17 September 2021, Volume 30 Issue 10
TOPICAL REVIEW—Topological 2D materials
 Two-dimensional topological semimetals Xiaolong Feng(冯晓龙), Jiaojiao Zhu(朱娇娇), Weikang Wu(吴维康), and Shengyuan A. Yang(杨声远) Chin. Phys. B, 2021, 30 (10):  107304.  DOI: 10.1088/1674-1056/ac1f0c Abstract ( 124 )   HTML ( 4 )   PDF (2835KB) ( 102 )   The field of two-dimensional topological semimetals, which emerged at the intersection of two-dimensional materials and topological materials, has been rapidly developing in recent years. In this article, we briefly review the progress in this field. Our focus is on the basic concepts and notions, in order to convey a coherent overview of the field. Some material examples are discussed to illustrate the concepts. We discuss the outstanding problems in the field that need to be addressed in future research.
TOPICAL REVIEW—Unconventional superconductivity
 A short review of the recent progresses in the study of the cuprate superconductivity Tao Li(李涛) Chin. Phys. B, 2021, 30 (10):  100508.  DOI: 10.1088/1674-1056/abfa04 Abstract ( 87 )   HTML ( 2 )   PDF (393KB) ( 70 )   The last 15 years have witnessed important progresses in our understanding of the mechanism of superconductivity in the high-Tc cuprates. There is now strong evidence that the strange metal behavior is induced by the quantum critical fluctuation at the pseudogap end point, where the Fermi surface changes its topology from hole-like to electron-like. However, experiments show that the quantum critical behavior in the high-Tc cuprates is qualitatively different from that observed in the heavy Fermion systems and the iron-based superconductors, in both of which the quantum critical behavior can be attributed to the quantum phase transition toward a symmetry breaking phase. The fact that the pseudogap exists as a spectral gap without a corresponding symmetry breaking order, together with the fact that the strange metal behavior occurs as a quantum critical behavior without a corresponding symmetry breaking phase transition, exposes the central difficulty of the field: the lack of a universal low energy effective theory description of the high-Tc phenomenology beyond the Landau paradigm. Recent experiments imply that the dualism between the local moment and the itinerant quasiparticle character of the electron in the high-Tc cuprates may serve as an organizing principle to go beyond the Landau paradigm and may hold the key to the mystery of the pseudogap phenomena and the strange metal behavior. It is the purpose of this review to provide an introduction to these recent progresses in the study of the high-Tc cuprate superconductors and their implications on the construction of a coherent picture for the high-Tc problem.
 Relevance of 3d multiplet structure in nickelate and cuprate superconductors Mi Jiang(蒋密) Chin. Phys. B, 2021, 30 (10):  107103.  DOI: 10.1088/1674-1056/abf646 Abstract ( 70 )   HTML ( 1 )   PDF (1661KB) ( 32 )   The recent discovery of superconductivity in doped rare-earth infinite-layer nickelates RNiO2, R=Nd, Pr as a new family of unconventional superconductors has inspired extensive research on their intriguing properties. One of the major motivation to explore the nickelate superconductors originated from their similarities with and differences from the cuprate superconductors, which have been extensively studied over the last decades but are still lack of the thorough understanding. In this short review, we summarized our recent investigation of the relevance of Ni/Cu-3d multiplet structure on the hole doped spin states in cuprate and recently discovered nickelate superconductors via an impurity model incorporating all the 3d orbitals. Further plausible explorations to be conducted are outlined as well. Our presented work provides an insightful framework for the investigation of the strongly correlated electronic systems in terms of the multiplet structure of transition metal compounds.
 A review of some new perspectives on the theory of superconducting Sr2RuO4 Wen Huang(黄文) Chin. Phys. B, 2021, 30 (10):  107403.  DOI: 10.1088/1674-1056/ac2488 Abstract ( 53 )   HTML ( 1 )   PDF (821KB) ( 25 )   The nature of the Cooper pairing in the paradigmatic unconventional superconductor Sr2RuO4 is an outstanding puzzle in condensed matter physics. Despite the tremendous efforts made in the past twenty-seven years, neither the pairing symmetry nor the underlying pairing mechanism in this material has been understood with clear consensus. This is largely due to the lack of a superconducting order that is capable of interpreting in a coherent manner the numerous essential experimental observations. At this stage, it may be desirable to reexamine our existing theoretical descriptions of superconducting Sr2RuO4. This review focuses on several recent developments that may provide some clues for future study. We highlight three separate aspects: 1) any pairing in the Eu symmetry channel, with which the widely discussed chiral p-wave is associated, shall acquire a 3D structure due to spin-orbit entanglement; 2) if the reported Kerr effect is a superconductivity-induced intrinsic bulk response, the superconductivity must either exhibit a chiral character, or be complex mixtures of certain set of helical p-wave pairings; 3) when expressed in a multiorbital basis, the Cooper pairing could acquire numerous exotic forms that are inaccessible in single-orbital descriptions. The implications of each of these new perspectives are briefly discussed in connection with selected experimental phenomena.
SPECIAL TOPIC—Unconventional superconductivity
 Theory of unconventional superconductivity in nickelate-based materials Ming Zhang(张铭), Yu Zhang(张渝), Huaiming Guo(郭怀明), and Fan Yang(杨帆) Chin. Phys. B, 2021, 30 (10):  108204.  DOI: 10.1088/1674-1056/ac0bb1 Abstract ( 64 )   HTML ( 1 )   PDF (4985KB) ( 29 )   Based on the two-band tight-binding model composed of the 3d orbital of Ni and the 5d orbital of R (=La), we used the random-phase-approximation method to study the pairing symmetry of the nickelate superconductors. It is found that even without considering the coupling between the R and Ni orbitals, neither the antiferromagnetic spin-fluctuation pattern nor the doping-dependent behavior of the robust dx2-y2-wave pairing state obtained in our calculations will be obviously influenced. Our results suggest the dominating role of the Ni 3d orbital in determining the low lying physics of the system. Furthermore, our results reveal a dome-shaped doping dependence of the superconducting transition temperature Tc, which is consistent with recent experiments.
SPECIAL TOPIC—Non-Hermitian physics
 Geometry of time-dependent $\mathcal{PT}$-symmetric quantum mechanics Da-Jian Zhang(张大剑), Qing-hai Wang(王清海), and Jiangbin Gong(龚江滨) Chin. Phys. B, 2021, 30 (10):  100307.  DOI: 10.1088/1674-1056/ac0ba8 Abstract ( 116 )   HTML ( 1 )   PDF (527KB) ( 90 )   A new type of quantum theory known as time-dependent $\mathcal{PT}$-symmetric quantum mechanics has received much attention recently. It has a conceptually intriguing feature of equipping the Hilbert space of a $\mathcal{PT}$-symmetric system with a time-varying inner product. In this work, we explore the geometry of time-dependent $\mathcal{PT}$-symmetric quantum mechanics. We find that a geometric phase can emerge naturally from the cyclic evolution of a $\mathcal{PT}$-symmetric system, and further formulate a series of related differential-geometry concepts, including connection, curvature, parallel transport, metric tensor, and quantum geometric tensor. These findings constitute a useful, perhaps indispensible, tool to investigate geometric properties of $\mathcal{PT}$-symmetric systems with time-varying system's parameters. To exemplify the application of our findings, we show that the unconventional geometric phase [Phys. Rev. Lett. 91 187902 (2003)], which is the sum of a geometric phase and a dynamical phase proportional to the geometric phase, can be expressed as a single geometric phase unveiled in this work.
 Non-Hermitian quasicrystal in dimerized lattices Longwen Zhou(周龙文) and Wenqian Han(韩雯岍) Chin. Phys. B, 2021, 30 (10):  100308.  DOI: 10.1088/1674-1056/ac1efc Abstract ( 101 )   HTML ( 0 )   PDF (3116KB) ( 60 )   Non-Hermitian quasicrystals possess $\mathcal{PT}$ and metal-insulator transitions induced by gain and loss or nonreciprocal effects. In this work, we uncover the nature of localization transitions in a generalized Aubry-André-Harper model with dimerized hopping amplitudes and complex onsite potential. By investigating the spectrum, adjacent gap ratios and inverse participation ratios, we find an extended phase, a localized phase and a mobility edge phase, which are originated from the interplay between hopping dimerizations and non-Hermitian onsite potential. The lower and upper bounds of the mobility edge are further characterized by a pair of topological winding numbers, which undergo quantized jumps at the boundaries between different phases. Our discoveries thus unveil the richness of topological and transport phenomena in dimerized non-Hermitian quasicrystals.
 Observation of the exceptional point in superconducting qubit with dissipation controlled by parametric modulation Zhan Wang(王战), Zhongcheng Xiang(相忠诚), Tong Liu(刘桐), Xiaohui Song(宋小会), Pengtao Song(宋鹏涛), Xueyi Guo(郭学仪), Luhong Su(苏鹭红), He Zhang(张贺), Yanjing Du(杜燕京), and Dongning Zheng(郑东宁) Chin. Phys. B, 2021, 30 (10):  100309.  DOI: 10.1088/1674-1056/ac0520 Abstract ( 62 )   HTML ( 0 )   PDF (2956KB) ( 41 )   Open physical systems described by the non-Hermitian Hamiltonian with parity-time-reversal (PT) symmetry show peculiar phenomena, such as the presence of an exceptional point (EP) at which the PT symmetry is broken and two resonant modes of the Hamiltonian become degenerate. Near the EP, the system could be more sensitive to external perturbations and this may lead to enhanced sensing. In this paper, we present experimental results on the observation of PT symmetry broken transition and the EP using a tunable superconducting qubit. The quantum system of investigation is formed by the two levels of the qubit and the energy loss of the system to the environment is controlled by a method of parametric modulation of the qubit frequency. This method is simple with no requirements for additional elements or qubit device modifications. We believe it can be easily implemented on multi-qubit devices that would be suitable for further exploration of non-Hermitian physics in more complex and diverse systems.
SPECIAL TOPIC—Ion beam modification of materials and applications
 Oxygen vacancies and V co-doped Co3O4 prepared by ion implantation boosts oxygen evolution catalysis Bo Sun(孙博), Dong He(贺栋), Hongbo Wang(王宏博), Jiangchao Liu(刘江超), Zunjian Ke(柯尊健), Li Cheng(程莉), and Xiangheng Xiao(肖湘衡) Chin. Phys. B, 2021, 30 (10):  106102.  DOI: 10.1088/1674-1056/ac1339 Abstract ( 70 )   HTML ( 2 )   PDF (2255KB) ( 30 )   Introducing heteroatoms and defects is a significant strategy to improve oxygen evolution reaction (OER) performance of electrocatalysts. However, the synergistic interaction of the heteroatom and defect still needs further investigations. Herein, we demonstrated an oxygen vacancy-rich vanadium-doped Co3O4 (V-Ov-Co3O4), fabricated by V-ion implantation, could be used for high-efficient OER catalysis. X-ray photoelectron spectra (XPS) and density functional theory (DFT) calculations show that the charge density of Co atom increased, and the reaction barrier of reaction pathway from O* to HOO* decreased. V-Ov-Co3O4 catalyst shows a low overpotential of 329 mV to maintain current density of 10 mA·cm-2, and a small Tafel slope of 74.5 mV·dec-1. This modification provides us with valuable perception for future design of heteroatom-doped and defect-based electrocatalysts.
 Investigations on ion implantation-induced strain in rotated Y-cut LiNbO3 and LiTaO3 Zhongxu Li(李忠旭), Kai Huang(黄凯), Yanda Ji(吉彦达), Yang Chen(陈阳), Xiaomeng Zhao(赵晓蒙), Min Zhou(周民), Tiangui You(游天桂), Shibin Zhang(张师斌), and Xin Ou(欧欣) Chin. Phys. B, 2021, 30 (10):  106103.  DOI: 10.1088/1674-1056/ac1416 Abstract ( 53 )   HTML ( 0 )   PDF (1033KB) ( 44 )   The monocrystalline LiNbO3 (LN) and LiTaO3 (LT) plates have been qualified as a kind of material platform for high performance RF filter that is considerable for the 5G communication. LN and LT thin films are usually transferred on handle wafers by combining ion-slicing and wafer bonding technique to form a piezoelectric on insulator (POI) substrate. The ion implantation is a key process and the implantation-induced strain is essential for the layer transfer. Here, we reported the strain profile of ion implanted rotated Y-cut LN and LT. The ion implantation generates the out-of-plane tensile strain of the sample surface and (006) plane, while both the tensile and compressive strain are observed on the (030) plane. The implanted ions redistributed due to the anisotropy of LN and LT, and induce the main tensile normal to the (006) plane. Meanwhile, the (030) planes are contracted due to the Poisson effect with the interstitial ions disturbing and mainly show a compressive strain profile.
 Hydrogen isotopic replacement and microstructure evolution in zirconium deuteride implanted by 150 keV protons Man Zhao(赵嫚), Mingxu Zhang(张明旭), Tao Wang(王韬), Jiangtao Zhao(赵江涛), Pan Dong(董攀), Zhen Yang(杨振), and Tieshan Wang(王铁山) Chin. Phys. B, 2021, 30 (10):  106104.  DOI: 10.1088/1674-1056/ac29a7 Abstract ( 54 )   HTML ( 0 )   PDF (1722KB) ( 31 )   Zirconium tritiated (ZrTx) is an alternative target material for deuteron-triton (D-T) reaction neutron generator. The isotopic replacement and microstructure evolution induced by hydrogen isotope implantation could significantly affect the performance of the target film. In this work, the zirconium deuteride film deposited on Mo/Si substrate was implanted by 150 keV protons with fluence from 1×1016 to 1×1018 protons/cm2. After implantation, the depth profiles of retained hydrogen (H) and deuterium (D) in these target films were analyzed by elastic recoil detection analysis (ERDA), and time of flight-secondary ion mass spectrometry (ToF-SIMS). Additionally, the microstructure evolution was also observed by x-ray diffraction (XRD) and scanning electron microscope (SEM). The D concentration in the ZrDx film decreased versus the proton implantation fluence. An analytical model was proposed to describe the hydrogen isotopic trapping and exchange as functions of incident protons fluence. Additionally, the XRD analysis revealed that no new phase was formed after proton implantation. Furthermore, circular flakings were observed on the ZrDx surface from SEM images at fluence up to 1×1018 protons/cm2, and this surface morphology was considered to associate with the hydrogen atoms congregation in Mo/Si boundary.
 Irradiation behavior and recovery effect of ferroelectric properties of PZT thin films Yu Zhao(赵瑜), Wen-Yue Zhao(赵文悦), Dan-Dan Ju(琚丹丹), Yue-Yue Yao(姚月月), Hao Wang(王豪), Cheng-Yue Sun(孙承月), Ya-Zhou Peng(彭亚洲), Yi-Yong Wu(吴宜勇), and Wei-Dong Fei(费维栋) Chin. Phys. B, 2021, 30 (10):  107702.  DOI: 10.1088/1674-1056/ac0dad Abstract ( 53 )   HTML ( 0 )   PDF (721KB) ( 31 )   Lead zirconate titanate piezoelectric ceramics have important applications in space and aerospace technology, but the effect and physical mechanism of charged particle radiation on their performance yet to be clarified. In this study, we characterized PbZr0.52Ti0.48O3 (PZT) thin films, and changes in the ferroelectric properties of the films before and after electron and proton irradiation were investigated. The natural and heat treatment recoverability of the ferroelectric properties were studied, and the damages and mechanisms of different types of radiation in PZT films were also investigated. The results show that, in addition to ionization damages, electron irradiation causes certain structural damage on the PZT film, and the large structural damage caused by proton irradiation reduces drastically the ferroelectricity of the PZT film.
REVIEW
 Progress in functional studies of transition metal borides Teng Ma(马腾), Pinwen Zhu(朱品文), and Xiaohui Yu(于晓辉) Chin. Phys. B, 2021, 30 (10):  108103.  DOI: 10.1088/1674-1056/ac1925 Abstract ( 59 )   HTML ( 0 )   PDF (2372KB) ( 39 )   In recent years, transition metal borides (TMBs) have attracted much attention because they are considered as potential superhard materials and have more abundant crystal structures compared with traditional superhard materials. So far, however, no superhard materials have been found in TMBs. A large number of structures and potential new properties in TMBs are induced by the various hybridization ways of boron atoms and the high valence electrons of transition metals, which provide many possibilities for its application. And most TMBs have layered structures, which make TMBs have the potential to be a two-dimensional (2D) material. The 2D materials have novel properties, but the research on 2D TMBs is still nearly blank. In this paper, the research progress of TMBs is summarized involving structure, mechanical properties, and multifunctional properties. The strong covalent bonds of boron atoms in TMBs can form one-dimensional, two-dimensional, and three-dimensional substructures, and the multiple electron transfer between transition metal and boron leads to a variety of chemical bonds in TMBs, which are the keys to obtain high hardness and multifunctional properties of TMBs. Further research on the multifunctional properties of TMBs, such as superconductors, catalysts, and high hardness ferromagnetic materials, is of great significance to the discovery of new multifunctional hard materials.
RAPID COMMUNICATION
 Widely tunable single-photon source with high spectral-purity from telecom wavelength to mid-infrared wavelength based on MgO:PPLN Hot! Chang-Wei Sun(孙昌伟), Yu Sun(孙宇), Jia-Chen Duan(端家晨), Guang-Tai Xue(薛广太), Yi-Chen Liu(刘奕辰), Liang-Liang Lu(陆亮亮), Qun-Yong Zhang(张群永), Yan-Xiao Gong(龚彦晓), Ping Xu(徐平), and Shi-Ning Zhu(祝世宁) Chin. Phys. B, 2021, 30 (10):  100312.  DOI: 10.1088/1674-1056/ac20cb Abstract ( 491 )   HTML ( 0 )   PDF (1543KB) ( 544 )   By utilizing the extended phase-matching (EPM) method, we investigate the generation of single photons with high spectral-purity in a magnesium-doped periodically-poled lithium niobate (MgO:PPLN) crystal via the spontaneous parametric down-conversion (SPDC) process. By adjusting the temperature and pump wavelength, the wavelength of the single photons can be tuned from telecom to mid-infrared (MIR) wavelengths, for which the spectral-purity can be above 0.95 with high transmission filters. In experiments, we engineer a MgO:PPLN with poling period of 20.35 μ which emits the EPM photon pair centered at 1496.6 nm and 1644.0 nm and carry out the joint spectral intensity (JSI) and Glauber's second-order self-correlation measurements to characterize the spectral purity. The results are in good agreement with the numerical simulations. Our work may provide a valuable approach for the generation of spectrally pure single photons at a wide range of wavelengths which is competent for various photonic quantum technologies.
 Peculiar diffusion behavior of AlCl4 intercalated in graphite from nanosecond-long molecular dynamics simulations Qianpeng Wang(王乾鹏), Daye Zheng(郑大也), Lixin He(何力新), and Xinguo Ren(任新国) Chin. Phys. B, 2021, 30 (10):  107102.  DOI: 10.1088/1674-1056/ac0692 Abstract ( 53 )   HTML ( 1 )   PDF (888KB) ( 29 )   The diffusion property of the intercalated species in the graphite materials is at the heart of the rate performance of graphite-based metal-ion secondary battery. Here we study the diffusion process of a AlCl4 molecule within graphite – a key component of a recently reported aluminum ion battery with excellent performance – via molecular dynamics (MD) simulations. Both ab-initio MD (AIMD) and semiempirical tight-binding MD simulations show that the diffusion process of the intercalated AlCl4 molecule becomes rather inhomogeneous, when the simulation time exceeds approximately 100 picoseconds. Specifically, during its migration in between graphene layers, the intercalated AlCl4 molecule may become stagnant occasionally, and then recovers its normal (fast) diffusion behavior after halting for a while. When this phenomenon occurs, the linear relationship of the mean squared displacement (MSD) versus the duration time is not fulfilled. We interpret this peculiar behavior as a manifestation of inadequate sampling of rare event (the stagnation of the molecule), which does not yet appear in short-time MD simulations. We further check the influence of strains present in graphite intercalated compounds (GIC) on the diffusion properties of AlCl4, and find that their presence in general slows down the diffusion of the intercalated molecule, and is detrimental to the rate performance of the GIC-based battery.
GENERAL
 High winding number of topological phase in non-unitary periodic quantum walk Yali Jia(贾雅利) and Zhi-Jian Li(李志坚) Chin. Phys. B, 2021, 30 (10):  100301.  DOI: 10.1088/1674-1056/abf554 Abstract ( 80 )   HTML ( 0 )   PDF (2063KB) ( 44 )   Topological phases and their associated multiple edge states are studied by constructing a one-dimensional non-unitary multi-period quantum walk with parity-time symmetry. It is shown that large topological numbers can be obtained when choosing an appropriate time frame. The maximum value of the winding number can reach the number of periods in the one-step evolution operator. The validity of the bulk-edge correspondence is confirmed, while for an odd-period quantum walk and an even-period quantum walk, they have different configurations of the 0-energy edge state and π-energy edge state. On the boundary, two kinds of edge states always coexist in equal amount for the odd-period quantum walk, however three cases including equal amount, unequal amount or even only one type may occur for the even-period quantum walk.
 Detection of spin current through a quantum dot with Majorana bound states Ning Wang(王宁), Xingtao An(安兴涛), and Shuhui Lv(吕树慧) Chin. Phys. B, 2021, 30 (10):  100302.  DOI: 10.1088/1674-1056/abff1c Abstract ( 53 )   HTML ( 0 )   PDF (564KB) ( 17 )   The spin transport properties are theoretically investigated when a quantum dot (QD) is side-coupled to Majorana bound states (MBSs) driven by a symmetric dipolar spin battery. It is found that MBSs have a great effect on spin transport properties. The peak-to-valley ratio of the spin current decreases as the coupling strength between the MBS and the QD increases. Moreover, a non-zero charge current with two resonance peaks appears in the system. In the extreme case where the dot-MBS coupling strength is strong enough, the spin current and the charge current are both constants in the non-resonance peak range. When considering the effect of the Zeeman energy, it is interesting that the resonance peak at the higher energy appears one shoulder. And the shoulder turns into a peak when the Zeeman energy is big enough. In addition, the coupling strength between the two MBSs weakens their effects on the currents of the system. These results are helpful for understanding the MBSs signature in the transport spectra.
 Measurement-device-independent quantum dialogue Guo-Fang Shi(石国芳) Chin. Phys. B, 2021, 30 (10):  100303.  DOI: 10.1088/1674-1056/ac140a Abstract ( 48 )   HTML ( 0 )   PDF (590KB) ( 10 )   Recently, measurement-device-independent quantum secure direct communication schemes were proposed by Niu et al. [Sci. Bull. 63 1345 (2018)] and Zhou et al. [Sci. China-Phys. Mech. Astron. 63 230362 (2020)]. Inspired by their ideas, in this paper, a measurement-device-independent quantum dialogue protocol based on entanglement is designed and proven to be secure. The advantage of this scheme is that it can not only allow two communicators to transmit secret messages between each other, making the application scenarios more extensive, but can also eliminate all the security loopholes related to the measurement device and information leakage. In terms of experimental implementation, the scheme mainly involves the preparation of entangled states, the preparation of single photons, quantum storage, Bell measurement and other technologies, all of which are mature at present, therefore, the scheme is feasible by using current technologies.
 Fabrication and characterization of superconducting multiqubit device with niobium base layer Feifan Su(宿非凡), Zhaohua Yang(杨钊华), Shoukuan Zhao(赵寿宽), Haisheng Yan(严海生), Ziting Wang(王子婷), Xiaohui Song(宋小会), Ye Tian(田野), and Shiping Zhao(赵士平) Chin. Phys. B, 2021, 30 (10):  100304.  DOI: 10.1088/1674-1056/ac11d7 Abstract ( 82 )   HTML ( 0 )   PDF (1348KB) ( 46 )   Superconducting transmon qubits are the leading platform in solid-state quantum computing and quantum simulation applications. In this work, we develop a fabrication process for the transmon multiqubit device with a niobium base layer, shadow-evaporated Josephson junctions, and airbridges across the qubit control lines to suppress crosstalk. Our results show that these multiqubit devices have well-characterized readout resonators, and that the energy relaxation and Ramsey (spin-echo) dephasing times are up to ～ 40 μs and 14 (47) μs, respectively. We perform single-qubit gate operations that demonstrate a maximum gate fidelity of 99.97%. In addition, two-qubit vacuum Rabi oscillations are measured to evaluate the coupling strength between qubits, and the crosstalk among qubits is found to be less than 1% with the fabricated airbridges. Further improvements in qubit coherence performance using this fabrication process are also discussed.
 Fulde-Ferrell-Larkin-Ovchinnikov states in equally populated Fermi gases in a two-dimensional moving optical lattice Jin-Ge Chen(陈金鸽), Yue-Ran Shi(石悦然), Ren Zhang(张仁), Kui-Yi Gao(高奎意), and Wei Zhang(张威) Chin. Phys. B, 2021, 30 (10):  100305.  DOI: 10.1088/1674-1056/abf346 Abstract ( 30 )   HTML ( 0 )   PDF (1142KB) ( 10 )   We study the possibility of stabilizing a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state in an equally populated two-component Fermi gas trapped in a moving two-dimensional optical lattice. For a system with nearly half filling, we find that a finite pairing momentum perpendicular to the moving direction can be spontaneously induced for a proper choice of lattice velocity. As a result, the total pairing momentum is tilted towards the nesting vector to take advantage of the significant enhancement of the density of states.
 Detection of the quantum states containingat most k-1 unentangled particles Yan Hong(宏艳), Xianfei Qi(祁先飞), Ting Gao(高亭), and Fengli Yan(闫凤利) Chin. Phys. B, 2021, 30 (10):  100306.  DOI: 10.1088/1674-1056/abfb5e Abstract ( 74 )   HTML ( 0 )   PDF (537KB) ( 47 )   There are many different classifications of entanglement for multipartite quantum systems, one of which is based on the number of the unentangled particles. In this paper, we mainly study the quantum states containing at most k-1 unentangled particles and provide several entanglement criteria based on the different forms of inequalities, which can both identify quantum states containing at most k-1 unentangled particles. We show that these criteria are more effective for some states by concrete examples.
 Optimized monogamy and polygamy inequalities for multipartite qubit entanglement Jia-Bin Zhang(张嘉斌), Zhi-Xiang Jin(靳志祥), Shao-Ming Fei(费少明), and Zhi-Xi Wang(王志玺) Chin. Phys. B, 2021, 30 (10):  100310.  DOI: 10.1088/1674-1056/abf12e Abstract ( 71 )   HTML ( 0 )   PDF (583KB) ( 27 )   We investigate the monogamy and polygamy inequalities of arbitrary multipartite quantum states, and provide new classes of monogamy and polygamy inequalities of multiqubit entanglement in terms of concurrence, entanglement of formation, negativity, and Tsallis-q entanglement, respectively. We show that these new monogamy and polygamy inequality relations are tighter than the existing ones with detailed examples.
 Preparation of spin squeezed state in SiV centers coupled by diamond waveguide Yong-Hong Ma(马永红), Yuan Xu(许媛), Quan-Zhen Ding(丁全振), and Yu-Sui Chen(陈予遂) Chin. Phys. B, 2021, 30 (10):  100311.  DOI: 10.1088/1674-1056/ac05b3 Abstract ( 42 )   HTML ( 0 )   PDF (996KB) ( 15 )   Spin squeezing is a fascinating manifestation of many-particle entanglement and one of the most promising quantum resources. In this paper, we propose a novel realization of a solid-state quantum spin squeezing by applying SiV centers embedded in a diamond waveguide with the help of a microwave field. The phenomena about the generation of spin squeezing are analyzed numerically in Markovian environments. Our analysis shows that spin squeezing can be generated with the microwave field's help under some realistic conditions, despite the presence of dephasing and mechanical damping. This solid-state spin squeezing based on SiV centers in diamonds might be applied to magnetometers, interferometry, and other precise measurements.
 Control of firing activities in thermosensitive neuron by activating excitatory autapse Ying Xu(徐莹) and Jun Ma(马军) Chin. Phys. B, 2021, 30 (10):  100501.  DOI: 10.1088/1674-1056/abeeef Abstract ( 44 )   HTML ( 0 )   PDF (1529KB) ( 27 )   Temperature has distinct influence on the activation of ion channels and the excitability of neurons, and careful change in temperature can induce possible mode transition in the neural activities. The formation and development of autapse connection to neuron can enhance its self-adaption to external stimulus, and thus the firing patterns in neuron can be controlled effectively. The autapse is activated to drive a thermosensitive neuron, which is developed from the FitzHugh-Nagumo neural circuit by incorporating a thermistor, and the dynamics in the neural activities is explored to find mode dependence on the temperature and autaptic current. It is found that the firing modes can be controlled by temperature, and the neuron is wakened from resting state to periodic oscillation with the increase of temperature. Furthermore, the intensity and the intrinsic time delay in the autapse are respectively adjusted to control the neural activities, and it is confirmed that appropriate setting for autaptic current can balance and enhance the temperature effect on the neural activities.
 Dynamics analysis of a 5-dimensional hyperchaotic system with conservative flows under perturbation Xuenan Peng(彭雪楠), Yicheng Zeng(曾以成), and Qi Xie(谢奇) Chin. Phys. B, 2021, 30 (10):  100502.  DOI: 10.1088/1674-1056/abea9a Abstract ( 55 )   HTML ( 0 )   PDF (5686KB) ( 38 )   Conservative chaotic flows have better ergodicity, therefore researching dynamics and applications of conservative systems has become a hot topic. We introduce a constant-perturbation into a 5-dimensional (5D) conservative model. Consequently, the line equilibria of original model have been changed to non-equilibrium. Plentiful chaos phenomena such as coexisting conservative flows can be observed in this modified system. In addition, by increasing the magnitude of the disturbance, the conservative system can be transformed to a dissipative system. Then, the modified system is realized by an xc7z020clg400 field programmable gate array (FPGA) chip. The designed chaotic oscillator consumes fewer resources and has high iteration speed. Finally, a pseudo random number generator based on this novel digital oscillator is designed.
 Adaptive synchronization of chaotic systems with less measurement and actuation Shun-Jie Li(李顺杰), Ya-Wen Wu(吴雅文), and Gang Zheng(郑刚) Chin. Phys. B, 2021, 30 (10):  100503.  DOI: 10.1088/1674-1056/abec33 Abstract ( 34 )   HTML ( 0 )   PDF (501KB) ( 12 )   We investigate the synchronization problem between identical chaotic systems only when necessary measurement (output) and actuation (input) are needed to be implemented by the adaptive controllers. A sufficient condition is derived based on the Lyapunov stability theory and Schur complementary lemma. Moreover, the theoretic result is applied to the Rikitake system and the hyperchaotic Liu system to show its effectiveness and correctness. Numerical simulations are presented to verify the results.
 Cooperative behaviors of coupled nonidentical oscillators with the same equilibrium points Wen Sun(孙文), Biwen Li(李必文), Wanli Guo(郭万里), Zhigang Zheng(郑志刚), and Shihua Chen(陈士华) Chin. Phys. B, 2021, 30 (10):  100504.  DOI: 10.1088/1674-1056/abf101 Abstract ( 36 )   HTML ( 0 )   PDF (1643KB) ( 17 )   The cooperative behaviors resulted from the interaction of coupled identical oscillators have been investigated intensively. However, the coupled oscillators in practice are nonidentical, and there exist mismatched parameters. It has been proved that under certain conditions, complete synchronization can take place in coupled nonidentical oscillators with the same equilibrium points, yet other cooperative behaviors are not addressed. In this paper, we further consider two coupled nonidentical oscillators with the same equilibrium points, where one oscillator is convergent while the other is chaotic, and explore their cooperative behaviors. We find that the coupling mode and the coupling strength can bring the coupled oscillators to different cooperation behaviors in unidirectional or undirected couplings. In the case of directed coupling, death islands appear in two-parameter spaces. The mechanism inducing these transitions is presented.
 Application of the edge of chaos in combinatorial optimization Yanqing Tang(唐彦卿), Nayue Zhang(张娜月), Ping Zhu(朱萍), Minghu Fang(方明虎), and Guoguang He(何国光) Chin. Phys. B, 2021, 30 (10):  100505.  DOI: 10.1088/1674-1056/abff40 Abstract ( 35 )   HTML ( 0 )   PDF (818KB) ( 10 )   Many problems in science, engineering and real life are related to the combinatorial optimization. However, many combinatorial optimization problems belong to a class of the NP-hard problems, and their globally optimal solutions are usually difficult to solve. Therefore, great attention has been attracted to the algorithms of searching the globally optimal solution or near-optimal solution for the combinatorial optimization problems. As a typical combinatorial optimization problem, the traveling salesman problem (TSP) often serves as a touchstone for novel approaches. It has been found that natural systems, particularly brain nervous systems, work at the critical region between order and disorder, namely, on the edge of chaos. In this work, an algorithm for the combinatorial optimization problems is proposed based on the neural networks on the edge of chaos (ECNN). The algorithm is then applied to TSPs of 10 cities, 21 cities, 48 cities and 70 cities. The results show that ECNN algorithm has strong ability to drive the networks away from local minimums. Compared with the transiently chaotic neural network (TCNN), the stochastic chaotic neural network (SCNN) algorithms and other optimization algorithms, much higher rates of globally optimal solutions and near-optimal solutions are obtained with ECNN algorithm. To conclude, our algorithm provides an effective way for solving the combinatorial optimization problems.
 Design and multistability analysis of five-value memristor-based chaotic system with hidden attractors Li-Lian Huang(黄丽莲), Shuai Liu(刘帅), Jian-Hong Xiang(项建弘), and Lin-Yu Wang(王霖郁) Chin. Phys. B, 2021, 30 (10):  100506.  DOI: 10.1088/1674-1056/ac1e13 Abstract ( 61 )   HTML ( 0 )   PDF (9991KB) ( 62 )   A five-value memristor model is proposed, it is proved that the model has a typical hysteresis loop by analyzing the relationship between voltage and current. Then, based on the classical Liu-Chen system, a new memristor-based four-dimensional (4D) chaotic system is designed by using the five-value memristor. The trajectory phase diagram, Poincare mapping, bifurcation diagram, and Lyapunov exponent spectrum are drawn by numerical simulation. It is found that, in addition to the general chaos characteristics, the system has some special phenomena, such as hidden homogenous multistabilities, hidden heterogeneous multistabilities, and hidden super-multistabilities. Finally, according to the dimensionless equation of the system, the circuit model of the system is built and simulated. The results are consistent with the numerical simulation results, which proves the physical realizability of the five-value memristor-based chaotic system proposed in this paper.
 Heterogeneous traffic flow modeling with drivers' timid and aggressive characteristics Cong Zhai(翟聪), Weitiao Wu(巫威眺), and Songwen Luo(罗淞文) Chin. Phys. B, 2021, 30 (10):  100507.  DOI: 10.1088/1674-1056/abf7ae Abstract ( 45 )   HTML ( 0 )   PDF (9379KB) ( 25 )   The driver's characteristics (e.g., timid and aggressive) has been proven to greatly affect the traffic flow performance, whereas the underlying assumption in most of the existing studies is that all drivers are homogeneous. In the real traffic environment, the drivers are distinct due to a variety of factors such as personality characteristics. To better reflect the reality, we introduce the penetration rate to describe the degree of drivers' heterogeneity (i.e., timid and aggressive), and proceed to propose a generalized heterogeneous car-following model with different driver's characteristics. Through the linear stability analysis, the stability conditions of the proposed heterogeneous traffic flow model are obtained based on the perturbation method. The impacts of the penetration rate of drivers with low intensity, the average value and standard deviation of intensity parameters characterizing two types of drivers on the stability of traffic flow are analyzed by simulation. Results show that higher penetration of aggressive drivers contributes to traffic flow stability. The average value has a great impact on the stability of traffic flow, whereas the impact of the standard deviation is trivial.
 Breathers and solitons for the coupled nonlinear Schrödinger system in three-spine α-helical protein Xiao-Min Wang(王晓敏) and Peng-Fei Li(李鹏飞) Chin. Phys. B, 2021, 30 (10):  100509.  DOI: 10.1088/1674-1056/ac132f Abstract ( 39 )   HTML ( 0 )   PDF (21037KB) ( 23 )   We mainly investigate the variable-coefficient 3-coupled nonlinear Schrödinger (NLS) system, which describes soliton dynamics in the three-spine α-helical protein with inhomogeneous effect. The variable-coefficient NLS equation is transformed into the constant coefficient NLS equation by similarity transformation firstly. The Hirota method is used to solve the constant coefficient NLS equation, and then we get the one- and two-breather solutions of the variable-coefficient NLS equation. The results show that, in the background of plane waves and periodic waves, the breather can be transformed into some forms of combined soliton solutions. The influence of different parameters on the soliton solution and the collision between two solitons are discussed by some graphs in detail. Our results are helpful to study the soliton dynamics in α-helical protein.
 Collective motion of polar active particles on a sphere Yi Chen(陈奕), Jun Huang(黄竣), Fan-Hua Meng(孟繁华), Teng-Chao Li(李腾超), and Bao-Quan Ai(艾保全) Chin. Phys. B, 2021, 30 (10):  100510.  DOI: 10.1088/1674-1056/abfccf Abstract ( 67 )   HTML ( 0 )   PDF (5225KB) ( 41 )   Collective motion of active particles with polar alignment is investigated on a sphere. We discussed the factors that affect particle swarm motion and define an order parameter that can show the degree of particle swarm motion. In the model, we added a polar alignment strength, along with Gaussian curvature, affecting particles swarm motion. We find that when the force exceeds a certain limit, the order parameter will decrease with the increase of the force. Combined with our definition of order parameter and observation of the model, the reason is that particles begin to move side by side under the influence of polar forces. In addition, the effects of velocity, rotational diffusion coefficient, and packing fraction on particle swarm motion are discussed. It is found that the rotational diffusion coefficient and the packing fraction have a great influence on the clustering motion of particles, while the velocity has little influence on the clustering motion of particles.
 LnCu3(OH)6Cl3 (Ln = Gd, Tb, Dy): Heavy lanthanides on spin-1/2 kagome magnets Hot! Ying Fu(付盈), Lianglong Huang(黄良龙), Xuefeng Zhou(周雪峰), Jian Chen(陈见), Xinyuan Zhang(张馨元), Pengyun Chen(陈鹏允), Shanmin Wang(王善民), Cai Liu(刘才), Dapeng Yu(俞大鹏), Hai-Feng Li(李海峰), Le Wang(王乐), and Jia-Wei Mei(梅佳伟) Chin. Phys. B, 2021, 30 (10):  100601.  DOI: 10.1088/1674-1056/ac1e20 Abstract ( 211 )   HTML ( 0 )   PDF (1887KB) ( 182 )   The spin-1/2 kagome antiferromagnets are key prototype materials for studying frustrated magnetism. Three isostructural kagome antiferromagnets LnCu3(OH)6Cl3 (Ln = Gd, Tb, Dy) have been successfully synthesized by the hydrothermal method. LnCu3(OH)6Cl3 adopts space group P3m1 and features the layered Cu-kagome lattice with lanthanide Ln3+ cations sitting at the center of the hexagons. Although heavy lanthanides (Ln = Gd, Tb, Dy) in LnCu3(OH)6Cl3 provide a large effective magnetic moment and ferromagnetic-like spin correlations compared to light-lanthanides (Nd, Sm, Eu) analogues, Cu-kagome holds an antiferromagnetically ordered state at around 17 K like YCu3(OH)6Cl3.
 Cascaded dual-channel fiber SPR temperature sensor based on liquid and solid encapsulations Yong Wei(魏勇), Lingling Li(李玲玲), Chunlan Liu(刘春兰), Jiangxi Hu(胡江西), Yudong Su(苏于东), Ping Wu(吴萍), and Xiaoling Zhao(赵晓玲) Chin. Phys. B, 2021, 30 (10):  100701.  DOI: 10.1088/1674-1056/ac0426 Abstract ( 49 )   HTML ( 0 )   PDF (4079KB) ( 17 )   In order to control the working wavelength range of the fiber surface plasmon resonance (SPR) temperature sensor and realize the wavelength division multiplexing type multi-channel fiber SPR temperature sensor, by comprehensively investigating the influence of liquids with different thermal-optical coefficients and solid packaging materials on the performance of fiber SPR temperature sensor, a dual-channel fiber SPR temperature sensor based on liquid-solid cascade encapsulation was designed and fabricated. The liquid temperature sensing stage encapsulated in capillary worked in 616.03 nm-639.05 nm band, the solid sensing stage coated with pouring sealant worked in 719.37 nm-825.27 nm band, and the two stages were cascaded to form a fiber dual-channel temperature sensor. The testing results indicated that when the temperature range was 35 ℃-95 ℃, the sensitivity of two-stage temperature detection was -0.384 nm/℃ and -1.765 nm/℃ respectively. The proposed fiber sensor has simple fabrication and excellent performance which can be widely used in various fields of dual-channel temperature measurement and temperature compensation.
ATOMIC AND MOLECULAR PHYSICS
 Density functional theory study of formaldehyde adsorption and decomposition on Co-doped defective CeO2 (110) surface Yajing Zhang(张亚婧), Keke Song(宋可可), Shuo Cao(曹硕), Xiaodong Jian(建晓东), and Ping Qian(钱萍) Chin. Phys. B, 2021, 30 (10):  103101.  DOI: 10.1088/1674-1056/abff42 Abstract ( 88 )   HTML ( 0 )   PDF (1866KB) ( 26 )   Formaldehyde as an air pollutant to adverse health effects for humanity has been getting attention. The adsorption and dissociation of formaldehyde (HCHO) on the CoxCe1-xO2-δ (110) surface were investigated by the density functional theory (DFT) calculations. We calculated the oxygen vacancy formation energy as the function of its site around dopant Co in detail. The results showed that Co doping was accompanied by compensating oxygen hole spontaneous formation. The adsorption configurations and bindings of HCHO at different locations on the CoxCe1-xO2 (110) were presented. Four possible pathways of oxidation of formaldehyde on the catalytic surface were explored. The results suggested that formaldehyde dissociation at different adsorption sites on the doped CeO2 (110) – first forming dioxymethylene (CH2O2) intermediate, and then decomposing into H2O, H2, CO2, and CO molecules. It was found that the presence of cobalt and oxygen vacancy significantly prompted the surface activity of CeO2.
ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
 Electrostatic force of dust deposition originating from contact between particles and photovoltaic glass Xing-Cai Li(李兴财), Juan Wang(王娟), and Guo-Qing Su(苏国庆) Chin. Phys. B, 2021, 30 (10):  104101.  DOI: 10.1088/1674-1056/abeb12 Abstract ( 38 )   HTML ( 0 )   PDF (2940KB) ( 8 )   Charged photovoltaic glass produces an electrostatic field. The electrostatic field exerts an electrostatic force on dust particles, thus making more dust particles deposited on the glass. In this paper, the contact electrification between the deposited dust particles and the photovoltaic glass is studied. Meanwhile, the surface charge density model of the photovoltaic glass and the electrostatic force of charged particles are analyzed. The results show that with the increasing of the particle impact speed and the inclination angle of the photovoltaic panel, the charges on particles increase to different degrees. Under a given condition, the electrostatic forces acting on the charged particles at different positions above the glass plate form a bell-shaped distribution at a macro level, and present a maximum value in the center of the plate. As the distance between the particle and the charged glass decreases, the electrostatic force exerted on the particle increases significantly and fluctuates greatly. However, its mean value is still higher than the force caused by gravity and the adhesion force, reported by some studies. Therefore, we suggest that photovoltaic glass panels used in the severe wind-sand environment should be made of an anti-static transparent material, which can lessen the dust particles accumulated on the panels.
 Wideband radar cross section reduction based on absorptive coding metasurface with compound stealth mechanism Xinmi Yang(杨歆汨), Changrong Liu(刘昌荣), Bo Hou(侯波), and Xiaoyang Zhou(周小阳) Chin. Phys. B, 2021, 30 (10):  104102.  DOI: 10.1088/1674-1056/abf110 Abstract ( 49 )   HTML ( 0 )   PDF (2406KB) ( 16 )   A scheme of combing wave absorption and phase cancellation mechanisms for widening radar cross section (RCS) reduction band is proposed. An absorptive coding metasurface implementing this scheme is derived from traditional circuit analog absorber (CAA) composed of resistive ring elements which characterize dual resonances behavior. It is constructed by replacing some of the CAA elements by another kind of resistive ring elements which is singly resonant in between the original two resonant bands and has reflection phase opposite to that of the original elements at resonance. Hence the developed metasurface achieves an improved low-RCS band over which the lower and higher sub-bands are mainly contributed by wave absorption mainly while the middle sub-band is formed by joint effect of wave absorption and anti-phase cancellation mechanisms. The polarization-independent wideband RCS reduction property of the metasurface is validated by full-wave simulation results of a preliminary and an advanced design examples which employ the same element configuration but different element layout schemes as partitioned distribution and random coding. The advanced design also exhibits broadband bistatic low-RCS property and keeps a stable specular RCS reduction performance with regard to incident elevation angle up to 35°. The advanced design is fabricated and the experimental results of the sample agrees qualitatively well with their simulated counterparts. The measured figure of merit (i.e., low-RCS bandwidth ratio versus electrical thickness) of the sample is 40.572, which is superior to or comparable with those for most of other existing metasurface with compound RCS reduction mechanism. The proposed compound metasurface technique also features simple structure, light weight, low cost and easy fabrication compared with other techniques. This makes it promising in applications such as radar stealth and electromagnetic compatibility.
 Physical properties of relativistic electron beam during long-range propagation in space plasma environment Bi-Xi Xue(薛碧曦), Jian-Hong Hao(郝建红), Qiang Zhao(赵强), Fang Zhang(张芳), Jie-Qing Fan(范杰清), and Zhi-Wei Dong(董志伟) Chin. Phys. B, 2021, 30 (10):  104103.  DOI: 10.1088/1674-1056/ac192f Abstract ( 54 )   HTML ( 0 )   PDF (32373KB) ( 225 )   It is known that ion channel can effectively limit the radial expansion of an artificial electron beam during its long-range propagation in the space plasma environment. Most prior studies discussed the focusing characteristics of the beam in the ion channel, but the establishment process and transient properties of the ion channel itself, which also plays a crucial role during the propagation of the relativistic electron beam in the plasma environment, were commonly neglected. In this study, a series of two-dimensional (2D) particle-in-cell simulations is performed and an analytical model of ion channel oscillation is constructed according to the single-particle motion. The results showed that when the beam density is higher than the density of plasma environment, ion channel can be established and always continues to oscillate periodically over the entire propagation. Multiple factors, including the beam electron density, initial beam radius, and the plasma density can affect the oscillation properties of ion channel. Axial velocity of the beam oscillates synchronously with the ion channel and this phenomenon will finally develop into a two-stream instability which can seriously affect the effective transport for relativistic electron beam. Choosing appropriate beam parameters based on various plasma environments may contribute to the improvement of the stability of ion channel. Additionally, radial expansion of the beam can be limited by ion channel and a stable long-range propagation in terrestrial atmosphere may be achieved.
 Tunable characteristic of phase-locked quantum cascade laser arrays Zeng-Hui Gu(顾增辉), Jin-Chuan Zhang(张锦川), Huan Wang(王欢), Peng-Chang Yang(杨鹏昌), Ning Zhuo(卓宁), Shen-Qiang Zhai(翟慎强), Jun-Qi Liu(刘俊岐), Li-Jun Wang(王利军), Shu-Man Liu(刘舒曼), Feng-Qi Liu(刘峰奇), and Zhan-Guo Wang(王占国) Chin. Phys. B, 2021, 30 (10):  104201.  DOI: 10.1088/1674-1056/abec30 Abstract ( 59 )   HTML ( 0 )   PDF (1428KB) ( 30 )   A multimode interference (MMI) structure is designed to simplify the fabrication of quantum cascade laser (QCL) phase-locked arrays. The MMI geometry is optimized with a sufficient output channel distance to accommodate conventional photolithography and wet etching process by which power amplifier array is fabricated without using the complicated two-step etching-regrowth or dry etching technique. The far-field pattern with periodically modulated peaks reveals that the beams from the arrays are phase-locked. Furthermore, the frequency tuning performance of the MMI-based phase-locked arrays is studied using the Littrow-configuration external cavity structure. A wavelength tuning range of more than 60 cm-1 is demonstrated, which will eventually realize the high power, frequency tunable, large-scale phase-locked arrays, and their application in spectroscopy.
 Phase-shift interferometry measured transmission matrix of turbid medium: Three-step phase-shifting interference better than four-step one Xi-Cheng Zhang(张熙程), Zuo-Gang Yang(杨佐刚), Long-Jie Fang(方龙杰), Jing-Lei Du(杜惊雷), Zhi-You Zhang(张志友), and Fu-Hua Gao(高福华) Chin. Phys. B, 2021, 30 (10):  104202.  DOI: 10.1088/1674-1056/abe92a Abstract ( 40 )   HTML ( 0 )   PDF (3481KB) ( 21 )   Transmission matrix (TM) is an important tool for controlling light focusing, imaging, and communication through turbid media. It can be measured by 3-step (TM3) or 4-step (TM4) phase-shifting interference, but the similarities and differences of the transmission matrices obtained by the two methods are rarely reported. Therefore, we make a quantitative comparison of the peak light intensity, signal-to-noise ratio, and average background of 24×24 = 576 focal points between paired samples (TM3-TM4) through the Wilcoxon rank sum test, and discuss the singular value of the transmission matrix and the focal peak. The comparative results of peak light intensity and signal-to-noise ratio show that there is a significant difference between the 3-step phase shift and the 4-step phase shift transmission matrixes. The focusing effect of the former is significantly better than that of the latter; interest concentrates on the focal intensity and singular value. The reciprocal of the singular value is proportional to the squared intensity, which is in accordance with singular value theory. The results of comparison of peak light intensity and signal-to-noise ratio strongly suggest that 3-step phase shift should be selected and used in applying the phase shift method to the measurement of the transmission matrix; and the singular value is of great significance in quantifying the focusing, imaging, and communication quality of the transmission matrix.
 Settled fast measurement of topological charge by direct extraction of plane wave from vortex beam Xiao-Bo Yang(杨晓波) and Jin Hu(胡进) Chin. Phys. B, 2021, 30 (10):  104203.  DOI: 10.1088/1674-1056/abec32 Abstract ( 35 )   HTML ( 0 )   PDF (4363KB) ( 7 )   A method of measuring the vortex beam topological charge (TC) is proposed based on a device that can directly extract the plane wave form from the vortex beam in which the different propagation angles of the plane waves are uniquely related to the different TCs. Then the TC can be obtained by simply comparing the energy values perceived by two fixed sensors in the detection location with the help of twin omnidirectional energy absorbers (OEAs). Because the settled detection relies only on the simple quantitative value at two fixed positions, neither pattern recognition nor field analysis procedure is applied, thus allowing faster measurement. Some features of the methodology are investigated, and the numerical simulations verify the feasibility and robustness of the system.
 Fano interference and transparency in a waveguide-nanocavity hybrid system with an auxiliary cavity Yu-Xin Shu(树宇鑫), Xiao-San Ma(马小三), Xian-Shan Huang(黄仙山), Mu-Tian Cheng(程木田), and Jun-Bo Han(韩俊波) Chin. Phys. B, 2021, 30 (10):  104204.  DOI: 10.1088/1674-1056/ac041e Abstract ( 30 )   HTML ( 0 )   PDF (615KB) ( 9 )   We investigate theoretically single photon transport in one-dimensional waveguide coupled to a pair of cavities, which are denoted by the first cavity and the auxiliary cavity. Two cases with no atom and one atom embedded in the first cavity are discussed. The Fano dips in the transmission spectrum and locations of transparency window are calculated. When no atom is embedded in the first cavity, there exists a transparency window under the condition that the first cavity and the auxiliary cavity are not resonant. The locations of the transparency window and Fano line type depend strongly on the eigen frequency of the auxiliary cavity and the coupling strength between the auxiliary cavity and the waveguide. When one atom is embedded in the first cavity, we show that the transparency window exists even though the first cavity, the atom and the auxiliary cavity are resonant. The Fano line type is strongly dependent on the eigen frequency of the auxiliary cavity and the coupling strength. Our results have potential applications in design of quantum devices at the level of single photon, such as single photon switch and single photon routers.
 Variation of electron density in spectral broadening process in solid thin plates at 400 nm Si-Yuan Xu(许思源), Yi-Tan Gao(高亦谈), Xiao-Xian Zhu(朱孝先), Kun Zhao(赵昆), Jiang-Feng Zhu(朱江峰), and Zhi-Yi Wei(魏志义) Chin. Phys. B, 2021, 30 (10):  104205.  DOI: 10.1088/1674-1056/abf0fe Abstract ( 37 )   HTML ( 0 )   PDF (691KB) ( 18 )   The generation of continuous spectrum centered at 400 nm from solid thin plates is demonstrated in this work. A continuum covering 365 nm to 445 nm is obtained when 125-μJ frequency-doubled Ti:sapphire laser pulses are applied to six thin fused silica plates at 1-kHz repetition rate. The generalized nonlinear Schrödinger equation simplified for forward propagation is solved numerically, the spectral broadening with the experimental parameters is simulated, and good agreement between simulated result and experimental measurement is achieved. The variation of electron density in the thin plate and the advantage of a low electron density in the spectral broadening process are discussed.
 Collapse arrest in the space-fractional Schrödinger equation with an optical lattice Manna Chen(陈曼娜), Hongcheng Wang(王红成), Hai Ye(叶海), Xiaoyuan Huang(黄晓园), Ye Liu(刘晔), Sumei Hu(胡素梅), and Wei Hu(胡巍) Chin. Phys. B, 2021, 30 (10):  104206.  DOI: 10.1088/1674-1056/abefc8 Abstract ( 41 )   HTML ( 0 )   PDF (1450KB) ( 9 )   The soliton solution and collapse arrest are investigated in the one-dimensional space-fractional Schrödinger equation with Kerr nonlinearity and optical lattice. The approximate analytical soliton solutions are obtained based on the variational approach, which provides reasonable accuracy. Linear-stability analysis shows that all the solitons are linearly stable. No collapses are found when the Lévy index 1<α≤2. For α=1, the collapse is arrested by the lattice potential when the amplitude of perturbations is small enough. It is numerically proved that the energy criterion of collapse suppression in the two-dimensional traditional Schrödinger equation still holds in the one-dimensional fractional Schrödinger equation. The physical mechanism for collapse prohibition is also given.
 Enhancing light absorption for organic solar cells using front ITO nanograting and back ultrathin Al layer Li Zhang(张力), Wei-Ning Liu(刘卫宁), Yan-Zhou Wang(王艳周), Qi-Ming Liu(刘奇明), Jun-Shuai Li(栗军帅), Ya-Li Li(李亚丽), and De-Yan He(贺德衍) Chin. Phys. B, 2021, 30 (10):  104207.  DOI: 10.1088/1674-1056/abe92c Abstract ( 38 )   HTML ( 0 )   PDF (2563KB) ( 10 )   To address the discrepancy between carrier collection and light absorption of organic solar cells caused by the limited carrier mobility and optical absorption coefficient for the normally employed organic photoactive layers, a light management structure composed of a front indium tin oxide (ITO) nanograting and ultrathin Al layer inserted in between the photoactive layer and the electron transport layer (ETL) is introduced. Owing to the antireflection and light scattering induced by the ITO nanograting and the suppression of light absorption in the ETL by the inserted Al layer, the light absorption of the photoactive layer is significantly enhanced in a spectral range from 400 nm to 650 nm that also covers the main energy region of solar irradiation for the normally employed active materials such as the P3HT:PC61BM blend. The simulation results indicate that comparing with the control device with a planar configuration of ITO/PEDOT:PSS/P3HT:PC61BM (80-nm thick)/ZnO/Al, the short-circuit current density and power conversion efficiency of the optimized light management structure can be improved by 32.86% and 34.46%. Moreover, good omnidirectional light management is observed for the proposed device structure. Owing to the fact that the light management structure possesses the simple structure and excellent performance, the exploration of such a structure can be believed to be significant in fabricating the thin film-based optoelectronic devices.
 Generation of a large orbital angular momentum beam via an optical fiber winding around a curved path and its application Wei-Han Tan(谭维翰), Chao-Ying Zhao(赵超樱), Yi-Chao Meng(孟义朝), and Qi-Zhi Guo(郭奇志) Chin. Phys. B, 2021, 30 (10):  104208.  DOI: 10.1088/1674-1056/abefc9 Abstract ( 39 )   HTML ( 0 )   PDF (5854KB) ( 15 )   Many papers have been published on the study of orbital angular momentum (OAM) of the laser modes based on the Laguerre-Gaussian (LG) beam and helical phase plate or rotating cylindrical lens, and the principal ray of the LG beam remains straight line. These ways are difficult to get a large OAM modes. In this paper, we propose a novel method to prepare a large OAM modes when the light propagates through a optical fiber winding around a curved path, and establish a theoretical framework based on the principal ray path changing. Firstly, we investigate three kinds of winding structure. Secondly, based on the analytical solutions and numerical calculations, we can find that the spiral body can achieve a large OAM temporal pulse. At the same time, based on the zero OAM diffraction diagram, we can obtain an improvement of resolving power beyond Rayleigh's criterion. Finally, applying a large OAM diffraction pattern to realize 12-bitencodes, we can obtain a high-security optical information transfer system.
 Phase matched scanning optical parametric chirped pulse amplification based on pump beam deflection Rong Ye(叶荣), Huining Dong(董会宁), Xianyun Wu(吴显云), and Xiang Gao(高翔) Chin. Phys. B, 2021, 30 (10):  104209.  DOI: 10.1088/1674-1056/abfbda Abstract ( 22 )   HTML ( 0 )   PDF (575KB) ( 7 )   Combined with the optical beam deflection, a novel approach of phase matched broadband scanning optical parametric chirped pulse amplification (OPCPA) was proposed. For this scheme, there was no superfluous operations to the chirped signal pulse which propagated in a changeless direction straightforward, but the pump beam were deflected in space with time by passing through a KTN crystal, which was applied with varied driving voltage. The theories of phase matching of each chirped signal frequency based on pump beam deflection was analyzed detailedly. And the type-I amplification of chirped signal with 800 nm central wavelength and 20 nm bandwidth pumped by 532 nm in BBO crystal was simulated as a case in point. The simulation results showed that the spectral distribution of chirped signal pulse was almost the same as the initial form, i.e., there was nearly no narrowing on the amplified spectrum by using of the scanning OPCPA based on pump beam deflection. In addition, the simulations demonstrated that it was worth minimizing the voltage deviation applied to KTN crystal as much as possible for the sake of better waveform, larger bandwidth and higher conversion efficiency of amplified signal pulse in the proposed scanning OPCPA.
 Novel high-quality Fano resonance based on metal-insulator-metal waveguide with L-shaped resonators Changsong Wu(伍长松) and Jun Zhu(朱君) Chin. Phys. B, 2021, 30 (10):  104210.  DOI: 10.1088/1674-1056/abf922 Abstract ( 32 )   HTML ( 0 )   PDF (860KB) ( 14 )   Developing a convenient method that can be routinely applied for ascertaining proportions of different vegetable oils employed in commercial blended edible oils remains a significant challenge. We address this issue by proposing a novel method for detecting volume fraction of different oils based on the fact that these oils are optically transparent and have slightly different indices of refraction at a given temperature and wavelength. Accordingly, we develop a highly sensitive sensor for measuring the index of refraction of oil blends based on Fano resonance spectra obtained using a metal-insulator-metal (MIM) waveguide structure comprising a gapped straight waveguide coupled with two L-shaped resonators. The index of refraction sensitivity and figure of merit of the structure are calculated based on modeling using the finite element method, and the waveguide structure is accordingly optimized by adjusting the different geometric parameters to achieve a high-quality Fano resonance spectrum. The optimized structure achieves an ultra-high refractive index sensitivity of 770 nm/RIU in terms of a refractive index unit (RIU) of 1. Moreover, a highly stable linear relationship is obtained between the refractive index of mixed edible oils and the resonance wavelength. Experimental results demonstrate that the proposed structure can detect slight changes in the volume fractions of the components in blended oils.
 Ideal optomechanically induced transparency generation in a cavity optoelectromechanical system Jing Wang(王婧) and Xue-Dong Tian(田雪冬) Chin. Phys. B, 2021, 30 (10):  104211.  DOI: 10.1088/1674-1056/ac1924 Abstract ( 56 )   HTML ( 0 )   PDF (2177KB) ( 32 )   The ideal optomechanically induced transparency effects of an output probe field are investigated in a cavity optoelectromechanical system, which is composed of an optical cavity, a charged mechanical resonator, and a charged object. Although the charged mechanical resonator damping rate is nonzero, the ideal optomechanically induced transparency can still appear due to the non-rotating wave approximation effect in the system. The location of optomechanically induced transparency dip can be controlled via the Coulomb coupling strength. In addition, we find that both the transparency window width and the maximum dispersion curve slope are closely related to the optical cavity decay rate.
 Repulsive bubble-bubble interaction in ultrasonic field Ling-Ling Zhang(张玲玲), Wei-Zhong Chen(陈伟中), Yao-Rong Wu(武耀蓉), Yang Shen(沈阳), and Guo-Ying Zhao(赵帼英) Chin. Phys. B, 2021, 30 (10):  104301.  DOI: 10.1088/1674-1056/abea98 Abstract ( 34 )   HTML ( 0 )   PDF (818KB) ( 19 )   The bubble-bubble interaction (BBI) is attractive in most cases, but also could be repulsive. In the present study, three specific mechanisms of repulsive BBI are given. The great contribution to the repulsive BBI is derived from the large radius of the bubble catching the rebound point of the other bubble. For “elastic” bubble and “inelastic” bubble, with the increase of the phase shift between two bubbles, the BBI changes from attractive to repulsive, and the repulsion can be maintained. For both “elastic” bubbles, the BBI alternates between attractive interaction and repulsive interaction along the direction where the ambient radius of one of bubbles increases. For stimulating bubble and stimulated bubble, the BBI can be repulsive. Its property depends on the ambient radii of bubbles. In addition, the distribution of the radiation forces in ambient radius space shows that the BBI is sensitive to the size of bubble and is complex because the bubbles are not of the same size in an ultrasonic field. Finally, as the distance increases or decreases monotonically with time, the absolute value of the BBI decreases or increases, correspondingly. The BBI can oscillate not only in strength but also in polarity when the distance fluctuates with time.
 Numerical simulation of acoustic field under mechanical stirring Jin-He Liu(刘金河), Zhuang-Zhi Shen(沈壮志), and Shu-Yu Lin(林书玉) Chin. Phys. B, 2021, 30 (10):  104302.  DOI: 10.1088/1674-1056/abf4bb Abstract ( 42 )   HTML ( 0 )   PDF (19156KB) ( 23 )   The present study analyzes the effect of stirring on ultrasonic degradation experiments through acoustic field distribution, which provides a guidance for further improvement of the degradation rate of organic solutions. It is known that in order to eliminate the standing wave field formed by ultrasonic radiation in the water tank, the liquid in the water tank needs to be stirred and the corresponding distribution of acoustic field is simulated by using the finite element method (FEM). The standing wave leads to an uneven distribution of the acoustic field when it is not stirred, and disappears after being stirred, which increases the cavitation area in the ultrasonic cleaning tank. Then, the degradation experiment with agitation is carried out. The experimental results show that the degradation rate of the solution is higher than that when there is no agitation, which confirms the importance of the acoustic field distribution to ultrasonic degradation. In addition, it is clear that with the increase of the stirring speed, the degradation rate increases first and reaches a maximum at 600 rpm before decreasing. Finally, the distribution of flow field is simulated and analyzed.
 Lattice Boltzmann simulation on thermal performance of composite phase change material based on Voronoi models Meng-Yue Guo(郭孟月), Qun Han(韩群), Xiang-Dong Liu(刘向东), and Bo Zhou(周博) Chin. Phys. B, 2021, 30 (10):  104401.  DOI: 10.1088/1674-1056/ac041d Abstract ( 37 )   HTML ( 0 )   PDF (3979KB) ( 17 )   Phase change materials (PCMs) are important for sustaining energy development. For the thermal performance enhancement, the composite PCM with metal foam reconstructed by the Voronoi method is investigated in this work. The lattice Boltzmann method (LBM) is used to analyze the melting process on a pore scale. The melting interface evolution and temperature contour of the composite PCM are explored and compared with those of pure PCM. Moreover, structure parameters including the pore density, porosity and irregularity are investigated comprehensively, indicating that the additive of metal foam strengthens the melting performance of PCM obviously. Compared with pure PCM, the composite PCM has quick rates of the melting front evolution and heat transfer. The heat conduction plays a great role in the whole melting process since the convection is weakened for the composite PCM. To improve the melting efficiency, a larger pore density and smaller irregularity are recommended in general. More significantly, a suitable porosity is determined based on the requirement for the balance between the melting rate and heat storage capacity in practical engineering.
 Hierarchical lichee-like Fe3O4 assemblies and their high heating efficiency in magnetic hyperthermia Wen-Yu Li(李文宇), Wen-Tao Li(李文涛), Bang-Quan Li(李榜全), Li-Juan Dong(董丽娟), Tian-Hua Meng(孟田华), Ge Huo(霍格), Gong-Ying Liang(梁工英), and Xue-Gang Lu(卢学刚) Chin. Phys. B, 2021, 30 (10):  104402.  DOI: 10.1088/1674-1056/ac0789 Abstract ( 36 )   HTML ( 0 )   PDF (1092KB) ( 6 )   A nontoxic and biocompatible thermoseed is developed for the magnetic hyperthermia. Two kinds of thermoseed materials: hierarchical hollow and solid lichee-like Fe3O4 assemblies, are synthesized by a facile hydrothermal method. The crystal structure of Fe3O4 assemblies are characterized by x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Moreover, the prepared Fe3O4 assemblies are used as a magnetic heat treatment agent, and their heating efficiency is investigated. Compared to solid assembly, hollow lichee-like Fe3O4 assembly exhibits a higher specific absorption rate of 116.53 W/g and a shorter heating time, which is ascribed to its higher saturation magnetization, larger initial particle size, and the unique hierarchical hollow structure. Furthermore, the magnetothermal effect is primarily attributed to Néel relaxation. Overall, we propose a facile and convenient approach to enhance the heating efficiency of magnetic nanoparticles by forming hollow hierarchical assemblies.
 Characterization of size effect of natural convection in melting process of phase change material in square cavity Shi-Hao Cao(曹世豪) and Hui Wang(王辉) Chin. Phys. B, 2021, 30 (10):  104403.  DOI: 10.1088/1674-1056/abea9c Abstract ( 39 )   HTML ( 1 )   PDF (3374KB) ( 7 )   The accelerating effect of natural convection on the melting of phase change material (PCM) has been extensively demonstrated. However, such an influence is directly dependent on the size and shape of domain in which phase change happens, and how to quantitatively describe such an influence is still challenging. On the other hand, the simulation of natural convection process is considerably difficult, involving complex fluid flow in a region changing with time, and is typically not operable in practice. To overcome these obstacles, the present study aims to quantitatively investigate the size effect of natural convection in the melting process of PCM paraffin filled in a square latent heat storage system through experiment and simulation, and ultimately a correlation equation to represent its contribution is proposed. Firstly, the paraffin melting experiment is conducted to validate the two-dimensional finite element model based on the enthalpy method. Subsequently, a comprehensive investigation is performed numerically for various domain sizes. The results show that the melting behavior of paraffin is dominated by the thermal convection. When the melting time exceeds 50 s, a whirlpoor flow caused by natural convection appears in the upper liquid phase region close to the heating wall, and then its influencing range gradually increases to accelerate the melting of paraffin. However, its intensity gradually decreases as the distance between the melting front and the heating wall increases. Besides, it is found that the correlation between the total melting time and the domain size approximately exhibits a power law. When the domain size is less than 2 mm, the accelerating effect of natural convection becomes very weak and can be ignored in practice. Moreover, in order to simplify the complex calculation of natural convection, the equivalent thermal conductivity concept is proposed to include the contribution of natural convection to the total melting time, and an empirical correlation is given for engineering applications.
 Comparative investigation of microjetting generated from monocrystalline tin surface and polycrystalline tin surface under plane impact loading Shao-Wei Sun(孙少伟), Guan-Qing Tang(汤观晴), Ya-Fei Huang(黄亚飞), Liang-Zhi Cao(曹良志), and Xiao-Ping Ouyang(欧阳晓平) Chin. Phys. B, 2021, 30 (10):  104701.  DOI: 10.1088/1674-1056/abeeea Abstract ( 34 )   HTML ( 0 )   PDF (3347KB) ( 6 )   With considering the scattering effect of grain boundary and the grain orientation, the molecular dynamics is used for the first time to comparatively investigate microjetting generated by monocrystalline tin surface and polycrystalline tin surface under plane impact loading in this work. The research results show that when the impact velocity is low, the scattering effect of grain boundary and different grain orientations in a polycrystalline tin will cause the sample to melt inhomogeneously, leading the shock wave front to attenuate, meanwhile, the inhomogeneous melting can result in jet deviating. Comparing with monocrystalline tin, the jet head velocity, jet velocity coefficient, and jet mass coefficient of polycrystalline tin at low impact velocity are all low. Moreover, as the impact velocity increases, this influence decreases and the microjetting results of polycrystalline tin and monocrystalline tin tend to be consistent with each other.
 Analysis of natural frequency for imaging interface in liquid lens Na Xie(谢娜) Chin. Phys. B, 2021, 30 (10):  104702.  DOI: 10.1088/1674-1056/ac229c Abstract ( 52 )   HTML ( 0 )   PDF (569KB) ( 27 )   Transmission beam can be modulated at the liquid-liquid interface inside an electrowetting liquid lens. The fluctuation characteristics of the interface has a decisive effect on the beam modulation. A closed cylinder in capillary constant scale is analyzed and the natural frequencies of a flat interface are obtained using capillary wave hydrodynamics. Results in modes 0 and 1 are in good agreement with previous experiments in the literature. The influences of the radius, the height ratio and the height-to-diameter ratio of a liquid lens on the interface eigenfrequencies are analyzed.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
 Optimization of the beam quality in ionization injection by a tailoring gas profile Ye Cui(崔野), Guo-Bo Zhang(张国博), Yan-Yun Ma(马燕云), Xiao-Hu Yang(杨晓虎), Jia-Yin Mu(牟佳胤), Hai-Bo Yao(姚海波), Ming Zi(资明), Jie Zhou(周洁), Jing-Qi Yang(杨静琦), Li-Xiang Hu(胡理想), and Li-Chao Tian(田立朝) Chin. Phys. B, 2021, 30 (10):  105201.  DOI: 10.1088/1674-1056/ac1b89 Abstract ( 57 )   HTML ( 0 )   PDF (1118KB) ( 46 )   A new scheme is proposed to improve the electron beam quality of ionization-induced injection by tailoring gas profile in laser wakefield acceleration. Two-dimensional particle-in-cell simulations show that the ionization-induced injection mainly occurs in high-density stage and automatically truncates in low-density stage due to the decrease of the wakefield potential difference. The beam loading can be compensated by the elongated beam resulting from the density transition stage. The beam quality can be improved by shorter injection distance and beam loading effect. A quasi-monoenergetic electron beam with a central energy of 258 MeV and an energy spread of 5.1% is obtained under certain laser-plasma conditions.
 Multibeam Raman amplification of a finite-duration seed in a short distance Y G Chen(陈雨谷), Y Chen(陈勇), S X Xie(谢善秀), N Peng(彭娜), J Q Yu(余金清), and C Z Xiao(肖成卓) Chin. Phys. B, 2021, 30 (10):  105202.  DOI: 10.1088/1674-1056/ac0521 Abstract ( 53 )   HTML ( 0 )   PDF (1336KB) ( 24 )   A new scheme of multibeam Raman amplification (MRA) is proposed in virtue of the collective mode by sharing a common scattered light. Multiple laser beams can provide a higher growth rate, but the overlapping region limits the amplification length. We suggest to use a finite-duration seed to facilitate MRA in a short distance. Through two-dimensional particle-in-cell simulations, we find that two-beam Raman amplification has a much higher growth rate than that of single-beam one. This growth rate depends on the initial seed amplitude, electron temperature, and seed duration. An empirical criterion, γ0τc=1, where γ0 is the theoretical growth rate of MRA, is used to choose a proper duration for a higher growth rate. After a total amplification length of 320 μm, the two-beam Raman amplification shows nonlinear features of pulse compression and a bow-shape wave front, indicating that the amplification has finally entered the self-similar regime.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
 Doping effect on the structure and physical properties of quasi-one-dimensional compounds Ba9Co3(Se1-xSx)15 (x = 0-0.2) Lei Duan(段磊), Xian-Cheng Wang(望贤成), Jun Zhang(张俊), Jian-Fa Zhao(赵建发), Wen-Min Li(李文敏), Li-Peng Cao(曹立朋), Zhi-Wei Zhao(赵志伟), Changjiang Xiao(肖长江), Ying Ren(任瑛), Shun Wang(王顺), Jinlong Zhu(朱金龙), and Chang-Qing Jin(靳常青) Chin. Phys. B, 2021, 30 (10):  106101.  DOI: 10.1088/1674-1056/ac1f03 Abstract ( 66 )   HTML ( 0 )   PDF (1668KB) ( 47 )   A series of samples of Ba9Co3(Se1-xSx)15 (x = 0, 0.05, 0.1, 0.15, 0.2) with quasi-one-dimensional (1D) structure were successfully synthesized under high-temperature and high-pressure conditions. The influence of partial substitution of S for Se on the structure, electronic transport, and magnetic properties of Ba9Co3(Se1-xSx)15 has been investigated in detail. The x-ray diffraction data shows that the lattice constant decreases linearly with increasing S-doping level, which follows the Vegrad's law. The doped S atoms preferentially occupy the site of Se atoms in CoSe6 octahedron. Physical properties measurements indicate that all the samples of Ba9Co3(Se1-xSx)15 are semiconducting and display spin glass behavior. As the replacement of Se by smaller size S, although the inter-chain distance decreases, the electronic hopping between CoSe/S6 chains is weakened and leads to an increase of band gap from 0.75 eV to 0.86 eV, since the S-3p electrons are more localized than Se-4p ones. Ba9Co3(Se1-xSx)15 exhibits 1D conducting chain characteristic.
 Spinor F=1 Bose-Einstein condensates loaded in two types of radially-periodic potentials with spin-orbit coupling Ji-Guo Wang(王继国), Yue-Qing Li(李月晴), Han-Zhao Tang(唐翰昭), and Ya-Fei Song(宋亚飞) Chin. Phys. B, 2021, 30 (10):  106701.  DOI: 10.1088/1674-1056/ac1411 Abstract ( 62 )   HTML ( 0 )   PDF (8559KB) ( 34 )   We consider two-dimensional spinor F=1 Bose-Einstein condensates in two types of radially-periodic potentials with spin-orbit coupling, i.e., spin-independent and spin-dependent radially-periodic potentials. For the Bose-Einstein condensates in a spin-independent radially-periodic potential, the density of each component exhibits the periodic density modulation along the azimuthal direction, which realizes the necklacelike state in the ferromagnetic Bose-Einstein condensates. As the spin-exchange interaction increases, the necklacelike state gradually transition to the plane wave phase for the antiferromagnetic Bose-Einstein condensates with larger spin-orbit coupling. The competition of the spin-dependent radially-periodic potential, spin-orbit coupling, and spin-exchange interaction gives rise to the exotic ground-state phases when the Bose-Einstein condensates in a spin-dependent radially-periodic potential.
 Polaron and molecular states of a spin-orbit coupled impurity in a spinless Fermi sea Hong-Hao Yin(尹洪浩), Tian-Yang Xie(谢天扬), An-Chun Ji(纪安春), and Qing Sun(孙青) Chin. Phys. B, 2021, 30 (10):  106702.  DOI: 10.1088/1674-1056/ac1b85 Abstract ( 60 )   HTML ( 0 )   PDF (733KB) ( 42 )   We investigate the polaron and molecular states of a fermionic atom with one-dimensional spin-orbit coupling (SOC) coupled to a three-dimensional spinless Fermi sea. Because of the interplay among the SOC, Raman coupling and spin-selected interatomic interactions, the polaron state induced by the spin-orbit coupled impurity exhibits quite unique features. We find that the energy dispersion of the polaron generally has a double-minimum structure, which results in a finite center-of-mass (c.m.) momentum in the ground state, different from the zero-momentum polarons where SOC are introduced into the majority atoms. By further tuning the parameters such as the atomic interaction strength, a discontinuous transition between the polarons with different c.m. momenta may occur, signaled by the singular behavior of the quasiparticle residue and effective mass of the polaron. Meanwhile, the molecular state as well as the polaron-to-molecule transition is also strongly affected by the Raman coupling and the effective Zeeman field, which are introduced by the lasers generating SOC on the impurity atom. We also discuss the effects of a more general spin-dependent interaction and mass ratio. These results would be beneficial for the study of impurity physics brought by SOC.
 Dielectrowetting actuation of droplet: Theory and experimental validation Yayan Huang(黄亚俨), Rui Zhao(赵瑞), Zhongcheng Liang(梁忠诚), Yue Zhang(张月), Meimei Kong(孔梅梅), and Tao Chen(陈陶) Chin. Phys. B, 2021, 30 (10):  106801.  DOI: 10.1088/1674-1056/ac1926 Abstract ( 39 )   HTML ( 0 )   PDF (943KB) ( 20 )   A theoretical model based on energy conversation is constructed to characterize the contracting behavior of the non-conductive droplet actuated by the dielectric effect in an immiscible dielectric liquid. To verify the theory, COMSOL is employed to simulate the evolution of the droplet based on dielectrowetting, and a measurement platform is established to monitor the change process of the droplet profile. The contact angle and the height of the droplet increase linearly up to 48° and 2.03 mm respectively when U ranges from 55 V to 160 V, while the droplet remained stationary when U < 55 V. The relative experimental results coincide with the prediction of theory and the simulation analysis.
 Direct observation of the scaling relation between density of states and pairing gap in a dirty superconductor Chang-Jiang Zhu(朱长江), Limin Liu(刘立民), Peng-Bo Song(宋鹏博), Han-Bin Deng(邓翰宾), Chang-Jiang Yi(伊长江), Ying-Kai Sun(孙英开), R Wu(武睿), Jia-Xin Yin(殷嘉鑫), Youguo Shi(石友国), Ziqiang Wang(汪自强), and Shuheng H. Pan(潘庶亨) Chin. Phys. B, 2021, 30 (10):  106802.  DOI: 10.1088/1674-1056/ac0903 Abstract ( 62 )   HTML ( 0 )   PDF (3296KB) ( 33 )   Theories and experiments on dirty superconductors are complex but important in terms of both theoretical fundamentals and practical applications. These activities are even more challenging when magnetic fields are present because the field distribution, electron density of states, and superconducting pairing potentials become nonuniform. Here, we present tunneling microspectroscopic experiments on NbC single crystals and demonstrate that NbC is a homogeneous dirty superconductor. When applying magnetic fields to the samples, we found that the zero-energy local density of states and the pairing energy gap followed the explicit scaling relation proposed by de Gennes for homogeneous dirty superconductors in high magnetic fields. More significantly, our experimental findings indicate that the validity of the scaling relation extends to magnetic field strengths far below the upper critical field, calling for a new nonperturbative understanding of this fundamental property in dirty superconductors. On the practical side, we used the observed scaling relation to derive a simple and straightforward experimental scheme for estimating the superconducting coherence length of a dirty superconductor in magnetic fields.
 Scalable fabrication of Bi2O2Se polycrystalline thin film for near-infrared optoelectronic devices applications Bin Liu(刘斌) and Hong Zhou(周洪) Chin. Phys. B, 2021, 30 (10):  106803.  DOI: 10.1088/1674-1056/ac1571 Abstract ( 53 )   HTML ( 0 )   PDF (2173KB) ( 26 )   We present a controlled, stepwise formation of layered semiconductor Bi2O2Se thin films prepared via the vapour process by annealing topological insulator Bi2Se3 thin films in low oxygen atmosphere for different reactions. Photodetectors based on Bi2O2Se thin film show a responsivity of 1.7×104 A/W at a wavelength of 980 nm. Field-effect transistors based on Bi2O2Se thin film exhibit n-type behavior and present a high electron mobility of 17 cm2/V·s. In addition, the electrical properties of the devices after 4 months keeping in the air shows little change, implying outstanding air-stability of our Bi2O2Se thin films. From the obtained results, it is evident that low oxygen annealing is a surprisingly effective method to fabricate Bi2O2Se thin films for integrated optoelectronic applications.
 Molecular simulation study of the adhesion work for water droplets on water monolayer at room temperature Mengyang Qu(屈孟杨), Bo Zhou(周波), and Chunlei Wang(王春雷) Chin. Phys. B, 2021, 30 (10):  106804.  DOI: 10.1088/1674-1056/ac192d Abstract ( 48 )   HTML ( 0 )   PDF (2339KB) ( 40 )   The wetting phenomenon of water droplets coexisting with the ordered water monolayer termed an unexpected phenomenon of “water that does not wet a water monolayer” at room temperature has been found on several solid surfaces. Although the hydrogen bond saturation inside the monolayer can qualitatively describe this phenomenon, whether the Young-Dupré equation still holds under this unconventional wetting framework is still not answered. In this work, we have calculated the contact angle values of the droplets as well as the work of adhesion between the droplets and the monolayer based on an extended phantom-wall method. The results show that similar to the conventional solid-liquid interface, classical Young-Dupré equation is also applicable for the interface of liquid water and ordered water monolayer.
 Temperature effects of GaAs/Al0.45Ga0.55As superlattices on chaotic oscillation Xiao-Peng Luo(罗晓朋), Yan-Fei Liu(刘延飞), Dong-Dong Yang(杨东东), Cheng Chen(陈诚), Xiu-Jian Li(李修建), and Jie-Pan Ying(应杰攀) Chin. Phys. B, 2021, 30 (10):  106805.  DOI: 10.1088/1674-1056/ac04a6 Abstract ( 64 )   HTML ( 0 )   PDF (1081KB) ( 15 )   For widespectrum chaotic oscillation, superlattice cryptography is an autonomous controllable brand-new technology. Originating from sequential resonance tunneling of electrons, the chaotic oscillation is susceptible to temperature change, which determines the performance of superlattices. In this paper, the temperature effects of chaotic oscillations are investigated by analyzing the randomness of a sequence at different temperatures and explained with superlattice microstates. The results show that the bias voltage at different temperatures makes spontaneous chaotic oscillations vary. With the temperature of superlattices changing, the sequence dives in entropy value and randomness at specific bias. This work fills the gap in the study of temperature stability and promotes superlattice cryptography for practice.
 Oxidation degree dependent adsorption of ssDNA onto graphene-based surface Huishu Ma(马慧姝), Jige Chen(陈济舸), Haiping Fang(方海平), and Xiaoling Lei(雷晓玲) Chin. Phys. B, 2021, 30 (10):  106806.  DOI: 10.1088/1674-1056/abf109 Abstract ( 44 )   HTML ( 0 )   PDF (7633KB) ( 13 )   DNA/GO composite plays a significant role in the research field of biotechnology and nanotechnology, and attracts a great deal of interest. However, it is still unclear how the oxidation degree of the graphene-based surface affects the adsorption process of single-strand DNA (ssDNA). In this paper, based on the molecular dynamics simulations, we find that ssDNA molecule is absorbed on the GO surface in the most stable state with the oxidation degree around 15%. The microscopic mechanism is attributed to the van Der Walls and the electrostatic interactions between the ssDNA molecule and the graphene-based surface, which is accompanied with the π-π stacking and hydrogen bond formation. The number of π-π stacking between ssDNA and GO reaches the maximum value when the oxidation degree is around 15% among all the GO surfaces. Our simulation results also reveal the coexistence of stretched and curved configurations as well as the adsorption orientation of ssDNA on the GO surface. Furthermore, it is found that the absorbed ssDNA molecules are more likely to move on the graphene-based surface of low oxidation degree, especially on pristine graphene. Our work provides the physics picture of ssDNA's physisorption dynamics onto graphene-based surface and it is helpful in designing DNA/GO nanomaterials.
 Band engineering of honeycomb monolayer CuSe via atomic modification Lei Gao(高蕾), Yan-Fang Zhang(张艳芳), Jia-Tao Sun(孙家涛), and Shixuan Du(杜世萱) Chin. Phys. B, 2021, 30 (10):  106807.  DOI: 10.1088/1674-1056/abee6f Abstract ( 51 )   HTML ( 0 )   PDF (1366KB) ( 25 )   Two-dimensional monolayer copper selenide (CuSe) has been epitaxially grown and predicted to host the Dirac nodal line fermion (DNLF). However, the metallic state of monolayer CuSe inhibits the potential application of nanoelectronic devices in which a band gap is needed to realize on/off properties. Here, we engineer the band structure of monolayer CuSe which is an analogue of a p-doped system via external atomic modification in an effort to realize the semiconducting state. We find that the H and Li modified monolayer CuSe shifts the energy band and opens an energy gap around the Fermi level. Interestingly, both the atomic and electronic structures of monolayer CuHSe and CuLiSe are very different. The H atoms bind on top of Se atoms of monolayer CuSe with Se-H polar covalent bonds, annihilating the DNLF band of monolayer CuSe dominated by Se orbitals. In contrast, Li atoms prefer to adsorb at the hexagonal center of CuSe, preserving the DNLF band of monolayer CuSe dominated by Se orbitals, but opening band gaps due to a slight buckling of the CuSe layer. The realization of metal-to-semiconductor transition from monolayer CuSe to CuXSe (X=H, Li) as revealed by first-principles calculations makes it possible to use CuSe in future electronic devices.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
 Influence of thickness on current-induced magnetization switching in L10-FePt single layer Shi-Qi Zheng(郑诗琪), Kang-Kang Meng(孟康康), Zhen-Guo Fu(付振国), Ji-Kun Chen(陈吉堃), Jun Miao(苗君), Xiao-Guang Xu(徐晓光), and Yong Jiang(姜勇) Chin. Phys. B, 2021, 30 (10):  107101.  DOI: 10.1088/1674-1056/ac0a62 Abstract ( 43 )   HTML ( 0 )   PDF (1703KB) ( 14 )   The thickness dependent spin-orbit torque (SOT) in an L10-FePt single layer is investigated in this work. As the thickness increases from 8 nm to 16 nm, the magnetization switching ratio in the L10-FePt film with higher chemical ordering becomes smaller. It is noted that compared with 3-nm-thick L10-FePt film, 8-nm-thick L10-FePt film can switch much magnetization with the increase of chemical ordering. When the FePt film is thick enough, the SOT in FePt is closely related to the L10-ordered structure, which indicates a bulk nature. Therefore, the disordering plays an important role in the magnetization switching only for the ultra-thin FePt films, while the structural gradient may play an important role for thicker films. However, both of the two mechanisms cannot fully explain the process of magnetization switching and the spin current generation. Although many factors influence SOT, here in this work we emphasize only the bulk nature of strong SOC in L10-FePt through density functional theory calculations, which should generate large spin current due to spin Hall effect.
 Understanding of impact of carbon doping on background carrier conduction in GaN Zhenxing Liu(刘振兴), Liuan Li(李柳暗), Jinwei Zhang(张津玮), Qianshu Wu(吴千树), Yapeng Wang(王亚朋), Qiuling Qiu(丘秋凌), Zhisheng Wu(吴志盛), and Yang Liu(刘扬) Chin. Phys. B, 2021, 30 (10):  107201.  DOI: 10.1088/1674-1056/abfa0d Abstract ( 39 )   HTML ( 0 )   PDF (2073KB) ( 31 )   The impact of carbon doping on the background carrier conduction in GaN has been investigated. It is found that the incorporation of carbon can effectively suppress the n-type background carrier concentration as expected. Moreover, from the fitting of the temperature-dependent carrier concentration and mobility, it is observed that high nitrogen-vacancy (VN) dominates the background carrier at room temperature which consequently results in n-type conduction. The doping agent (carbon atom) occupies the nitrogen site of GaN and forms CN deep acceptor as revealed from photoluminescence. Besides, a relatively low hole concentration is ionized at room temperature which was insufficient for the compensation of n-type background carriers. Therefore, we concluded that this background carrier concentration can be suppressed by carbon doping, which substitutes the N site of GaN and finally decreases the VN.
 Edge states enhanced by long-range hopping: An analytical study Huiping Wang(王会平), Li Ren(任莉), Liguo Qin(秦立国), and Yueyin Qiu(邱岳寅) Chin. Phys. B, 2021, 30 (10):  107301.  DOI: 10.1088/1674-1056/abe9a5 Abstract ( 43 )   HTML ( 0 )   PDF (1769KB) ( 15 )   We analyze the behavior of edge states in long-range (LR) interacting systems. In terms of lattice model Hamiltonian with the LR coupling, we determine analytically the condition of existence of edge states within the transfer matrix method (TMM). The expressions we obtain are general and hold for any choice of the LR hopping. The reason why edge states can appear is the transfer matrix in the bulk different from that in the boundary layers. Our predictions are in good agreement with numerical results by exact diagonalization. Our result is helpful in solving novel edge states in one- and two-dimensional (2D) superconductors with LR hopping and pairing.
 Goos-Hänchen-like shift related to spin and valley polarization in ferromagnetic silicene Mei-Rong Liu(刘美荣), Zheng-Fang Liu(刘正方), Ruo-Long Zhang(张若龙), Xian-Bo Xiao(肖贤波), and Qing-Ping Wu(伍清萍) Chin. Phys. B, 2021, 30 (10):  107302.  DOI: 10.1088/1674-1056/ac1e16 Abstract ( 32 )   HTML ( 0 )   PDF (1395KB) ( 9 )   We study the Goos-Hänchen-like shift of single silicene barrier under the external perpendicular electric field, off-resonant circularly polarized light and the exchange field modulation using the stationary-phase method. The results show that the Goos-Hänchen-like shift of silicene resulting from the external perpendicular electric field does not have the characteristics of spin or valley polarization, while that from off-resonant circularly polarized light or the exchange field is spin-polarized. More importantly, the combined effect of the external perpendicular electric field and the exchange field or off-resonant circularly polarized light can cause the Goos-Hänchen-like shift of the system to be spin and valley polarized. It is particularly worth noting that when the three modulations are considered at the same time, as the exchange field changes, the system will have a positive or negative Goos-Hänchen-like shift.
 Electrically-manipulable electron-momentum filter based on antiparallel asymmetric double δ-magnetic-barrier semiconductor microstructure Ge Tang (唐鸽), Ying-Jie Qin(覃英杰), Shi-Shi Xie(谢诗诗), and Meng-Hao Sun(孙梦豪) Chin. Phys. B, 2021, 30 (10):  107303.  DOI: 10.1088/1674-1056/ac1570 Abstract ( 23 )   HTML ( 0 )   PDF (619KB) ( 6 )   We theoretically investigate the wave-vector filtering (WVF) effect for electrons in an antiparallel asymmetric double δ-magnetic-barrier microstructure under a bias, which can be fabricated experimentally by patterning two asymmetric ferromagnetic (FM) stripes on the top and the bottom of GaAs/AlxGa1-xAs heterostructure, respectively. It is found that an appreciable WVF effect appears because of an essentially two-dimensional (2D) process for electrons across this microstructure. WVF effect is found to be sensitive to the applied bias. WVF efficiency can be tuned by changing bias, which may lead to an electrically-controllable momentum filter for nanoelectronics device applications.
 Electronic and magnetic properties of single-layer and double-layer VX2 (X=Cl, Br) under biaxial stress Xing Li(李兴), Yanfeng Ge(盖彦峰), Jun Li(李军), Wenhui Wan(万文辉), and Yong Liu(刘永) Chin. Phys. B, 2021, 30 (10):  107305.  DOI: 10.1088/1674-1056/ac0906 Abstract ( 35 )   HTML ( 0 )   PDF (1905KB) ( 21 )   First-principles calculations and Monte Carlo simulations reveal that single-layer and double-layer VX2 (X=Cl, Br) can be tuned from antiferromagnetic (AFM) semiconductors to ferromagnetic (FM) state when biaxial tensile stress is applied. Their ground states are all T phase. The biaxial tensile stress at the phase transition point of the double-layer VX2 is larger than that of the single-layer VX2. The direct band gaps can be also manipulated by biaxial tensile stress as they increases with increasing tensile stress to a critical point and then decreases. The Néel temperature (TN) of double-layer VX2 are higher than that of single-layer. As the stress increases, the TN of all materials tend to increase. The magnetic moment increases with the increase of biaxial tensile stress, and which become insensitive to stress after the phase transition points. Our research provides a method to control the electronic and magnetic properties of VX2 by stress, and the single-layer and double-layer VX2 may have potential applications in nano spintronic devices.
 Effects of electron correlation on superconductivity in the Hatsugai-Kohmoto model Huai-Shuang Zhu(祝怀霜) and Qiang Han(韩强) Chin. Phys. B, 2021, 30 (10):  107401.  DOI: 10.1088/1674-1056/abec36 Abstract ( 43 )   HTML ( 0 )   PDF (552KB) ( 13 )   Understanding how electrons form pairs in the presence of strong electron correlations demands going beyond the BCS paradigm. We study a correlated superconducting model where the correlation effects are accounted for by a U term local in momentum space. The electron correlation is treated exactly while the electron pairing is treated approximately using the mean-field theory. The self-consistent equation for the pair potential is derived and solved. Somewhat contrary to expectation, a weak attractive U comparable to the pair potential can destroy the superconductivity, whereas for weak to intermediate repulsive U, the pair potential can be enhanced. The fidelity of the mean-field ground state is calculated to describe the strength of the elelectron correlation. We show that the pair potential is not equal to the single-electron superconducting gap for the strongly correlated superconductors, in contrast to the uncorrelated BCS limit.
 Superconductivity at 44.4 K achieved by intercalating EMIM+ into FeSe Jinhua Wang(王晋花), Qing Li(李庆), Wei Xie(谢威), Guanyu Chen(陈冠宇), Xiyu Zhu(祝熙宇), and Hai-Hu Wen(闻海虎) Chin. Phys. B, 2021, 30 (10):  107402.  DOI: 10.1088/1674-1056/ac1f09 Abstract ( 78 )   HTML ( 1 )   PDF (2326KB) ( 38 )   Superconductivity with transition temperature Tc above 40 K was observed in protonated FeSe (Hy-FeSe) previously with the ionic liquid EMIM-BF4 used in the electrochemical process. However, the real superconducting phase is not clear until now. And detailed structural, magnetization, and electrical transport measurements are lacking. By using similar protonating technique on FeSe single crystals, we obtain superconducting samples with Tc above 40 K. We show that the obtained superconducting phase is not Hy-FeSe but actually an organic-ion (C6H11N2+ referred to as EMIM+)-intercalated phase (EMIM)xFeSe. By using x-ray diffraction technique, two sets of index peaks corresponding to different c-axis lattice constants are detected in the obtained samples, which belong to the newly formed phase of intercalated (EMIM)xFeSe and the residual FeSe, respectively. The superconductivity of (EMIM)xFeSe with Tc of 44.4 K is confirmed by resistivity and magnetic susceptibility measurements. Temperature dependence of resistivity with different applied magnetic fields reveals that the upper critical field Hc2 is quite high, while the irreversibility field Hirr is suppressed quickly with increasing temperature till about 20 K. This indicates that the resultant compound has a high anisotropy with a large spacing between the FeSe layers.
 Influence of temperature on thermal relaxation of exchange bias field in CoFe/Cu/CoFe/IrMn spin valve Xian-Jin Qi(祁先进), Ni-Na Yang(杨妮娜), Xiao-Xu Duan(段孝旭), and Xue-Zhu Li(李雪竹) Chin. Phys. B, 2021, 30 (10):  107501.  DOI: 10.1088/1674-1056/abec34 Abstract ( 29 )   HTML ( 0 )   PDF (1420KB) ( 10 )   A multilayered spin valve film with a structure of Ta (5 nm)/Co75Fe25(5 nm)/Cu(2.5 nm)/Co75Fe25(5 nm)/Ir20Mn80 (12 nm)/Ta(8 nm) is prepared by the high-vacuum direct current (DC) magnetron sputtering. The effect of temperature on the spin valve structure and the magnetic properties are studied by x-ray diffraction (XRD), atomic force microscopy (AFM), and vibrating sample magnetometry. The effect of temperature on the exchange bias field thermomagnetic properties of multilayered spin valve is studied by the residence time of samples in a reverse saturation field. The results show that as the temperature increases, the IrMn (111) texture weakens, surface/interface roughness increases, and the exchange bias field decreases. Below 200 ℃, the exchange bias field decreases with the residence time increasing, and at the beginning of the negative saturation field, the exchange bias field Hex decreases first quickly and then slowly gradually. When the temperature is greater than 200 ℃, the exchange bias field is unchanged with the residence time increasing.
 Spin-phonon coupling in van der Waals antiferromagnet VOCl Wen-Jun Wang(王文君), Xi-Tong Xu(许锡童), Jie Shen(沈洁), Zhe Wang(王哲), Shi-Le Zhang(张仕乐), and Zhe Qu(屈哲) Chin. Phys. B, 2021, 30 (10):  107502.  DOI: 10.1088/1674-1056/ac041f Abstract ( 44 )   HTML ( 0 )   PDF (2581KB) ( 11 )   We report magnetization and Raman spectroscopy study on single crystals of VOCl, a van der Waals antiferromagnetic material. Magnetization measurement confirms an antiferromagnetic transition at 79 K and a magnetic easy axis along crystallographic a direction. The temperature-dependent Raman spectrum reveals five peaks at 30 K. Below the Neel temperature TN, the Raman-active modes 247 cm-1 and 404 cm-1 remarkably deviate from the standard Boltzmann function, which is ascribed to the strong magnetoelastic coupling between spins and phonons. We further observe an anomaly in 383 cm-1 mode at around 150 K. This coincides with the broad maximum in VOCl's magnetic susceptibility, suggesting a development of short-ranged magnetic order at this temperature.
 Insights into the regulation mechanism of ring-shaped magnetoelectric energy harvesters via mechanical and magnetic conditions Yang Shi(师阳), Ni Li(李妮), and Yong Yang(杨勇) Chin. Phys. B, 2021, 30 (10):  107503.  DOI: 10.1088/1674-1056/abeee9 Abstract ( 45 )   HTML ( 0 )   PDF (1175KB) ( 29 )   This paper presents a theoretical model for predicting and tuning magnetoelectric (ME) effect of ring-shaped composites, in which stress boundary conditions are empoyed and the multi-field coupling property of giant magnetostrictive materials are taken into account. A linear analytical solutions for the closed- and open-circuit ME voltages are derived simultaneously using mechanical differential equations, interface and boundary conditions, and electrical equations. For nonlinear ME coupling effect, the nonlinear multi-field coupling constitutive equation is reduced to an equivalent form by expanding the strains as a Taylor series in the vicinity of bias magnetic field. Sequentially, the linear model is generalized to a nonlinear one involving the field-dependent material parameters. The results show that setting a stress-free condition is beneficial for reducing resonance frequency while applying clamped conditions on the inner and outer boundaries may improve the maximum output power density. In addition, performing stress conditions on one of the boundaries may enhance ME coupling significantly, without changing the corresponding resonance frequency and optimal resistance. When external stimuli like bias magnetic field and pre-stress are applied to the ring-shaped composites, a novel dual peak phenomenon in the ME voltage curve around resonance frequencies is revealed theoretically, indicating that strong ME coupling may be achieved within a wider bias field region. Eventually, the mutual coordination of the bias field and pre-stress may enhance ME coupling as well as tuning the resonance frequency, and thus is pivotal for tunable control of ME energy harvesters. The proposed model can be applied to design high-performance energy harvesters by manipulating the mechanical conditions and external stimuli.
 Crystal growth and magnetic properties of quantum spin liquid candidate KErTe2 Weiwei Liu(刘维维), Dayu Yan(闫大禹), Zheng Zhang(张政), Jianting Ji(籍建葶), Youguo Shi(石友国), Feng Jin(金峰), and Qingming Zhang(张清明) Chin. Phys. B, 2021, 30 (10):  107504.  DOI: 10.1088/1674-1056/ac1574 Abstract ( 73 )   HTML ( 0 )   PDF (3805KB) ( 37 )   Recently rare-earth chalcogenides have been revealed as a family of quantum spin liquid (QSL) candidates hosting a large number of members. In this paper we report the crystal growth and magnetic measurements of KErTe2, which is the first member of telluride in the family. Compared to its cousins of oxides, sulfides and selenides, KErTe2 retains the high symmetry of R3m and Er3+ ions still sit on a perfect triangular lattice. The separation between adjacent magnetic layers is expectedly increased, which further enhances the two dimensionality of the spin system. Specific heat and magnetic susceptibility measurements on KErTe2 single crystals reveal no structural and magnetic transition down to 1.8 K. Most interestingly, the absorption spectrum shows that the charge gap of KErTe2 is roughly 0.93±0.35 eV, which is the smallest among all the reported members in the family. This immediately invokes the interest towards metallization even superconductivity using the compound.
 Magnetic excitations of diagonally coupled checkerboards Tingting Yan(颜婷婷), Shangjian Jin(金尚健), Zijian Xiong(熊梓健), Jun Li(李军), and Dao-Xin Yao(姚道新) Chin. Phys. B, 2021, 30 (10):  107505.  DOI: 10.1088/1674-1056/ac1b94 Abstract ( 50 )   HTML ( 0 )   PDF (1934KB) ( 19 )   By using quantum Monte Carlo based stochastic analytic continuation (QMC-SAC) and spin wave theory, we study magnetic excitations of Heisenberg models with diagonally coupled checkerboard structures. We consider three kinds of checkerboard models (DC 2×2, DC 3×3, and CDC 3×3) consisting nearest-neighbor strong J1 and weak J2 antiferromagnetic interactions. When the coupling ratio g=J2/J1 approaches 1, all three diagonal checkerboards have the same long-range antiferromagnetic Néel order at T=0. When g decreases, the quantum fluctuation can drive DC 2×2 model to quantum paramagnetic state, while DC 3×3 and CDC 3×3 models still have the long-range Néel order. By calculating the magnetic excitations at different coupling ratios, we find that the low-energy part of magnetic excitations calculated by QMC-SAC can be well explained by the spin wave theory. However, the high-energy parts even deep in the long-range antiferromagnetic phase are beyond the spin wave description. Compared to the g=1 uniform square lattice, the high-energy excitations are more rich in our models. Our study may also draw the attention to the high-energy exctitaions beyond the spin wave theory.
 Interaction region of magnon-mediated spin torques and novel magnetic states Zai-Dong Li(李再东), Qi-Qi Guo(郭奇奇), Yong Guo(郭永), Peng-Bin He(贺鹏斌), and Wu-Ming Liu(刘伍明) Chin. Phys. B, 2021, 30 (10):  107506.  DOI: 10.1088/1674-1056/ac04a8 Abstract ( 30 )   HTML ( 0 )   PDF (756KB) ( 10 )   We determine the region in which the magnon-mediated spin torques exist. This region can be controlled by the spin waves. In terms of stability analysis of magnetization dynamics based on the spin-wave background, we obtain the instability conditions of spin waves. With these results, we find the relationship between unstable regions and the formation of Akhmediev breather, Kuznetsov-Ma breather and rogue waves. We establish the phase diagram of some novel magnetic excitaions.
 Effects of Ni substitution on multiferroic properties in Bi5FeTi3O15 ceramics Hui Sun(孙慧), Jiaying Niu(钮佳颖), Haiying Cheng(成海英), Yuxi Lu(卢玉溪), Zirou Xu(徐紫柔), Lei Zhang(张磊), and Xiaobing Chen(陈小兵) Chin. Phys. B, 2021, 30 (10):  107701.  DOI: 10.1088/1674-1056/ac1b92 Abstract ( 48 )   HTML ( 0 )   PDF (3143KB) ( 29 )   The single-phase multiferroic Bi5Fe1-xNixTi3O15 (BFNT-x, x=0, 0.1, 0.2, 0.3, 0.4, and 0.5) ceramics were synthesized by a sol-gel auto-combustion method, and their microstructures, ferroelectric, magnetic, and dielectric properties were investigated in detail. All samples belong to layer-perovskited Aurivillius phase containing four perovskite units sandwiched between two Bi-O layers. Ni substitution can not only improve ferroelectricity but also enhance the magnetic properties. The BFNT-0.2 sample shows the largest remnant polarization (2Pr ～ 11.6 μC/cm2) and the highest remnant magnetization (2Mr ～ 0.244 emu/g). The enhancement of the magnetic properties may mainly originate from the spin canting of Fe/Ni-O octahedra via Dzyaloshinskii-Moriya (DM) interaction. In order to explore the influence of valance state of magnetic ions on the properties, the x-ray photoelectron spectroscopy was carried out. Furthermore, structural, ferroelectric, and magnetic transitions were also investigated.
 Effect of external electric field on crystalline structure anddielectric properties of Bi1.5MgNb1.5O7 thin films Zhongzhe Liu(刘钟喆), Libin Gao(高莉彬), Kexin Liang(梁可欣), Zhen Fang(方针), Hongwei Chen(陈宏伟), and Jihua Zhang(张继华) Chin. Phys. B, 2021, 30 (10):  107703.  DOI: 10.1088/1674-1056/ac0a6b Abstract ( 29 )   HTML ( 0 )   PDF (1544KB) ( 5 )   Bismuth-based cubic pyrochlore materials have attractive dielectric properties, especially dielectric tunability. The Bi1.5MgNb1.5O7 ceramic samples were prepared by solid state reaction. The XRD results and SEM pictures prove the raw material are well mixed and co-fired and the BMN cubic pyrochlore is well crystallized, no second phase was found in the result. BMN thin film were fabricated by depositing BMN ceramic nanoparticles on the sapphire. The BMN thin film has a high dielectric tunability of 43% at a bias voltage of 1.5 MV/cm, with loss tangent lower than 0.009. A Raman study of BMN cubic pyrochlore reveals O'-A-O' and O-A-O bending modes contribute to 80% of dielectric permittivity, obstructing these modes such as applying external electric field can have apparent influence on dielectric constant. Berry Phase calculation results shows that A2O' tetrahedrons are more easy to distort under an external field. The A-site Mg have the highest displacement (0.765028 Å), followed by A-site Bi cations (0.346317 Å). Compared to zero-bias thin film, the biased one with A-O and A-O' bonds being stretched and external coulomb force applied on cations and anions, the dielectric constant under bias field dramatically decreased.
 Conductance and dielectric properties of hydrogen and hydroxyl passivated SiCNWs Wan-Duo Ma(马婉铎), Ya-Lin Li(李亚林), Pei Gong(龚裴), Ya-Hui Jia(贾亚辉), and Xiao-Yong Fang(房晓勇) Chin. Phys. B, 2021, 30 (10):  107801.  DOI: 10.1088/1674-1056/abf130 Abstract ( 31 )   HTML ( 0 )   PDF (1489KB) ( 6 )   Based on the transport theory and the polarization relaxation model, the effects of hydrogen and hydroxyl passivation on the conductivity and dielectric properties of silicon carbide nanowires (SiCNWs) with different sizes are numerically simulated. The results show that the variation trend of conductivity and band gap of passivated SiCNWs are opposite to the scenario of the size effect of bare SiCNWs. Among the influencing factors of conductivity, the carrier concentration plays a leading role. In the dielectric properties, the bare SiCNWs have a strong dielectric response in the blue light region, while passivated SiCNWs show a more obvious dielectric response in the far ultraviolet-light region. In particular, hydroxyl passivation produces a strong dielectric relaxation in the microwave band, indicating that hydroxyl passivated SiCNWs have a wide range of applications in electromagnetic absorption and shielding.
 Optically tuned dielectric characteristics of SrTiO3/Si thin film in the terahertz range Bin Zou(邹斌), Qing-Qing Li(李晴晴), Yu-Ping Yang(杨玉平), and Hai-Zhong Guo(郭海中) Chin. Phys. B, 2021, 30 (10):  107802.  DOI: 10.1088/1674-1056/ac04a7 Abstract ( 61 )   HTML ( 0 )   PDF (764KB) ( 17 )   Active control of the optical parameters in strontium titanate (SrTiO3, STO) thin films is highly desirable for tunable terahertz (THz) integrated devices such as filters, phase modulators, and electro-optical devices. In this work, optically tuned dielectric parameters of a STO thin film epitaxially grown on a silicon wafer were characterized in the THz region with an 800 nm laser pump-THz detection system. The refractive index, extinction coefficient, and complex dielectric constant of the STO thin film were calculated using thin-film parameter extraction. Owing to carrier transportation and soft-mode oscillation, the above optical parameters changed notably with the pump power of the external laser. This study is of great significance for rapid and non-contact THz phase-modulation technology and may serve as a powerful tool to tune the dielectric properties of the STO thin films.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
 Crystal growth, spectral properties and Judd-Ofelt analysis of Pr: CaF2-YF3 Jie Tian(田杰), Xiao Cao(曹笑), Wudi Wang(王无敌), Jian Liu(刘坚), Jianshu Dong(董建树), Donghua Hu(胡冬华), Qingguo Wang(王庆国), Yanyan Xue(薛艳艳), Xiaodong Xu(徐晓东), and Jun Xu(徐军) Chin. Phys. B, 2021, 30 (10):  108101.  DOI: 10.1088/1674-1056/abf921 Abstract ( 31 )   HTML ( 0 )   PDF (1192KB) ( 3 )   The 0.6 at.% Pr3+-doped CaF2-YF3 crystal was successfully grown by the temperature gradient technique (TGT). X-ray diffraction analysis showed that the grown crystal still had cubic structure. The absorption spectrum, emission spectrum, Judd-Ofelt analysis and fluorescence decay curve at room temperature were discussed. The fluorescence lifetime of Pr: CaF2-YF3 crystal was 45.46 μs, and the σem·τ of 3P0→3H6 and 3P0→3F2 transitions were calculated to be 80.92×10-20 cm2·μs and 388.7×10-20 cm2·μs, respectively. The FWHMs are 20.1 nm and 6.8 nm, which are higher than those of Pr: LiYF4, Pr: LiLuF4, Pr: LiGdF4 and Pr: BaY2F8 crystals. The results show that the Pr: CaF2-YF3 crystal is expected to achieve 605 nm orange light and 642 nm red light laser operation.
 Stability and optoelectronic property of lead-free halide double perovskite Cs2B'BiI6 (B' = Li, Na and K) Yunhui Liu(刘云辉), Wei Wang(王威), Feng Xiao(肖峰), Liangbin Xiong(熊良斌), and Xing Ming(明星) Chin. Phys. B, 2021, 30 (10):  108102.  DOI: 10.1088/1674-1056/ac05a5 Abstract ( 41 )   HTML ( 0 )   PDF (1213KB) ( 20 )   Although lead-based perovskite solar cells have achieved more than 25% power conversion efficiency, the toxicity of lead and instability are still urgent problems faced in industrial application. Lead-free halide double perovskite (DP) materials are promising candidates to resolve these issues. Based on the density functional theory, we explore the geometric stability, thermodynamic stability, mechanical stability, electronic structures, and optical properties of the Cs2B'BiI6 (B' =m Li, Na and K) DP materials. By analyzing the tolerance factor and octahedral factor, we find the geometric stabilities of Cs2NaBiI6 and Cs2KBiI6 DPs are better than Cs2LiBiI6. By calculating the total energy, formation energy and decomposition energy, we propose that the most favorable structure of Cs2B'BiI6 is the orthorhombic phase, and Cs2LiBiI6 is less stable relative to the other two counterparts from an energetic viewpoint. Mechanical stability evaluations reveal that the orthorhombic Cs2LiBiI6 material is less stable relative to the isostructural Cs2NaBiI6 and Cs2KBiI6 DPs. The mechanical property calculations indicate that the Cs2B'BiI6 DPs possess good ductility, which can be used as flexible materials. Electronic structures and optical property calculations show that the orthorhombic Cs2B'BiI6 DPs have suitable band gap values, weaker exciton binding energies, and excellent optical absorption performance in the visible-light range. Based on the above comprehensive assessments, we can conclude that the orthorhombic Cs2NaBiI6 and Cs2KBiI6 DPs with good stability are promising candidates for solar cell applications.
 Heating rate effects for the melting transition of Pt-Ag-Au nanoalloys Hüseyin Yıldırım and Ali Kemal Garip Chin. Phys. B, 2021, 30 (10):  108201.  DOI: 10.1088/1674-1056/abee09 Abstract ( 42 )   HTML ( 0 )   PDF (1423KB) ( 10 )   The classical molecular dynamics simulations in canonical NVT ensemble conditions are used to investigate the melting transition in different heating rates of Pt-Ag-Au ternary nanoalloys. In order to obtain the initial configurations used in the molecular dynamics simulations, optimizing the chemical ordering of Pt13AgnAu42-n (n=0-42) ternary nanoalloys was performed using the Basin-Hopping algorithm which would not allow changes in the icosahedron structure. The Gupta many-body potential was used to model interatomic interactions in both molecular dynamics simulations and optimization simulations. The melting transitions of selected Pt-Ag-Au nanoalloys were explored using caloric curves and Lindemann parameters. There have been two identified types of melting mechanisms, one includes sudden jump behavior in the caloric curve and the other is an isomerization while melting transition. The temperature range in which the isomerization takes place depends on the heating rate value.
 Driven injection of a polymer into a spherical cavity: A Langevin dynamics simulation study Chao Wang(王超), Fan Wu(吴凡), Xiao Yang(杨肖), Ying-Cai Chen(陈英才), and Meng-Bo Luo(罗孟波) Chin. Phys. B, 2021, 30 (10):  108202.  DOI: 10.1088/1674-1056/abff21 Abstract ( 27 )   HTML ( 0 )   PDF (602KB) ( 6 )   The injection of a self-avoiding flexible polymer into a spherical cavity under a driving force is studied by using Langevin dynamics simulation. For given polymer length (N) and driving force (f), the polymer can be completely injected into the cavity only when the radius of the cavity is larger than a transition radius (ReC). The dependence of ReC on N and f can be described by a scaling relation ReC∝N1/3f-δ. The value of δ changes from 4/15 in the small f region to 1/6 in the moderate f region due to the screening of the excluded-volume interaction between monomers. We find the complete injection time (τ) decreases monotonously with increasing the cavity radius or decreasing the polymer length. The simulation results are in good agreement with the theoretical predictions from the free energy analysis and a simple kinetic model.
 Single-molecule mechanical folding and unfolding kinetics of armless mitochondrial tRNAArg from Romanomermis culicivorax Yan-Hui Li(李彦慧), Zhen-Sheng Zhong(钟振声), and Jie Ma(马杰) Chin. Phys. B, 2021, 30 (10):  108203.  DOI: 10.1088/1674-1056/ac1e1e Abstract ( 56 )   HTML ( 0 )   PDF (1059KB) ( 37 )   The mechanical stability of tRNAs contributes to their biological activities. The mitochondrial tRNAArg from Romanomermis culicivorax is the shortest tRNA ever known. This tRNA lacks D- and T-arms, represents a stem-bulge-stem architecture but still folds into a stable tertiary structure. Although its structure had been reported, studies on its mechanical folding and unfolding kinetic characteristics are lacking. Here, we directly measured the single-molecule mechanical folding and unfolding kinetics of the armless mt tRNAArg by using optical tweezers in different solution conditions. We revealed a two-step reversible unfolding pathway: the first and large transition corresponds to the unfolding of acceptor stem and bulge below 11 pN, and the second and small transition corresponds to the unfolding of anticodon arm at 12 pN-14 pN. Moreover, the free energy landscapes of the unfolding pathways were reconstructed. We also demonstrated that amino acid-chelated Mg2+(aaCM), which mimics the intracellular solution condition, stabilizes the bulge of mitochondrial tRNAArg possibly by reducing the topological constraints or stabilizing the possible local non-canonical base pairings within the bulge region. Our study revealed the solution-dependent mechanical stability of an armless mt tRNA, which may shed light on future mt tRNA studies.
 Impact of oxygen in electrical properties and hot-carrier stress-induced degradation of GaN high electron mobility transistors Lixiang Chen(陈丽香), Min Ma(马敏), Jiecheng Cao(曹杰程), Jiawei Sun(孙佳惟), Miaoling Que(阙妙玲), and Yunfei Sun(孙云飞) Chin. Phys. B, 2021, 30 (10):  108502.  DOI: 10.1088/1674-1056/ac1efd Abstract ( 44 )   HTML ( 0 )   PDF (2657KB) ( 28 )   The role of the oxygen in AlGaN/GaN high electron mobility transistors (HEMTs) before and after semi-on state stress was discussed. Comparing with the electrical characteristics of the devices in vacuum, air, and oxygen atmosphere, it is revealed that the oxygen has significant influence on the electric characteristics and the hot-carrier-stress-induced degradation of the device. Comparing with the situation in vacuum, the gate leakage increased an order of magnitude in oxygen and air atmosphere. Double gate structure was used to separate the barrier leakage and surface leakage of AlGaN/GaN HEMT it is found that surface leakage is the major influencing factor in gate leakage of SiN-passivated devices before and after semi-on state stress. During semi-on state stress in the oxygen atmosphere, the electric-field-driven oxidation process promoted the oxidation of the nitride layer, and the oxidation layer in the SiN/AlGaN interface leads to the decreasing of the surface leakage.
 Identification of key residues in protein functional movements by using molecular dynamics simulations combined with a perturbation-response scanning method Jun-Bao Ma(马君宝), Wei-Bu Wang(王韦卜), and Ji-Guo Su(苏计国) Chin. Phys. B, 2021, 30 (10):  108701.  DOI: 10.1088/1674-1056/abf12f Abstract ( 37 )   HTML ( 0 )   PDF (1738KB) ( 10 )   The realization of protein functional movement is usually accompanied by specific conformational changes, and there exist some key residues that mediate and control the functional motions of proteins in the allosteric process. In the present work, the perturbation-response scanning method developed by our group was combined with the molecular dynamics (MD) simulation to identify the key residues controlling the functional movement of proteins. In our method, a physical quantity that is directly related to protein specific function was introduced, and then based on the MD simulation trajectories, the perturbation-response scanning method was used to identify the key residues for functional motions, in which the residues that highly correlated with the fluctuation of the function-related quantity were identified as the key residues controlling the specific functional motions of the protein. Two protein systems, i.e., the heat shock protein 70 and glutamine binding protein, were selected as case studies to validate the effectiveness of our method. Our calculated results are in good agreement with the experimental results. The location of the key residues in the two proteins are similar, indicating the similar mechanisms behind the performance of their biological functions.
 Holographic heat engine efficiency of hyperbolic charged black holes Wei Sun(孙威) and Xian-Hui Ge(葛先辉) Chin. Phys. B, 2021, 30 (10):  109501.  DOI: 10.1088/1674-1056/ac1e0c Abstract ( 49 )   HTML ( 0 )   PDF (2401KB) ( 35 )   We consider a four-dimensional charged hyperbolic black hole as working matter to establish a black hole holographic heat engine, and use the rectangular cycle to obtain the heat engine efficiency. We find that when the increasing of entropy is zero, the heat engine efficiency of the hyperbolic black hole becomes the well-known Carnot efficiency. We also find that less charge corresponds to higher efficiency in the case of $\tilde{q}>0$. Furthermore, we study the efficiency of the flat case and spherical case and compare the efficiency with that of the hyperbolic charged black holes. Finally, we use numerical simulation to study the efficiency in benchmark scheme.