(喻明浩), Zhe Wang(王哲), Ze-Yang Qiu(邱泽洋), Bo Lv(吕博), and Bo-Rui Zheng(郑博睿) Chin. Phys. B, 2021, 30 (6):  065201.  DOI: 10.1088/1674-1056/abeb0e Abstract ( 578 )   HTML ( 1 )   PDF (4229KB) ( 181 )   We take the established inductively coupled plasma (ICP) wind tunnel as a research object to investigate the thermal protection system of re-entry vehicles. A 1.2-MW high power ICP wind tunnel is studied through numerical simulation and experimental validation. The distribution characteristics and interaction mechanism of the flow field and electromagnetic field of the ICP wind tunnel are investigated using the multi-field coupling method of flow, electromagnetic, chemical, and thermodynamic field. The accuracy of the numerical simulation is validated by comparing the experimental results with the simulation results. Thereafter, the wind tunnel pressure, air velocity, electron density, Joule heating rate, Lorentz force, and electric field intensity obtained using the simulation are analyzed and discussed. The results indicate that for the 1.2-MW ICP wind tunnel, the maximum values of temperature, pressure, electron number density, and other parameters are observed during coil heating. The influence of the radial Lorentz force on the momentum transfer is stronger than that of the axial Lorentz force. The electron number density at the central axis and the amplitude and position of the Joule heating rate are affected by the radial Lorentz force. Moreover, the plasma in the wind tunnel is constantly in the subsonic flow state, and a strong eddy flow is easily generated at the inlet of the wind tunnel.

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Time-resolved radial uniformity of pulse-modulated inductively coupled O2/Ar plasmas Wei Liu(刘巍), Chan Xue(薛婵), Fei Gao(高飞), Yong-Xin Liu(刘永新), You-Nian Wang(王友年), and Yong-Tao Zhao(赵永涛) Chin. Phys. B, 2021, 30 (6):  065202.  DOI: 10.1088/1674-1056/abe3f5 Abstract ( 507 )   HTML ( 1 )   PDF (945KB) ( 121 )   Time-resolved radial uniformity of pulse-modulated inductively coupled O2/Ar plasma has been investigated by means of a Langmuir probe as well as an optical probe in this paper. The radial uniformity of plasma has been discussed through analyzing the nonuniformity factor β (calculated by the measured ne, lower β means higher plasma radial uniformity). The results show that during the active-glow period, the radial distribution of ne exhibits an almost flat profile at the beginning phase, but it converts into a parabola-like profile during the steady state. The consequent evolution for β is that when the power is turned on, it declines to a minimum at first, and then it increases to a maximum, after that, it decays until it keeps constant. This phenomenon can be explained by the fact that the ionization gradually becomes stronger at the plasma center and meanwhile the rebuilt electric field (plasma potential and ambipolar potential) will confine the electrons at the plasma center as well. Besides, the mean electron energy (<ε>on) at the pulse beginning decreases with the increasing duty cycle. This will postpone the plasma ignition after the power is turned on. This phenomenon has been verified by the emission intensity of Ar (λ=750.4 nm). During the after-glow period, it is interesting to find that the electrons have a large depletion rate at the plasma center. Consequently, ne forms a hollow distribution in the radial direction at the late stage of after-glow. Therefore, β exhibits a maximum at the same time. This can be attributed to the formation of negative oxygen ion (O-) at the plasma center when the power has been turned off.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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Effects of short-range attraction on Jamming transition Zhenhuan Xu(徐震寰), Rui Wang(王瑞), Jiamei Cui(崔佳梅), Yanjun Liu(刘彦君), and Wen Zheng(郑文) Chin. Phys. B, 2021, 30 (6):  066101.  DOI: 10.1088/1674-1056/abefc5 Abstract ( 489 )   HTML ( 1 )   PDF (713KB) ( 147 )   Enormous progresses to understand the jamming transition have been driven via simulating purely repulsive particles which were somehow idealized in the past two decades. While the attractive systems are both theoretical and practical compared with repulsive systems. By studying the statistics of rigid clusters, we find that the critical packing fraction φc varies linearly with attraction μ for different system sizes when the range of attraction is short. While for systems with long-range attractions, however, the slope of φc appears significantly different, which means that there are two distinct jamming scenarios. In this paper, we focus our main attention on short-range attractions scenario and define a new quantity named "short-range attraction susceptibility" χp, which describes the degree of response of the probability of finding jammed states pj to short-range attraction strength μ. Our central results are that χp diverges in the thermodynamic limit as χp ∝|φ-φc∞|-γp, where φc∞ is the packing fraction at the jamming transition for the infinite system in the absence of attraction. χp obeys scaling collapse with a scaling function in both two and three dimensions, illuminating that the jamming transition can be considered as a phase transition as proposed in previous work.

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Novel rubidium polyfluorides with F3, F4, and F5 species Ziyue Lin(林子越), Hongyu Yu(于洪雨), Hao Song(宋昊), Zihan Zhang(张子涵), Tianxiao Liang(梁天笑), Mingyang Du(杜明阳), and Defang Duan(段德芳) Chin. Phys. B, 2021, 30 (6):  066102.  DOI: 10.1088/1674-1056/abefc6 Abstract ( 555 )   HTML ( 3 )   PDF (898KB) ( 253 )   Pressure has an important effect on chemical bonds and their chemical properties. The atypical compounds NaCl3 and CsF3 are predicted to be stable at high pressure and show unique physical and chemical properties. By using ab initio random structure searching and density functional theory calculations, we predicted multiple thermodynamically stable atypical compounds, which are RbF2, RbF3, RbF4, and RbF5 in the pressure range of 0-300 GPa. In these stable compounds, homonuclear bondings of F3, F4, and F5 species are easily formed. The electron structure calculation showed that except for Fd-3m phase of RbF2, these stable compounds are insulators and F 5p orbitals play an important role in the Fermi level. It is interesting that the compounds RbF5 could be stable at nearly ambient pressure and 0 K which will stimulate experimental studies in the future.

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Reconstruction and interpretation of photon Doppler velocimetry spectrum for ejecta particles from shock-loaded sample in vacuum Xiao-Feng Shi(石晓峰), Dong-Jun Ma(马东军), Song-lin Dang(党松琳), Zong-Qiang Ma(马宗强), Hai-Quan Sun(孙海权), An-Min He(何安民), and Pei Wang(王裴) Chin. Phys. B, 2021, 30 (6):  066201.  DOI: 10.1088/1674-1056/abd9b2 Abstract ( 498 )   HTML ( 2 )   PDF (899KB) ( 113 )   The photon Doppler velocimetry (PDV) spectrum is investigated in an attempt to reveal the particle parameters of ejecta from shock-loaded samples in a vacuum. A GPU-accelerated Monte-Carlo algorithm, which considers the multiple-scattering effects of light, is applied to reconstruct the light field of the ejecta and simulate the corresponding PDV spectrum. The influence of the velocity profile, total area mass, and particle size of the ejecta on the simulated spectra is discussed qualitatively. To facilitate a quantitative discussion, a novel theoretical optical model is proposed in which the single-scattering assumption is applied. With this model, the relationships between the particle parameters of ejecta and the peak information of the PDV spectrum are derived, enabling direct extraction of the particle parameters from the PDV spectrum. The values of the ejecta parameters estimated from the experimental spectrum are in good agreement with those measured by a piezoelectric probe.

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Hydrogen-induced dynamic slowdown of metallic glass-forming liquids Jin-Ai Gao(高津爱), Hai-Shen Huang(黄海深), and Yong-Jun Lü(吕勇军) Chin. Phys. B, 2021, 30 (6):  066301.  DOI: 10.1088/1674-1056/abf111 Abstract ( 549 )   HTML ( 0 )   PDF (801KB) ( 123 )   Dynamics of hydrogen doped Cu50Zr50 glass-forming liquids are investigated by using the newly developed modified embedded atomic method (MEAM) potential based on molecular dynamics simulations. We find that the doping of hydrogen atoms slows down the relaxation dynamics, reduces the fragility of supercooled melts, and promotes the occurrence of glass transitions. The dynamic slowdown is suggested to be closely related to the effect of hydrogen atoms on locally ordered structure of melts. With increasing concentration of hydrogen, the five-fold symmetry associated with Cu- and Zr-centered polyhedrons is lowered, on the other hand, the local order featuring metal hydrides is enhanced. The latter dominates the dynamic behaviors of glass-forming liquids, especially for Zr atoms, and results in the dynamic slowdown.

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Crystallization evolution and relaxation behavior of high entropy bulk metallic glasses using microalloying process Danhong Li(李丹虹), Changyong Jiang(江昌勇), Hui Li(栗慧), and Mahander Pandey Chin. Phys. B, 2021, 30 (6):  066401.  DOI: 10.1088/1674-1056/abd92c Abstract ( 481 )   HTML ( 1 )   PDF (815KB) ( 89 )   The role of the microalloying process in relaxation behavior and crystallization evolution of Zr20Cu20Ni20Ti20Hf20 high entropy bulk metallic glass (HEBMG) was investigated. We selected Al and Nb elements as minor elements, which led to the negative and positive effects on the heat of mixing in the master HEBMG composition, respectively. According to the results, both elements intensified β relaxation in the structure; however, α relaxation remained stable. By using different frequencies in dynamic mechanical analysis, it was revealed that the activation energy of β relaxation for the Nb-added sample was much higher, which was due to the creation of significant structural heterogeneity under the microalloying process. Moreover, it was found that Nb addition led to a diversity in crystallization stages at the supercooled liquid region. It was suggested that the severe structural heterogeneity in the Nb-added sample provided multiple energy-level sites in the structure for enhancing the crystallization stages.

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Effects of W6+ occupying Sc3+ on the structure, vibration, and thermal expansion properties of scandium tungstate Dongxia Chen(陈冬霞), Qiang Sun(孙强), Zhanjun Yu(于占军), Mingyu Li(李明玉), Juan Guo(郭娟), Mingju Chao(晁明举), and Erjun Liang(梁二军) Chin. Phys. B, 2021, 30 (6):  066501.  DOI: 10.1088/1674-1056/abd7d4 Abstract ( 590 )   HTML ( 2 )   PDF (1141KB) ( 98 )   We experimentally investigate effects of W6+ occupying the sites of Sc3+ in the unit cell of Sc2W3O12 (Sc8W12O48) on the structure, vibration and thermal expansion. The composition and structure of the doped sample (Sc6W2)W12O48±δ (with two W6+ occupying two sites of Sc3+ in the unit cell of Sc8W12O48) are analyzed and identified by combining the x-ray photoelectron spectroscopy and the synchronous x-ray diffraction with first-principles calculations based on density functional theory. Results show that the crystal with even W6+ occupying even Sc3+ in the unit cell is stable and maintains the orthorhombic structure at room temperature. The structure of the doped sample is similar to that of Sc2W3O12, and with even W occupying even positions of Sc in the unit cell and constituting the WO6 octahedra. Raman analyses show that the doped sample possesses stronger W-O bonds and wider Raman linewidths than those of Sc2W3O12. The sample doped with W also exhibits intrinsic negative thermal expansion in the measured range of 150 K-650 K.

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Floquet bands and photon-induced topological edge states of graphene nanoribbons Weijie Wang(王威杰), Xiaolong Lü(吕小龙), and Hang Xie(谢航) Chin. Phys. B, 2021, 30 (6):  066701.  DOI: 10.1088/1674-1056/abddaa Abstract ( 646 )   HTML ( 2 )   PDF (4811KB) ( 177 )   Floquet theorem is widely used in the light-driven systems. But many 2D-materials models under the radiation are investigated with the high-frequency approximation, which may not be suitable for the practical experiment. In this work, we employ the non-perturbative Floquet method to strictly investigate the photo-induced topological phase transitions and edge states properties of graphene nanoribbons under the light irradiation of different frequencies (including both low and high frequencies). By analyzing the Floquet energy bands of ribbon and bulk graphene, we find the cause of the phase transitions and its relation with edge states. Besides, we also find the size effect of the graphene nanoribbon on the band gap and edge states in the presence of the light.

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Bose-Einstein condensates under a non-Hermitian spin-orbit coupling Hao-Wei Li(李浩伟) and Jia-Zheng Sun(孙佳政) Chin. Phys. B, 2021, 30 (6):  066702.  DOI: 10.1088/1674-1056/abd7e4 Abstract ( 492 )   HTML ( 1 )   PDF (839KB) ( 235 )   We study the properties of Bose-Einstein condensates under a non-Hermitian spin-orbit coupling (SOC), induced by a dissipative two-photon Raman process. We focus on the dynamics of the condensate at short times, when the impact of decoherence induced by quantum jumps is negligible and the dynamics is coherently driven by a non-Hermitian Hamiltonian. Given the significantly modified single-particle physics by dissipative SOC, the interplay of non-Hermiticity and interaction leads to a quasi-steady-state phase diagram different from its Hermitian counterpart. In particular, we find that dissipation can induce a phase transition from the stripe phase to the plane-wave phase. We further map out the phase diagram with respect to the dissipation and interaction strengths, and finally investigate the stability of quasi-steady states through the time-dependent dissipative Gross-Pitaevskii equation. Our results are readily accessible based on standard experiments with synthetic spin-orbit couplings.

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Superfluid phases and excitations in a cold gas of d-wave interacting bosonic atoms and molecules Zehan Li(李泽汉), Jian-Song Pan, and W Vincent Liu Chin. Phys. B, 2021, 30 (6):  066703.  DOI: 10.1088/1674-1056/abd7d7 Abstract ( 579 )   HTML ( 1 )   PDF (1156KB) ( 110 )   Motivated by recent advances in orbitally tuned Feshbach resonance experiments, we analyze the ground-state phase diagram and related low-energy excitation spectra of a d-wave interacting Bose gas. A two-channel model with d-wave symmetric interactions and background s-wave interactions is adopted to characterize the gas. The ground state is found to have three interesting superfluid phases:atomic, molecular, and atomic-molecular. In great contrast to what was previously known about the p-wave case, the atomic superfluid is found to be momentum-independent for the d-wave case discussed here. The Bogoliubov spectra above each superfluid phase are obtained both analytically and numerically.

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In-plane oriented CH3NH3PbI3 nanowire suppression of the interface electron transfer to PCBM Tao Wang(王涛), Zhao-Hui Yu(于朝辉), Hao Huang(黄昊), Wei-Guang Kong(孔伟光), Wei Dang(党伟), and Xiao-Hui Zhao(赵晓辉) Chin. Phys. B, 2021, 30 (6):  066801.  DOI: 10.1088/1674-1056/abf4fa Abstract ( 471 )   HTML ( 1 )   PDF (1473KB) ( 81 )   One-dimensional nanowire is an important candidate for lead-halide perovskite-based photonic detectors and solar cells. Its surface population, diameter, and growth direction, etc., are critical for device performance. In this research, we carried out a detailed study on electron transfer process at the interface of nanowire CH3NH3PbI3(N-MAPbI3)/Phenyl C61 butyric acid methyl-ester synonym (PCBM), as well as the interface of compact CH3NH3PbI3(C-MAPbI3)/PCBM by transient absorption spectroscopy. By comparing the carrier recombination dynamics of N-MAPbI3, N-MAPbI3/PCBM, C-MAPbI3, and C-MAPbI3/PCBM from picosecond (ps) to hundred nanosecond (ns) time scale, it is demonstrated that electron transfer at N-MAPbI3/PCBM interface is less efficient than that at C-MAPbI3/PCBM interface. In addition, electron transfer efficiency at C-MAPbI3/PCBM interface was found to be excitation density-dependent, and it reduces with photo-generation carrier concentration increasing in a range from 1.0×1018 cm-3-4.0×1018 cm-3. Hot electron transfer, which leads to acceleration of electron transfer between the interfaces, was also visualized as carrier concentration increases from 1.0×1018 cm-3-2.2×1018 cm-3.

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

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Anisotropic thermoelectric transport properties in polycrystalline SnSe2 Caiyun Li(李彩云), Wenke He(何文科), Dongyang Wang(王东洋), and Li-Dong Zhao(赵立东) Chin. Phys. B, 2021, 30 (6):  067101.  DOI: 10.1088/1674-1056/abeee1 Abstract ( 591 )   HTML ( 0 )   PDF (1192KB) ( 220 )   It is reported that SnSe2 consisting of the same elements as SnSe, is a new promising thermoelectric material with advantageous layered structure. In this work, the thermoelectric performance of polycrystalline SnSe2 is improved through introducing SnSe phase and electron doping (Cl doped in Se sites). The anisotropic transport properties of SnSe2 are investigated. A great reduction of the thermal conductivity is achieved in SnSe2 through introducing SnSe phase, which mainly results from the strong SnSe2-SnSe inter-phase scattering. Then the carrier concentration is optimized via Cl doping, leading to a great enhancement of the electrical transport properties, thus an extraordinary power factor of ~5.12 μW·cm-1·K-2 is achieved along the direction parallel to the spark plasma sintering (SPS) pressure direction (||P). Through the comprehensive consideration on the anisotropic thermoelectric transport properties, an enhanced figure of merit ZT is attained and reaches to ~0.6 at 773 K in SnSe2-2% SnSe after 5% Cl doping along the||P direction, which is much higher than ~0.13 and ~0.09 obtained in SnSe2-2% SnSe and pristine SnSe2 samples, respectively.

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Tuning transport coefficients of monolayer MoSi2N4 with biaxial strain Xiao-Shu Guo(郭小姝) and San-Dong Guo(郭三栋) Chin. Phys. B, 2021, 30 (6):  067102.  DOI: 10.1088/1674-1056/abdb22 Abstract ( 496 )   HTML ( 1 )   PDF (2264KB) ( 208 )   Experimentally synthesized MoSi2N4 (Science 369 670 (2020)) is a piezoelectric semiconductor. Here, we systematically study the large biaxial (isotropic) strain effects (0.90-1.10) on electronic structures and transport coefficients of monolayer MoSi2N4 by density functional theory (DFT). With a/a0 from 0.90 to 1.10, the energy band gap firstly increases, and then decreases, which is due to transformation of conduction band minimum (CBM). Calculated results show that the MoSi2N4 monolayer is mechanically stable in the considered strain range. It is found that the spin-orbital coupling (SOC) effects on Seebeck coefficient depend on the strain. In unstrained MoSi2N4, the SOC has neglected influence on Seebeck coefficient. However, the SOC can produce important influence on Seebeck coefficient, when the strain is applied, for example, 0.96 strain. The compressive strain can change relative position and numbers of conduction band extrema (CBE), and then the strength of conduction bands convergence can be enhanced, to the benefit of n-type ZTe. Only about 0.96 strain can effectively improve n-type ZTe. Our works imply that strain can effectively tune the electronic structures and transport coefficients of monolayer MoSi2N4, and can motivate farther experimental exploration.

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Magnetic impurity in hybrid and type-II nodal line semimetals Xiao-Rong Yang(杨晓容), Zhen-Zhen Huang(黄真真), Wan-Sheng Wang(王万胜), and Jin-Hua Sun(孙金华) Chin. Phys. B, 2021, 30 (6):  067103.  DOI: 10.1088/1674-1056/abfa02 Abstract ( 418 )   HTML ( 3 )   PDF (5849KB) ( 59 )   We study the Kondo screening of a spin-1/2 magnetic impurity in the hybrid nodal line semimetals (NLSMs) and the type-II NLSMs by using the variational method. We mainly study the binding energy and the spin-spin correlation between magnetic impurity and conduction electrons. We find that in both the hybrid and type-II cases, the density of states (DOS) is always finite, so the impurity and the conduction electrons always form bound states, and the bound state is more easily formed when the DOS is large. Meanwhile, due to the unique dispersion relation and the spin-orbit couplings in the NLSMs, the spatial spin-spin correlation components show very interesting features. Most saliently, various components of the spatial spin-spin correlation function decay with 1/r2 in the hybrid NLSMs, while they follow 1/r3 decay in the type-II NLSMs. This property is mainly caused by the special band structures in the NLSMs, and it can work as a fingerprint to distinguish the two types of NLSMs.

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Cobalt anchored CN sheet boosts the performance of electrochemical CO oxidation Xu Liu(刘旭), Jun-Chao Huang(黄俊超), and Xiang-Mei Duan(段香梅) Chin. Phys. B, 2021, 30 (6):  067104.  DOI: 10.1088/1674-1056/abfbd7 Abstract ( 422 )   HTML ( 1 )   PDF (3877KB) ( 76 )   Single-atom catalysts (SACs) have attracted great interest due to their significant roles played in applications of environmental protection, energy conversion, energy storage, and so on. Using first-principles calculations with dispersion-correction, we investigated the structural stability and catalytic activity of Co implanted CN sheet towards CO oxidation. The adsorption energy of CO and O2 on the catalysts Co@CN and 2Co@CN are close, thus preventing CO poisoning. Among three possible CO oxidation mechanisms, termolecular Eley-Rideal is the most appropriate reaction path, and the corresponding rate-limiting reaction barriers of the two systems are 0.42 eV and 0.38 eV, respectively.

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High sensitive chiral molecule detector based on the amplified lateral shift in Kretschmann configuration involving chiral TDBCs Song Wang(王松), Qihui Ye(叶起惠), Xudong Chen(陈绪栋), Yanzhu Hu(胡燕祝), and Gang Song(宋钢) Chin. Phys. B, 2021, 30 (6):  067301.  DOI: 10.1088/1674-1056/abdda6 Abstract ( 520 )   HTML ( 2 )   PDF (549KB) ( 84 )   We investigate a high sensitive chiral molecule detector based on Goos-Hanchen shift (S) in Kretschmann configuration involving chiral tri (diethylene glycol monobutyl) citrates (TDBCs). Fresnel equations and the stationary phase method are employed to calculate S. Due to the interaction between surface plasmon polaritons and chiral TDBCs, S with chiral TDBCs are amplified at near the resonant wavelengths of chiral TDBCs. Our calculation results show that although the difference between the resonant wavelengths of left and right TDBCs is 4.5 nm, the positions of the largest S for the structures with left TDBCs and right TDBCs do not overlap. S reaches 400 times (or 200 times) the incident wavelength around the resonant wavelength of left TDBCs (or right TDBCs). The difference of S with chiral TDBCs (ΔS) can reach 400 times or 200 times the incident wavelength in certain conditions, which can be directly observed in experiments. Left TDBCs and right TDBCs are easily distinguished. There is an optimal thickness of the metal film to realize the largest difference of S between Kretschmann configurations with left TDBCs and right TDBCs. Furthermore, we discuss the oscillator strength f, which is mainly determined by TDBC concentration. We find that our proposed detector is quite sensitive with f. By changing f from 0.008 to 0.014 with the step of 0.002, the change of ΔS is no less than five times the incident wavelength (2.9 μ). Our proposed structure is very sensitive to the chirality and the concentration of TDBCs and has potential applications in distinguishing the chirality detector.

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Device topological thermal management of β-Ga2O3 Schottky barrier diodes Yang-Tong Yu(俞扬同), Xue-Qiang Xiang(向学强), Xuan-Ze Zhou(周选择), Kai Zhou(周凯), Guang-Wei Xu(徐光伟), Xiao-Long Zhao(赵晓龙), and Shi-Bing Long(龙世兵) Chin. Phys. B, 2021, 30 (6):  067302.  DOI: 10.1088/1674-1056/abeee2 Abstract ( 582 )   HTML ( 3 )   PDF (1138KB) ( 267 )   The ultra-wide bandgap semiconductor β gallium oxide (β-Ga2O3) gives promise to low conduction loss and high power for electronic devices. However, due to the natural poor thermal conductivity of β-Ga2O3, their power devices suffer from serious self-heating effect. To overcome this problem, we emphasize on the effect of device structure on peak temperature in β-Ga2O3 Schottky barrier diodes (SBDs) using TCAD simulation and experiment. The SBD topologies including crystal orientation of β-Ga2O3, work function of Schottky metal, anode area, and thickness, were simulated in TCAD, showing that the thickness of β-Ga2O3 plays a key role in reducing the peak temperature of diodes. Hence, we fabricated β-Ga2O3 SBDs with three different thickness epitaxial layers and five different thickness substrates. The surface temperature of the diodes was measured using an infrared thermal imaging camera. The experimental results are consistent with the simulation results. Thus, our results provide a new thermal management strategy for high power β-Ga2O3 diode.

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Terminal-optimized 700-V LDMOS with improved breakdown voltage and ESD robustness Jie Xu(许杰), Nai-Long He(何乃龙), Hai-Lian Liang(梁海莲), Sen Zhang(张森), Yu-De Jiang(姜玉德), and Xiao-Feng Gu(顾晓峰) Chin. Phys. B, 2021, 30 (6):  067303.  DOI: 10.1088/1674-1056/abdda7 Abstract ( 601 )   HTML ( 9 )   PDF (1025KB) ( 147 )   A novel terminal-optimized triple RESURF LDMOS (TOTR-LDMOS) is proposed and verified in a 0.25-μ bipolar-CMOS-DMOS (BCD) process. By introducing a low concentration region to the terminal region, the surface electric field of the TOTR-LDMOS decreases, helping to improve the breakdown voltage (BV) and electrostatic discharge (ESD) robustness. Both traditional LDMOS and TOTR-LDMOS are fabricated and investigated by transmission line pulse (TLP) tests, direct current (DC) tests, and TCAD simulations. The results show that comparing with the traditional LDMOS, the BV of the TOTR-LDMOS increases from 755 V to 817 V without affecting the specific on-resistance (Ron,sp) of 6.99 Ω·mm2. Meanwhile, the ESD robustness of the TOTR-LDMOS increases by 147%. The TOTR-LDMOS exhibits an excellent performance among the present 700-V LDMOS devices.

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Floquet topological phase transition in two-dimensional quadratic band crossing system Guo-Bao Zhu(朱国宝) and Hui-Min Yang(杨慧敏) Chin. Phys. B, 2021, 30 (6):  067304.  DOI: 10.1088/1674-1056/abdda4 Abstract ( 393 )   HTML ( 1 )   PDF (680KB) ( 127 )   We investigate the Hall effects of quadratic band crossing (QBC) fermions in a square optical lattice with spin-orbit coupling and orbital Zeeman term. We find that the orbital Zeeman term and shaking play critical roles in the systems, which can drive a topological transition from spin Hall phases to anomalous Hall phase with nonvanishing (spin) Chern numbers. Due to the interplay among the orbital Zeeman term, spin-orbit coupling, and the shaking, the phase diagram of the system exhibits rich phases, which are characterized by Chern number.

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Design and simulation of AlN-based vertical Schottky barrier diodes Chun-Xu Su(苏春旭), Wei Wen(温暐), Wu-Xiong Fei(费武雄), Wei Mao(毛维), Jia-Jie Chen(陈佳杰), Wei-Hang Zhang(张苇杭), Sheng-Lei Zhao(赵胜雷), Jin-Cheng Zhang(张进成), and Yue Hao(郝跃) Chin. Phys. B, 2021, 30 (6):  067305.  DOI: 10.1088/1674-1056/abe0c7 Abstract ( 615 )   HTML ( 5 )   PDF (879KB) ( 128 )   The key parameters of vertical AlN Schottky barrier diodes (SBDs) with variable drift layer thickness (DLT) and drift layer concentration (DLC) are investigated. The specific on-resistance (Ron,sp) decreased to 0.5 mΩ·cm2 and the breakdown voltage (VBR) decreased from 3.4 kV to 1.1 kV by changing the DLC from 1015 cm-3 to 3×1016 cm-3. The VBR increases from 1.5 kV to 3.4 kV and the Ron,sp also increases to 12.64 mΩ·cm2 by increasing DLT from 4-μ to 11-μ. The VBR enhancement results from the increase of depletion region extension. The Baliga's figure of merit (BFOM) of 3.8 GW/cm2 was obtained in the structure of 11-μ DLT and 1016 cm-3 DLC without FP. When DLT or DLC is variable, the consideration of the value of BFOM is essential. In this paper, we also present the vertical AlN SBD with a field plate (FP), which decreases the crowding of electric field in electrode edge. All the key parameters were optimized by simulating based on Silvaco-ATLAS.

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Electrochemical liftoff of freestanding GaN by a thick highly conductive sacrificial layer grown by HVPE Xiao Wang(王骁), Yu-Min Zhang(张育民), Yu Xu(徐俞), Zhi-Wei Si(司志伟), Ke Xu(徐科), Jian-Feng Wang(王建峰), and Bing Cao(曹冰) Chin. Phys. B, 2021, 30 (6):  067306.  DOI: 10.1088/1674-1056/abd6fa Abstract ( 501 )   HTML ( 1 )   PDF (1852KB) ( 103 )   Separation technology is an indispensable step in the preparation of freestanding GaN substrate. In this paper, a large-area freestanding GaN layer was separated from the substrate by an electrochemical liftoff process on a sandwich structure composed of an Fe-doped GaN substrate, a highly conductive Si-doped sacrificial layer and a top Fe-doped layer grown by hydride vapor phase epitaxy (HVPE). The large difference between the resistivity in the Si-doped layer and Fe-doped layer resulted in a sharp interface between the etched and unetched layer. It was found that the etching rate increased linearly with the applied voltage, while it continuously decreased with the electrochemical etching process as a result of the mass transport limitation. Flaky GaN pieces and nitrogen gas generated from the sacrificial layer by electrochemical etching were recognized as the main factors responsible for the blocking of the etching channel. Hence, a thick Si-doped layer grown by HVPE was used as the sacrificial layer to alleviate this problem. Moreover, high temperature and ultrasonic oscillation were also found to increase the etching rate. Based on the results above, we succeeded in the liftoff of ~1.5 inch GaN layer. This work could help reduce the cost of freestanding GaN substrate and identifies a new way for mass production.

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Effects of post-annealing on crystalline and transport properties of Bi2Te3 thin films Qi-Xun Guo(郭奇勋), Zhong-Xu Ren(任中旭), Yi-Ya Huang(黄意雅), Zhi-Chao Zheng(郑志超), Xue-Min Wang(王学敏), Wei He(何为), Zhen-Dong Zhu(朱振东), and Jiao Teng(滕蛟) Chin. Phys. B, 2021, 30 (6):  067307.  DOI: 10.1088/1674-1056/abee6c Abstract ( 639 )   HTML ( 1 )   PDF (1874KB) ( 219 )   A well-established method is highly desirable for growing topological insulator thin films with low carrier density on a wafer-level scale. Here, we present a simple, scalable method based on magnetron sputtering to obtain high-quality Bi2Te3 films with the carrier density down to 4.0×1013 cm-2. In contrast to the most-used method of high substrate temperature growth, we firstly sputtered Bi2Te3 thin films at room temperature and then applied post-annealing. It enables the growth of highly-oriented Bi2Te3 thin films with larger grain size and smoother interface. The results of electrical transport show that it has a lower carrier density as well as a larger coherent length (~228 nm, 2 K). Our studies pave the way toward large-scale, cost-effective production of Bi2Te3 thin films to be integrated with other materials in wafer-level scale for electronic and spintronic applications.

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Temperature and doping dependent flat-band superconductivity on the Lieb-lattice Feng Xu(徐峰), Lei Zhang(张磊), and Li-Yun Jiang(姜立运) Chin. Phys. B, 2021, 30 (6):  067401.  DOI: 10.1088/1674-1056/abdea5 Abstract ( 567 )   HTML ( 1 )   PDF (1422KB) ( 80 )   We consider the superconducting properties of Lieb lattice, which produces a flat-band energy spectrum in the normal state under the strong electron-electron correlation. Firstly, we show the hole-doping dependent superconducting order amplitude with various electron-electron interaction strengths in the zero-temperature limit. Secondly, we obtain the superfluid weight and Berezinskii-Kosterlitz-Thouless (BKT) transition temperature with a lightly doping level. The large ratio between the gap-opening temperature and BKT transition temperature shows similar behavior to the pseudogap state in high-Tc superconductors. The BKT transition temperature versus doping level exhibits a dome-like shape in resemblance to the superconducting dome observed in the high-Tc superconductors. However, unlike the exponential dependence of Tc on the electron-electron interaction strength in the conventional high-Tc superconductors, the BKT transition temperature for a flat band system depends linearly on the electron-electron interaction strength. We also show the doping-dependent superconductivity on a lattice with the staggered hoping parameter in the end. Our predictions are amenable to verification in the ultracold atoms experiment and promote the understanding of the anomalous behavior of the superfluid weight in the high-Tc superconductors.

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Pressure-induced anomalous insulating behavior in frustrated iridate La3Ir3O11 Chun-Hua Chen(陈春华), Yong-Hui Zhou(周永惠), Ying Zhou(周颖), Yi-Fang Yuan(袁亦方), Chao An(安超), Xu-Liang Chen(陈绪亮), Zhao-Ming Tian(田召明), and Zhao-Rong Yang(杨昭荣) Chin. Phys. B, 2021, 30 (6):  067402.  DOI: 10.1088/1674-1056/abf100 Abstract ( 630 )   HTML ( 1 )   PDF (1106KB) ( 193 )   The geometrically frustrated iridate La3Ir3O11 with strong spin-orbit coupling and fractional valence was recently predicted to be a quantum spin liquid candidate at ambient conditions. Here, we systematically investigate the evolution of structural and electronic properties of La3Ir3O11 under high pressure. Electrical transport measurements reveal an abnormal insulating behavior rather than metallization above a critical pressure Pc ~38.7 GPa. Synchrotron x-ray diffraction (XRD) experiments indicate the stability of the pristine cubic KSbO3-type structure up to 73.1 GPa. Nevertheless, when the pressure gradually increases across Pc, the bulk modulus gets enhanced and the pressure dependence of bond length dIr-Ir undergoes a slope change. Consistent with the XRD data, detailed analyses of Raman spectra reveal an abnormal redshift of Raman mode and a change of Raman intensity around Pc. Our results demonstrate that the pressure-induced insulating behavior in La3Ir3O11 can be assigned to the structural modification, such as the distortion of IrO6 octahedra. These findings will shed light on the emergent abnormal insulating behavior in other 5d iridates reported recently.

RAPID COMMUNICATION

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Unusual electronic structure of Dirac material BaMnSb2 revealed by angle-resolved photoemission spectroscopy Hot! Hongtao Rong(戎洪涛), Liqin Zhou(周丽琴), Junbao He(何俊宝), Chunyao Song(宋春尧), Yu Xu(徐煜), Yongqing Cai(蔡永青), Cong Li(李聪), Qingyan Wang(王庆艳), Lin Zhao(赵林), Guodong Liu(刘国东), Zuyan Xu(许祖彦), Genfu Chen(陈根富), Hongming Weng(翁红明), and Xingjiang Zhou(周兴江) Chin. Phys. B, 2021, 30 (6):  067403.  DOI: 10.1088/1674-1056/ac0036 Abstract ( 964 )   HTML ( 1 )   PDF (2780KB) ( 460 )   High resolution angle resolved photoemission measurements and band structure calculations are carried out to study the electronic structure of BaMnSb2. All the observed bands are nearly linear that extend to a wide energy range. The measured Fermi surface mainly consists of one hole pocket around Γ and a strong spot at Y which are formed from the crossing points of the linear bands. The measured electronic structure of BaMnSb2 is unusual and deviates strongly from the band structure calculations. These results will stimulate further efforts to theoretically understand the electronic structure of BaMnSb2 and search for novel properties in this Dirac material.

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

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Bias-controlled spin memory and spin injector scheme in the tunneling junction with a single-molecule magnet Zheng-Zhong Zhang(张正中) and Hao Liu(刘昊) Chin. Phys. B, 2021, 30 (6):  067501.  DOI: 10.1088/1674-1056/abd9b1 Abstract ( 547 )   HTML ( 1 )   PDF (1531KB) ( 171 )   A bias-controlled spin-filter and spin memory is theoretically proposed, which consists of the junction with a single-molecule magnet sandwiched between the nonmagnetic and ferromagnetic (FM) leads. By applying different voltage pulses Vwrite across the junction, the spin direction of the single-molecule magnet can be controlled to be parallel or anti-parallel to the magnetization of the FM lead, and the spin direction of SMM can be "read out" either by the magneto-resistance or by the spin current with another series of small voltage pulses Vprobe. It is shown that the polarization of the spin current is extremely high (up to 100%) and can be manipulated by the full-electric manner. This device scheme can be compatible with current technologies and has potential applications in high-density memory devices.

RAPID COMMUNICATION

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Powder x-ray diffraction and Rietveld analysis of (C2H5NH3)2CuCl4 Yi Liu(刘义), Jun Shen(沈俊), Zunming Lu(卢遵铭), Baogen Shen(沈保根), and Liqin Yan(闫丽琴) Chin. Phys. B, 2021, 30 (6):  067502.  DOI: 10.1088/1674-1056/abee0a Abstract ( 751 )   HTML ( 1 )   PDF (1515KB) ( 252 )   Structural properties of the organic-inorganic hybrid (C2H5NH3)2CuCl4 (EA2CuCl4) have been investigated by means of x-ray powder diffraction and Rietveld analysis. A structural phase transition from Pbca to Aba2 occurs at T4=240 K, which results in a paraelectric-ferroelectric phase transition. The release of the Jahn-Teller distortion with increasing temperature toward T4 is revealed by the structural analysis.

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

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Effects of post-sinter annealing on microstructure and magnetic properties of Nd-Fe-B sintered magnets with Nd-Ga intergranular addition Jin-Hao Zhu(朱金豪), Lei Jin(金磊), Zhe-Huan Jin(金哲欢), Guang-Fei Ding(丁广飞), Bo Zheng(郑波), Shuai Guo(郭帅), Ren-Jie Chen(陈仁杰), and A-Ru Yan(闫阿儒) Chin. Phys. B, 2021, 30 (6):  067503.  DOI: 10.1088/1674-1056/abddad Abstract ( 621 )   HTML ( 1 )   PDF (3280KB) ( 137 )   We investigate the effects of post-sinter annealing on the microstructure and magnetic properties in B-lean Nd-Fe-B sintered magnets with different quantities of Nd-Ga intergranular additions. The magnet with fewer Nd-Ga additions can enhance 0.2 T in coercivity, with its remanences nearly unchanged after annealing. With the further increase of the Nd-Ga addition, the annealing process leads coercivity to increase 0.4 T, accompanied by a slight decrease of remanence. With the Nd-Ga addition further increasing and after annealing, however, the increase of coercivity is basically constant and the change of remanence is reduced. Microstructure observation indicates that the matrix grains are covered by continuous thin grain boundary phase in the magnets with an appropriate Nd-Ga concentration after the annealing process. However, the exceeding Nd-Ga addition brings out notable segregation of grain boundary phase, and prior formation of part RE6Fe13Ga phase in the sintered magnet. This prior formation results in a weaker change of remanence after the annealing process. Therefore, the diverse changes of magnetic properties with different Nd-Ga concentrations are based on the respective evolution of grain boundary after the annealing process.

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Magnetostriction and spin reorientation in ferromagnetic Laves phase Pr(GaxFe1-x)1.9 compounds Min-Yu Zeng(曾敏玉), Qing Tang(唐庆), Zhi-Wei Mei(梅志巍), Cai-Yan Lu(陆彩燕), Yan-Mei Tang(唐妍梅), Xiang Li(李翔), Yun He(何云), and Ze-Ping Guo(郭泽平) Chin. Phys. B, 2021, 30 (6):  067504.  DOI: 10.1088/1674-1056/abe1a3 Abstract ( 492 )   HTML ( 1 )   PDF (1179KB) ( 59 )   The magnetostriction, magnetization, and spin reorientation properties in Pr(GaxFe1-x)1.9 alloys have been investigated by high-precision x-ray diffraction (XRD) step scanning, magnetization, and Mössbauer spectra measurements. Ga substitution reduces the magnetostriction (λ||) with magnetic field H ≥ 8 kOe (1 Oe=1.33322×102 Pa), but it also increases the λ|| value when H ≤ 8 kOe at 5 K. Spin-reorientations (SR) are observed in all the alloys investigated, as determined by the step scanned XRD, Mössbauer spectra, and the abnormal temperature dependence of magnetization. An increase of the spin reorientation temperature (TSR) due to Ga substitution is found in the phase diagram, which is different from the decrease one in many R(TxFe1-x)1.9 (T=Co, Al, Mn) alloys. The present work provides a method to control the easy magnetization direction (EMD) or TSR for developing an anisotropic compensation system.

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Emergent O(4) symmetry at the phase transition from plaquette-singlet to antiferromagnetic order in quasi-two-dimensional quantum magnets Hot! Guangyu Sun(孙光宇), Nvsen Ma(马女森), Bowen Zhao(赵博文), Anders W. Sandvik, and Zi Yang Meng(孟子杨) Chin. Phys. B, 2021, 30 (6):  067505.  DOI: 10.1088/1674-1056/abf3b8 Abstract ( 864 )   HTML ( 1 )   PDF (4649KB) ( 434 )   Recent experiments[Guo et al., Phys. Rev. Lett. 124 206602 (2020)] on thermodynamic properties of the frustrated layered quantum magnet SrCu2(BO3)2—the Shastry-Sutherland material—have provided strong evidence for a low-temperature phase transition between plaquette-singlet and antiferromagnetic order as a function of pressure. Further motivated by the recently discovered unusual first-order quantum phase transition with an apparent emergent O(4) symmetry of the antiferromagnetic and plaquette-singlet order parameters in a two-dimensional "checkerboard J-Q" quantum spin model[Zhao et al., Nat. Phys. 15 678 (2019)], we here study the same model in the presence of weak inter-layer couplings. Our focus is on the evolution of the emergent symmetry as the system crosses over from two to three dimensions and the phase transition extends from strictly zero temperature in two dimensions up to finite temperature as expected in SrCu2(BO3)2. Using quantum Monte Carlo simulations, we map out the phase boundaries of the plaquette-singlet and antiferromagnetic phases, with particular focus on the triple point where these two ordered phases meet the paramagnetic phase for given strength of the inter-layer coupling. All transitions are first-order in the neighborhood of the triple point. We show that the emergent O(4) symmetry of the coexistence state breaks down clearly when the interlayer coupling becomes sufficiently large, but for a weak coupling, of the magnitude expected experimentally, the enlarged symmetry can still be observed at the triple point up to significant length scales. Thus, it is likely that the plaquette-singlet to antiferromagnetic transition in SrCu2(BO3)2 exhibits remnants of emergent O(4) symmetry, which should be observable due to additional weakly gapped Goldstone modes.

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Band alignment between NiOx and nonpolar/semipolar GaN planes for selective-area-doped termination structure Ji-Yao Du(都继瑶), Ji-Yu Zhou(周继禹), Xiao-Bo Li(李小波), Tao-Fei Pu(蒲涛飞), Liu-An Li(李柳暗), Xin-Zhi Liu(刘新智), and Jin-Ping Ao(敖金平) Chin. Phys. B, 2021, 30 (6):  067701.  DOI: 10.1088/1674-1056/abdb21 Abstract ( 428 )   HTML ( 2 )   PDF (847KB) ( 107 )   Band alignment between NiOx and nonpolar GaN plane and between NiOx and semipolar GaN plane are measured by x-ray photoelectron spectroscopy. They demonstrate that the maximum value of the valence band in the unintentional-doped a-plane, m-plane, and r-plane GaN are comparable to each other, which means that all the substrates are of n-type with similar background carrier concentrations. However, the band offset at the NiOx/GaN interface presents obvious crystalline plane dependency although they are coated with the same NiOx films. By fitting the Ga 3d spectrum obtained from the NiOx/GaN interface, we find that relatively high Ga-O content at the interface corresponds to a small band offset. On the one hand, the high Ga-O content on the GaN surface will change the growth mode of NiOx. On the other hand, the affinity difference between Ga and O forms a dipole which will introduce an extra energy band bending.

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Laser-induced thermal lens study of the role of morphology and hydroxyl group in the evolution of thermal diffusivity of copper oxide Riya Sebastian, M S Swapna, Vimal Raj, and S Sankararaman Chin. Phys. B, 2021, 30 (6):  067801.  DOI: 10.1088/1674-1056/abd9b5 Abstract ( 394 )   HTML ( 1 )   PDF (2327KB) ( 72 )   The paper explores the evolution of thermal behavior of the material by studying the variations in thermal diffusivity using the single beam thermal lens (TL) technique. For this purpose, the decomposition of Cu(OH)2 into CuO is studied in a time range up to 120 h, by subjecting the sample to morphological, structural, and spectroscopic characterizations. The time evolution of thermal diffusivity can be divided into three regions for demonstrating the dynamics of the reaction. When the reaction is complete, the thermal diffusivity is also found to be saturated. In addition to the morphological modifications, from rods to flakes, the variations in the amount of hydroxyl group are attributed to be responsible for the enhancement of base fluid's thermal diffusivity by 165%. Thus the study unveils the role of hydroxyl groups in the thermal behavior of CuO.

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Low-dimensional phases engineering for improving the emission efficiency and stability of quasi-2D perovskite films Yue Wang(王月), Zhuang-Zhuang Ma(马壮壮), Ying Li(李营), Fei Zhang(张飞), Xu Chen(陈旭), and Zhi-Feng Shi (史志锋) Chin. Phys. B, 2021, 30 (6):  067802.  DOI: 10.1088/1674-1056/abe92b Abstract ( 441 )   HTML ( 1 )   PDF (2805KB) ( 180 )   The two-dimensional (2D) Ruddlesden-Popper-type perovskites, possessing tunable bandgap, narrow light emission, strong quantum confinement effect, as well as a simple preparation method, are identified as a new generation of candidate materials for efficient light-emitting diodes. However, the preparation of high-quality quasi-2D perovskite films is still a challenge currently, such as the severe mixing of phases and a high density of defects within the films, impeding the further promotion of device performance. Here, we prepared the quasi-2D PEA2MAn-1PbnBr3n+1 perovskite films by a modified spin-coating method, and the phases with large bandgap were effectively suppressed by the vacuum evaporation treatment. We systematically investigated the optical properties and stability of the optimized films, and the photoluminescence (PL) quantum yield of the treated films was enhanced from 23% to 45%. We also studied the emission mechanisms by temperature-dependent PL spectra. Moreover, the stability of films against moisture, ultraviolet light, and heat was also greatly improved.

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Effects of substitution of group-V atoms for carbon or silicon atoms on optical properties of silicon carbide nanotubes Ying-Ying Yang(杨莹莹), Pei Gong(龚裴), Wan-Duo Ma(马婉铎), Rui Hao(郝锐), and Xiao-Yong Fang(房晓勇) Chin. Phys. B, 2021, 30 (6):  067803.  DOI: 10.1088/1674-1056/abdb1e Abstract ( 621 )   HTML ( 1 )   PDF (1287KB) ( 218 )   Silicon carbide nanotubes (SiCNTs) have broad application prospects in the field of micro-nanodevices due to their excellent physical properties. Based on first-principles, the difference between optical properties of SiCNTs where C atom or Si atom is replaced by group-V element is studied. The results show that the optical absorptions of SiCNTs doped by different elements are significantly different in the band of 600 nm-1500 nm. The differences in photoconductivity, caused by different doping elements, are reflected mainly in the band above 620 nm, the difference in dielectric function and refractive index of SiCNTs are reflected mainly in the band above 500 nm. Further analysis shows that SiCNTs doped with different elements change their band structures, resulting in the differences among their optical properties. The calculation of formation energy shows that SiCNTs are more stable when group-V element replaces Si atom, except N atom. These research results will be beneficial to the applications of SiC nanomaterials in optoelectronic devices and provide a theoretical basis for selecting the SiCNTs' dopants.

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Enhanced microwave absorption performance of MOF-derived hollow Zn-Co/C anchored on reduced graphene oxide Yue Wang(王玥), Dawei He(何大伟), and Yongsheng Wang(王永生) Chin. Phys. B, 2021, 30 (6):  067804.  DOI: 10.1088/1674-1056/abd770 Abstract ( 564 )   HTML ( 2 )   PDF (2773KB) ( 77 )   Composite materials assembled by metal/carbon nanoparticles and 2D layered flakes can provide abundant interfaces, which are beneficial for high-performance microwave absorbers. Herein, Zn-Co/C/RGO composites, composed of Zn-Co metal-organic framework-derived Zn-Co/C nanoparticles and reduced graphene oxide (RGO), were obtained through a facile method. The multilayer structure was due to the introduction of hollow Zn-Co/C nanoparticles in the RGO sheets. Zn-Co/C nanoparticles provided abundant polarization and dipole centers on the RGO surface, which enhanced the microwave absorption abilities. Different concentrations of RGO were introduced to optimize impedance matching. The minimum reflection loss (RL) of Zn-Co/C/RGO with a thickness of 1.5 mm reached -32.56 dB with the bandwidth corresponding to RL at -10 dB, which can reach 3.92 GHz, while a minimum RL of -47.15 dB at 11.2 GHz was also obtained at a thickness of 2.0 mm. The electromagnetic data demonstrate that Zn-Co/C/RGO presented excellent absorption performance and has potential for application in the microwave absorption field.

INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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Effect of metal nanoparticle doping concentration on surface morphology and field emission properties of nano-diamond films Yao Wang(王垚), Sheng-Wang Yu(于盛旺), Yan-Peng Xue(薛彦鹏), Hong-Jun Hei(黑鸿君), Yan-Xia Wu(吴艳霞), and Yan-Yan Shen(申艳艳) Chin. Phys. B, 2021, 30 (6):  068101.  DOI: 10.1088/1674-1056/abda33 Abstract ( 643 )   HTML ( 0 )   PDF (1611KB) ( 95 )   Nano-diamond particles are co-deposited on Ti substrates with metal (Ti/Ni) nanoparticles (NPs) by the electrophoretic deposition (EPD) method combined with a furnace annealing at 800℃ under N2 atmosphere. Modifications of structural and electron field emission (EFE) properties of the metal-doped films are investigated with different metal NPs concentrations. Our results show that the surface characteristics and EFE performances of the samples are first enhanced and then reduced with metal NPs concentration increasing. Both the Ti-doped and Ni-doped nano-diamond composite films exhibit optimal EFE and microstructural performances when the doping quantity is 5 mg. Remarkably enhanced EFE properties with a low turn-on field of 1.38 V/μm and a high current density of 1.32 mA/cm2 at an applied field of 2.94 V/μm are achieved for Ni-doped nano-diamond films, and are superior to those for Ti-doped ones. The enhancement of the EFE properties for the Ti-doped films results from the formation of the TiC-network after annealing. However, the doping of electron-rich Ni NPs and formation of high conductive graphitic phase are considered to be the factor, which results in marvelous EFE properties for these Ni-doped nano-diamond films.

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Synthesis and characterizations of boron and nitrogen co-doped high pressure and high temperature large single-crystal diamonds with increased mobility Xin-Yuan Miao(苗辛原), Hong-An Ma(马红安), Zhuang-Fei Zhang(张壮飞), Liang-Chao Chen(陈良超), Li-Juan Zhou(周丽娟), Min-Si Li(李敏斯), and Xiao-Peng Jia(贾晓鹏) Chin. Phys. B, 2021, 30 (6):  068102.  DOI: 10.1088/1674-1056/abf12c Abstract ( 699 )   HTML ( 4 )   PDF (2113KB) ( 252 )   We synthesized and investigated the boron-doped and boron/nitrogen co-doped large single-crystal diamonds grown under high pressure and high temperature (HPHT) conditions (5.9 GPa and 1290℃). The optical and electrical properties and surface characterization of the synthetic diamonds were observed and studied. Incorporation of nitrogen significantly changed the growth trace on surface of boron-containing diamonds. X-ray photoelectron spectroscopy (XPS) measurements showed good evident that nitrogen atoms successfully incorporate into the boron-rich diamond lattice and bond with carbon atoms. Raman spectra showed differences on the as-grown surfaces and interior between boron-doped and boron/nitrogen co-doped diamonds. Fourier transform infrared spectroscopy (FTIR) measurements indicated that the nitrogen incorporation significantly decreases the boron acceptor concentration in diamonds. Hall measurements at room temperature showed that the carriers concentration of the co-doped diamonds decreases, and the mobility increases obviously. The highest hole mobility of sample BNDD-1 reached 980 cm2·V-1·s-1, possible reasons were discussed in the paper.

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Understanding the synergistic effect of mixed solvent annealing on perovskite film formation Kun Qian(钱昆), Yu Li(李渝), Jingnan Song(宋静楠), Jazib Ali, Ming Zhang(张明), Lei Zhu(朱磊), Hong Ding(丁虹), Junzhe Zhan(詹俊哲), and Wei Feng(冯威) Chin. Phys. B, 2021, 30 (6):  068103.  DOI: 10.1088/1674-1056/abdb1f Abstract ( 569 )   HTML ( 2 )   PDF (1661KB) ( 100 )   Morphology control of perovskite films is of critical importance for high-performance photovoltaic devices. Although solvent vapor annealing (SVA) treatment has been widely used to improve the film quality efficiently, the detailed mechanism of film growth is still under construction, and there is still no consensus on the selection of solvents and volume for further optimization. Here, a series of solvents (DMF, DMSO, mixed DMF/DMSO) were opted for exploring their impact on fundamental structural and physical properties of perovskite films and the performance of corresponding devices. Mixed solvent SVA treatment resulted in unique benefits that integrated the advantages of each solvent, generating a champion device efficiency of 19.76% with improved humidity and thermal stability. The crystallization mechanism was constructed by conducting grazing-incidence wide-angle x-ray diffraction (GIWAXS) characterizations, showing that dissolution and recrystallization dominated the film formation. A proper choice of solvent and its volume balancing the two processes thus afforded the desired perovskite film. This study reveals the underlying process of film formation, paving the way to producing energy-harvesting materials in a controlled manner towards energy-efficient and stable perovskite-based devices.

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Morphologies of a spherical bimodal polyelectrolyte brush induced by polydispersity and solvent selectivity Qing-Hai Hao(郝清海) and Jie Cheng(成洁) Chin. Phys. B, 2021, 30 (6):  068201.  DOI: 10.1088/1674-1056/abd7d2 Abstract ( 358 )   HTML ( 1 )   PDF (1742KB) ( 67 )   It is commonly realized that polydispersity may significantly affect the surface modification properties of polymer brush systems. In light of this, we systematically study morphologies of bidisperse polyelectrolyte brush grafted onto a spherical nanocolloid in the presence of trivalent counterions using molecular dynamics simulations. Via varying polydispersity, grafting density, and solvent selectivity, the effects of electrostatic correlation and excluded volume are focused, and rich phase behaviors of binary mixed polyelectrolyte brush are predicted, including a variety of pinned-patch morphologies at low grafting density and micelle-like structures at high grafting density. To pinpoint the mechanism of surface structure formation, the shape factor of two species of polyelectrolyte chains and the pair correlation function between monomers from different polyelectrolyte ligands are analyzed carefully. Also, electrostatic correlations, manifested as the bridging through trivalent counterions, are examined by identifying four states of trivalent counterions. Our simulation results may be useful for designing smart stimuli-responsive materials based on mixed polyelectrolyte coated surfaces.

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Silicon micropillar electrodes of lithiumion batteries used for characterizing electrolyte additives Fangrong Hu(胡放荣), Mingyang Zhang(张铭扬), Wenbin Qi(起文斌), Jieyun Zheng(郑杰允), Yue Sun(孙悦), Jianyu Kang(康剑宇), Hailong Yu(俞海龙), Qiyu Wang(王其钰), Shijuan Chen(陈世娟), Xinhua Sun(孙新华), Baogang Quan(全保刚), Junjie Li(李俊杰), Changzhi Gu(顾长志), and Hong Li(李泓) Chin. Phys. B, 2021, 30 (6):  068202.  DOI: 10.1088/1674-1056/abf558 Abstract ( 579 )   HTML ( 3 )   PDF (2770KB) ( 208 )   The <100> crystal-oriented silicon micropillar array platforms were prepared by microfabrication processes for the purpose of electrolyte additive identification. The silicon micropillar array platform was used for the study of fluorinated vinyl carbonate (FEC), vinyl ethylene carbonate (VEC), ethylene sulfite (ES), and vinyl carbonate (VC) electrolyte additives in the LiPF6 dissolved in a mixture of ethylene carbonate and diethyl carbonate electrolyte system using charge/discharge cycles, electrochemical impedance spectroscopy, cyclic voltammetry, scanning electron microscopy, and x-ray photoelectron spectroscopy. The results show that the silicon pillar morphology displays cross-shaped expansion after lithiation/delithiation, the inorganic lithium salt keeps the silicon pillar morphology intact, and the organic lithium salt content promotes a rougher silicon pillar surface. The presence of poly-(VC) components on the surface of FEC and VC electrodes allows the silicon pillar to accommodate greater volume expansion while remaining intact. This work provides a standard, fast, and effective test method for the performance analysis of electrolyte additives and provides guidance for the development of new electrolyte additives.

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Suppression of ice nucleation in supercooled water under temperature gradients Li-Ping Wang(王利平), Wei-Liang Kong(孔维梁), Pei-Xiang Bian(边佩翔), Fu-Xin Wang(王福新), and Hong Liu(刘洪) Chin. Phys. B, 2021, 30 (6):  068203.  DOI: 10.1088/1674-1056/abd764 Abstract ( 522 )   HTML ( 3 )   PDF (1022KB) ( 59 )   Understanding the behaviours of ice nucleation in non-isothermal conditions is of great importance for the preparation and retention of supercooled water. Here ice nucleation in supercooled water under temperature gradients is analyzed thermodynamically based on classical nucleation theory (CNT). Given that the free energy barrier for nucleation is dependent on temperature, different from a uniform temperature usually used in CNT, an assumption of linear temperature distribution in the ice nucleus was made and taken into consideration in analysis. The critical radius of the ice nucleus for nucleation and the corresponding nucleation model in the presence of a temperature gradient were obtained. It is observed that the critical radius is determined not only by the degree of supercooling, the only dependence in CNT, but also by the temperature gradient and even the Young's contact angle. Effects of temperature gradient on the change in free energy, critical radius, nucleation barrier and nucleation rate with different contact angles and degrees of supercooling are illustrated successively. The results show that a temperature gradient will increase the nucleation barrier and decrease the nucleation rate, particularly in the cases of large contact angle and low degree of supercooling. In addition, there is a critical temperature gradient for a given degree of supercooling and contact angle, at the higher of which the nucleation can be suppressed completely.

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Suppression of ferroresonance using passive memristor emulator S Poornima Chin. Phys. B, 2021, 30 (6):  068401.  DOI: 10.1088/1674-1056/abd7e0 Abstract ( 361 )   HTML ( 1 )   PDF (928KB) ( 129 )   Power system inherently consists of capacitance and inductance in its components. Equipment with saturable inductance and circuit capacitance provides circumstances of generating ferroresonance, resulting in overvoltage and overcurrent in the connected system. The effects of ferroresonance result in insulation failure and hence damage to the equipment is unavoidable. Though many devices are proposed for mitigating such circumstances, a promising technology of using memristors may provide better performance than others in the future. A memristor emulator using the N-channel JFET J310 is used in this work. Unlike other electronic components that replicate memristor properties, the chosen memristor emulator is a passive device since it does not need any external power supply. Simulation and experimental results verify the design of a memristor emulator and the characteristics of an ideal memristor. Experimental results prove that the memristor emulator can suppress the fundamental ferroresonance induced in a prototype single phase transformer. The results of the harmonic analysis also validate the memristor performance against the conventional technique.

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SBT-memristor-based crossbar memory circuit Mei Guo(郭梅), Ren-Yuan Liu(刘任远), Ming-Long Dou(窦明龙), and Gang Dou(窦刚) Chin. Phys. B, 2021, 30 (6):  068402.  DOI: 10.1088/1674-1056/abd7dc Abstract ( 452 )   HTML ( 1 )   PDF (835KB) ( 149 )   Implementing memory using nonvolatile, low power, and nano-structure memristors has elicited widespread interest. In this paper, the SPICE model of Sr0.95Ba0.05TiO3 (SBT)-memristor was established and the corresponding characteristic was analyzed. Based on an SBT-memristor, the process of writing, reading, and rewriting of the binary and multi-value memory circuit was analyzed. Moreover, we verified the SBT-memristor-based 4×4 crossbar binary and multi-value memory circuits through comprehensive simulations, and analyzed the sneak-path current and memory density. Finally, we apply the 8×8 crossbar multi-value memory circuits to the images memory.

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Effect of electrical contact on performance of WSe2 field effect transistors Yi-Di Pang(庞奕荻), En-Xiu Wu(武恩秀), Zhi-Hao Xu(徐志昊), Xiao-Dong Hu(胡晓东), Sen Wu(吴森), Lin-Yan Xu(徐临燕), and Jing Liu(刘晶) Chin. Phys. B, 2021, 30 (6):  068501.  DOI: 10.1088/1674-1056/abd752 Abstract ( 583 )   HTML ( 4 )   PDF (1079KB) ( 169 )   Two-dimensional (2D) transition metal dichalcogenides (TMDCs) such as tungsten diselenide (WSe2) have spead many interesting physical properties, which may become ideal candidates to develop new generation electronic and optoelectronic devices. In order to reveal essential features of 2D TMDCs, it is necessary to fabricate high-quality devices with reliable electrical contact. We systematically analyze the effect of graphene and metal contacts on performance of multi-layered WSe2 field effect transistors (FETs). The temperature-dependent transport characteristics of both devices are tested. Only graphene-contacted WSe2 FETs are observed with the metal-insulator transition phenomenon which mainly attributes to the ultra-clean contact interface and lowered contact barrier. Further characterization on contact barrier demonstrates that graphene contact enables lower contact barrier with WSe2 than metal contact, since the Fermi level of graphene can be modulated by the gate bias to match the Fermi level of the channel material. We also analyze the carrier mobility of both devices under different temperatures, revealing that graphene contact can reduce the charge scattering of the device caused by ionized impurities and phonon vibrations in low and room temperature regions, respectively. This work is expected to provide reference for fabricating 2D material devices with decent performances.

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Reversible waveform conversion between microwave and optical fields in a hybrid opto-electromechanical system Hot! Li-Guo Qin(秦立国), Zhong-Yang Wang(王中阳), Jie-Hui Huang(黄接辉), Li-Jun Tian(田立君), and Shang-Qing Gong(龚尚庆) Chin. Phys. B, 2021, 30 (6):  068502.  DOI: 10.1088/1674-1056/abea8f Abstract ( 797 )   HTML ( 4 )   PDF (1493KB) ( 527 )   We present a scheme of reversible waveform conversion between microwave and optical fields in the hybrid opto-electromechanical system. As an intermediate interface, nanomechanical resonator optomechanically couples both optomechanical cavities in the optical and microwave frequency domains. We find the double-optomechanically induced transparency and achieve coherent signal waveform bi-directional transfer between microwave and optical fields based on quantum interference. In addition, we give an analytical expression of one-to-one correspondence between the microwave field and the optical output field, which intuitively shows the reversible waveform conversion relationship. In particular, by numerical simulations and approximate expression, we demonstrate the conversion effects of the three waveforms and discuss the bi-directional conversion efficiency and the bandwidth. such a hybrid opto- and electro-mechanical device has significant potential functions for electro-optic modulation and waveform conversion of quantum microwave-optical field in optical communications and further quantum networks.

SPECIAL TOPIC—Quantum computation and quantum simulation

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Fabrication and characterization of all-Nb lumped-element Josephson parametric amplifiers Hang Xue(薛航), Zhirong Lin(林志荣), Wenbing Jiang(江文兵), Zhengqi Niu(牛铮琦), Kuang Liu(刘匡), Wei Peng(彭炜), and Zhen Wang(王镇) Chin. Phys. B, 2021, 30 (6):  068503.  DOI: 10.1088/1674-1056/abeee6 Abstract ( 813 )   HTML ( 1 )   PDF (606KB) ( 269 )   Josephson parametric amplifiers (JPAs) with nearly quantum-limited noise performance have become indispensable devices for the measurements of superconducting quantum information. We have developed an all-Nb lumped-element flux-driven JPA operating in the three-wave mixing mode. Our Nb-based JPA comprises Nb/Al-AlOx/Nb Josephson junctions, a parallel-plate capacitor with SiO2 dielectric sandwiched between two Nb layers, a bottom coplanar waveguides layer, and a top Nb wiring layer. We experimentally demonstrate a 20 dB gain over a 190 MHz bandwidth, a mean 1 dB compression of -123 dBm, and near quantum-limited noise performance. This fabrication process can be further used to design impedance transformed parametric amplifiers for multiple-qubit readout.

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An easily-prepared impedance matched Josephson parametric amplifier Ya-Peng Lu(卢亚鹏), Quan Zuo(左权), Jia-Zheng Pan(潘佳政), Jun-Liang Jiang(江俊良), Xing-Yu Wei(魏兴雨), Zi-Shuo Li(李子硕), Wen-Qu Xu(许问渠), Kai-Xuan Zhang(张凯旋), Ting-Ting Guo(郭婷婷), Shuo Wang(王硕), Chun-Hai Cao(曹春海), Wei-Wei Xu(许伟伟), Guo-Zhu Sun(孙国柱), and Pei-Heng Wu(吴培亨) Chin. Phys. B, 2021, 30 (6):  068504.  DOI: 10.1088/1674-1056/ac0420 Abstract ( 801 )   HTML ( 9 )   PDF (1410KB) ( 609 )   An impedance matched parametric amplifier (IMPA) with Josephson junctions is fabricated and characterized. A hybrid structure containing coplanar and strip structures is implemented to realize an impedance taper line and a plate capacitor in an LC nonlinear resonator based on Josephson junctions. The upper plate of the capacitor is isolated with SiNx without grounding as well as the strips. Such easily-prepared designs greatly reduce the requirements for lithography alignment and precision, which makes the fabrication process more reliable. The experimental results show that in such IMPA a gain higher than 25 dB with a bandwidth of about 100 MHz can be obtained. This broadband amplifier operates close to the quantum limit. By adjusting the working point, a higher bandwidth of about 400 MHz can be obtained with a gain of about 17 dB.

INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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Gas sensor using gold doped copper oxide nanostructured thin films as modified cladding fiber Hussein T. Salloom, Rushdi I. Jasim, Nadir Fadhil Habubi, Sami Salman Chiad, M Jadan, and Jihad S. Addasi Chin. Phys. B, 2021, 30 (6):  068505.  DOI: 10.1088/1674-1056/abd2a7 Abstract ( 516 )   HTML ( 1 )   PDF (949KB) ( 140 )   We investigate the spectral response of nanostructured copper oxides thin film. Gold was doped in two different concentrations (2% and 4%) using the spray method. A novel ammonia gas sensor at various concentrations (0-500 ppm) was fabricated by replacing CuO films with a clad region. In addition, the effect of gold doping on structural, optical, and morphological properties has been demonstrated. The study shows that the spectral intensity increases linearly with ammonia concentration. The 4% Au doped CuO presents higher sensitivity compared with 2% doped and pure copper oxides. Time response characteristics of the sensor are also reported.

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Coarse-grained simulations on interactions between spectrins and phase-separated lipid bilayers Xuegui Lin(林雪桂), Xiaojie Chen(陈晓洁), and Qing Liang(梁清) Chin. Phys. B, 2021, 30 (6):  068701.  DOI: 10.1088/1674-1056/abf129 Abstract ( 439 )   HTML ( 1 )   PDF (15039KB) ( 252 )   Spectrin, the principal protein of the cytoskeleton of erythrocyte, plays a crucial role in the stability and flexibility of the plasma membrane of erythrocyte. In this work, we investigate the interactions between spectrins and phase-separated lipid bilayers using coarse-grained molecular dynamics simulation. We focus on the preference of spectrins with different lipids, the effects of the anionic lipids and the residue mutation on the interactions between spectrins and the lipid bilayers. The results indicate that spectrins prefer to contact with phosphatidylethanolamine (PE) lipids rather than with phosphatidylcholine (PC) lipids, and tend to contact with the liquid-disordered (Ld) domains enriched in unsaturated PE. Additionally, the anionic lipids, which show specific interaction with the positively charged or polar amino acids on the surface of the spectrins, can enhance the attraction between the spectrins and lipid domains. The mutation leads to the decrease of the structural stability of spectrins and increases the curvature of the lipid bilayer. This work provides some theoretical insights into understanding the erythrocyte structure and the mechanism of some blood diseases.

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Computational model investigating the effect of magnetic field on neural-astrocyte microcircuit Li-Cong Li(李利聪), Jin Zhou(周瑾), Hong-Ji Sun(孙洪吉), Peng Xiong(熊鹏), Hong-Rui Wang(王洪瑞), Xiu-Ling Liu(刘秀玲), and Chang-Yong Wang(王常勇) Chin. Phys. B, 2021, 30 (6):  068702.  DOI: 10.1088/1674-1056/abea81 Abstract ( 436 )   HTML ( 2 )   PDF (1461KB) ( 188 )   Extremely low-frequency magnetic field is widely used as a noninvasive stimulation method in clinical practice and basic research. Electrical field induced from magnetic pulse can decrease or increase neuronal electrical activity. However, the cellular mechanism underlying the effects of magnetic field is not clear from experimental data. Recent studies have demonstrated that "non-neuronal" cells, especially astrocytes, may be the potential effector for transcranial magnetic stimulation (TMS). In the present study, we implemented a neural-astrocyte microcircuit computational model based on hippocampal architecture to investigate the biological effects of different magnetic field frequencies on cells. The purpose of the present study is to elucidate the main influencing factors of MS to allow a better understanding of its mechanisms. Our model reproduced the basic characteristics of the neuron and astrocyte response to different magnetic stimulation. The results predict that interneurons with lower firing thresholds were more active in magnetic fields by contrast to pyramidal neurons. And the synaptic coupling strength between the connected neurons may be one of the critical factor to affect the effect of magnetic field on cells. In addition, the simulations show that astrocytes can decrease or increase slow inward currents (SICs) to finely tune neuronal excitation, which suggests their key role in excitatory-inhibitory balance. The interaction between neurons and astrocytes may represent a novel target for effective therapeutic strategies involving magnetic stimulation.

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Constraints on the kinetic energy of type-Ic supernova explosion from young PSR J1906+0746 in a double neutron star candidate Yi-Yan Yang(杨佚沿), Cheng-Min Zhang(张承民), Jian-Wei Zhang(张见微), and De-Hua Wang (王德华) Chin. Phys. B, 2021, 30 (6):  068703.  DOI: 10.1088/1674-1056/abda2c Abstract ( 480 )   HTML ( 1 )   PDF (622KB) ( 69 )   So far among the nineteen pairs of detected double neutron star (DNS) systems, it is a usual fact that the first-born recycled pulsar is detected, however the youngest DNS system PSR J1906+0746, with the characteristic age of 113 kyr, is one of the three detected DNS as a non-recycled and second-born NS, which is believed to be formed by an electron capture or a low energy ultra-stripped iron core-collapse supernova (SN) explosion. The SN remnant around PSR J1906+0746 is too dim to be observed by optical telescopes, then its x-ray flux limit has been given by Chandra. A reference pulsar PSR J1509-5850 with the young characteristic age of 154 kyr was chosen as an object of comparison, which has an SN remnant observed by Chandra and is believed to be formed by iron core SN explosion. We impose a restriction on the maximum kinetic energy of electron-capture (EC) SN explosion that induces the formation of PSR J1906+0746. The estimated result is (4-8)×1050 erg (1 erg=10-7 J), which is consistent with that of the published simulations of the EC process, i.e., a lower value than that of the conventional iron core SN explosion of (1-2)×1051 erg. As suggested, EC process for NS formation is pertained to the subluminous type Ic SN by the helium star with ONeMg core, thus for the first time we derived the kinetic energy of EC SN explosion of DNS, which may be reconciled with the recent observation of type Ic SN 2014ft with kinetic energy of 2×1050 erg.