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    Fractal sorting vector-based least significant bit chaotic permutation for image encryption
    Yong-Jin Xian(咸永锦), Xing-Yuan Wang(王兴元), Ying-Qian Zhang(张盈谦), Xiao-Yu Wang(王晓雨), and Xiao-Hui Du(杜晓慧)
    Chin. Phys. B, 2021, 30 (6): 060508.   DOI: 10.1088/1674-1056/abda35
    Abstract1344)   HTML30)    PDF (10704KB)(1897)      
    The image's least significant bit (LSB) covers lots of the details that have been commonly used in image encryption analysis. The newly proposed fractal sorting vector (FSV) and FSV-based LSB chaotic permutation (FSV-LSBCP) is a novel chaotic image encryption cryptosystem introduced in this article. The FSV-LSBCP effectively strengthens the security of the cryptographic scheme concerning the properties of the FSV. Key analysis, statistical analysis, resistance differential attack analysis, and resistance to cropping attacks and noise attacks are the focus of the suggested image encryption cryptosystem. The security experiment shows that the cryptosystem is adequate to achieve the desired degree of security.
    Calculations of atomic polarizability for beryllium using MCDHF method
    Hui Dong(董辉), Jun Jiang(蒋军), Zhongwen Wu(武中文), Chenzhong Dong(董晨钟), and Gediminas Gaigalas
    Chin. Phys. B, 2021, 30 (4): 043103.   DOI: 10.1088/1674-1056/abd92d
    Abstract309)   HTML0)    PDF (745KB)(1575)      
    Based on the fully relativistic multiconfiguration Dirac-Hartree-Fock (MCDHF) method and the corresponding program package GRASP2018, a new program for calculating the polarizabilities is developed. As the first application, the static electric-dipole polarizabilities of the ground state 2s2 1S0 and excited state 2s2p 3P0 of beryllium are calculated. By means of these polarizabilities, the blackbody radiation (BBR) shift of the 2s2p $^3P_0 \to \rm 2s^2$ 1S0 clock transition is determined. The present results agree very well with other available theoretical results.
    Quantization of the band at the surface of charge density wave material 2H-TaSe2
    Man Li(李满), Nan Xu(徐楠), Jianfeng Zhang(张建丰), Rui Lou(娄睿), Ming Shi(史明), Lijun Li(黎丽君), Hechang Lei(雷和畅), Cedomir Petrovic, Zhonghao Liu(刘中灏), Kai Liu(刘凯), Yaobo Huang(黄耀波), and Shancai Wang(王善才)
    Chin. Phys. B, 2021, 30 (4): 047305.   DOI: 10.1088/1674-1056/abe9a8
    Abstract728)   HTML0)    PDF (1794KB)(734)      
    By using angle-resolved photoemission spectroscopy (ARPES) combined with the first-principles electronic structure calculations, we report the quantized states at the surface of a single crystal 2H-TaSe2. We have observed sub-bands of quantized states at the three-dimensional Brillouin zone center due to a highly dispersive band with light effective mass along kz direction. The quantized sub-bands shift upward towards EF while the bulk band at $\varGamma$ shifts downward with the decrease of temperature across charge density wave (CDW) formation. The band shifts could be intimately related to the CDW. While neither the two-dimensional Fermi-surface nesting nor purely strong electron-phonon coupling can explain the mechanism of CDW in 2H-TaSe2, our experiment may ignite the interest in understanding the CDW mechanism in this family.
    Transport property of inhomogeneous strained graphene
    Bing-Lan Wu(吴冰兰), Qiang Wei(魏强), Zhi-Qiang Zhang(张智强), and Hua Jiang(江华)
    Chin. Phys. B, 2021, 30 (3): 030504.   DOI: 10.1088/1674-1056/abe3e3
    Abstract665)   HTML8)    PDF (1974KB)(669)      
    In analogy to real magnetic field, the pseudo-magnetic field (PMF) induced by inhomogeneous strain can also form the Landau levels and edge states. In this paper, the transport properties of graphene under inhomogeneous strain are studied. We find that the Landau levels have non-zero group velocity, and construct one-dimensional conducting channels. In addition, the edge states and the Landau level states in PMF are both fragile under disorder. We also confirm that the backscattering of these states could be suppressed by applying a real magnetic filed (MF). Therefore, the transmission coefficient for each conducting channel can be manipulated by adjusting the MF strength, which indicates the application of switching devices.
    Search for topological defect of axionlike model with cesium atomic comagnetometer
    Yucheng Yang(杨雨成), Teng Wu(吴腾), Jianwei Zhang(张建玮), and Hong Guo(郭弘)
    Chin. Phys. B, 2021, 30 (5): 050704.   DOI: 10.1088/1674-1056/abf132
    Abstract626)   HTML1)    PDF (916KB)(623)      
    Many terrestrial experiments have been designed to detect domain walls composed of axions or axionlike particles (ALPs), which are promising candidates of dark matter. When the domain wall crosses over the Earth, the pseudoscalar field of ALPs could couple to the atomic spins. Such exotic spin-dependent couplings can be searched for by monitoring the transient-in-time change of the atomic spin precession frequency in the presence of a magnetic field. We propose here a single-species cesium atomic comagnetometer, which measures the spin precession frequencies of atoms in different ground-state hyperfine levels, to eliminate the common-mode magnetic-field variations and search for the exotic non-magnetic couplings solely between protons and ALPs. With the single-species atomic comagnetometer, we experimentally rule out the possibility that the decay constant of the linear pseudoscalar couplings of ALPs to protons is $f_{\rm p}\lesssim 3.71\times 10^{7}~\rm{GeV}$. The advanced system has the potential to constrain the constant to be $f_{\rm p}\lesssim 10.7\times 10^{9}~\rm{GeV}$, promising to improve astrophysical constraint level by at least one order of magnitude. Our system could provide a sensitive detection method for the global network of optical magnetometers to search for exotic physics.
    Numerical analysis of motional mode coupling of sympathetically cooled two-ion crystals
    Li-Jun Du(杜丽军), Yan-Song Meng(蒙艳松), Yu-Ling He(贺玉玲), and Jun Xie(谢军)
    Chin. Phys. B, 2021, 30 (7): 073702.   DOI: 10.1088/1674-1056/abfc3e
    Abstract211)   HTML0)    PDF (1029KB)(622)      
    A two-ion pair in a linear Paul trap is extensively used in the research of the simplest quantum-logic system; however, there are few quantitative and comprehensive studies on the motional mode coupling of two-ion systems yet. This study proposes a method to investigate the motional mode coupling of sympathetically cooled two-ion crystals by quantifying three-dimensional (3D) secular spectra of trapped ions using molecular dynamics simulations. The 3D resonance peaks of the 40Ca+-27Al+ pair obtained by using this method were in good agreement with the 3D in- and out-of-phase modes predicted by the mode coupling theory for two ions in equilibrium and the frequency matching errors were lower than 2%. The obtained and predicted amplitudes of these modes were also qualitatively similar. It was observed that the strength of the sympathetic interaction of the 40Ca+-27Al+ pair was primarily determined by its axial in-phase coupling. In addition, the frequencies and amplitudes of the ion pair's resonance modes (in all dimensions) were sensitive to the relative masses of the ion pair, and a decrease in the mass mismatch enhanced the sympathetic cooling rates. The sympathetic interactions of the 40Ca+-27Al+ pair were slightly weaker than those of the 24Mg+-27Al+ pair, but significantly stronger than those of 9Be+-27Al+. However, the Doppler cooling limit temperature of 40Ca+ is comparable to that of 9Be+ but lower than approximately half of that of 24Mg+. Furthermore, laser cooling systems for 40Ca+ are more reliable than those for 24Mg+ and 9Be+. Therefore, 40Ca+ is probably the best laser-cooled ion for sympathetic cooling and quantum-logic operations of 27Al+ and has particularly more notable comprehensive advantages in the development of high reliability, compact, and transportable 27Al+ optical clocks. This methodology may be extended to multi-ion systems, and it will greatly aid efforts to control the dynamic behaviors of sympathetic cooling as well as the development of low-heating-rate quantum logic clocks.
    Widely tunable single-photon source with high spectral-purity from telecom wavelength to mid-infrared wavelength based on MgO:PPLN
    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
    Abstract658)   HTML2)    PDF (1543KB)(609)      
    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.
    Gate-controlled magnetic transitions in Fe3GeTe2 with lithium ion conducting glass substrate
    Guangyi Chen(陈光毅), Yu Zhang(张玉), Shaomian Qi(齐少勉), and Jian-Hao Chen(陈剑豪)
    Chin. Phys. B, 2021, 30 (9): 097504.   DOI: 10.1088/1674-1056/ac1338
    Abstract512)   HTML1)    PDF (806KB)(508)      
    Since the discovery of magnetism in two dimensions, effective manipulation of magnetism in van der Waals magnets has always been a crucial goal. Ionic gating is a promising method for such manipulation, yet devices gated with conventional ionic liquid may have some restrictions in applications due to the liquid nature of the gate dielectric. Lithium-ion conducting glass-ceramics (LICGC), a solid Li+ electrolyte, could be used as a substrate while simultaneously acts as a promising substitute for ionic liquid. Here we demonstrate that the ferromagnetism of Fe3GeTe2 (FGT) could be modulated via LICGC. By applying a voltage between FGT and the back side of LICGC substrate, Li+ doping occurs and causes the decrease of the coercive field (Hc) and ferromagnetic transition temperature (Tc) in FGT nanoflakes. A modulation efficiency for Hc of up to ~ 24.6% under Vg = 3.5 V at T =100 K is achieved. Our results provide another method to construct electrically-controlled magnetoelectronics, with potential applications in future information technology.
    Measuring Loschmidt echo via Floquet engineering in superconducting circuits
    Shou-Kuan Zhao(赵寿宽), Zi-Yong Ge(葛自勇), Zhong-Cheng Xiang(相忠诚), Guang-Ming Xue(薛光明), Hai-Sheng Yan(严海生), Zi-Ting Wang(王子婷), Zhan Wang(王战), Hui-Kai Xu(徐晖凯), Fei-Fan Su(宿非凡), Zhao-Hua Yang(杨钊华), He Zhang(张贺), Yu-Ran Zhang(张煜然), Xue-Yi Guo(郭学仪), Kai Xu(许凯), Ye Tian(田野), Hai-Feng Yu(于海峰), Dong-Ning Zheng(郑东宁), Heng Fan(范桁), and Shi-Ping Zhao(赵士平)
    Chin. Phys. B, 2022, 31 (3): 030307.   DOI: 10.1088/1674-1056/ac40f8
    Abstract543)   HTML1)    PDF (1107KB)(501)      
    The Loschmidt echo is a useful diagnostic for the perfection of quantum time-reversal process and the sensitivity of quantum evolution to small perturbations. The main challenge for measuring the Loschmidt echo is the time reversal of a quantum evolution. In this work, we demonstrate the measurement of the Loschmidt echo in a superconducting 10-qubit system using Floquet engineering and discuss the imperfection of an initial Bell-state recovery arising from the next-nearest-neighbor (NNN) coupling present in the qubit device. Our results show that the Loschmidt echo is very sensitive to small perturbations during quantum-state evolution, in contrast to the quantities like qubit population that is often considered in the time-reversal experiment. These properties may be employed for the investigation of multiqubit system concerning many-body decoherence and entanglement, etc., especially when devices with reduced or vanishing NNN coupling are used.
    Density functional theory investigation on lattice dynamics, elastic properties and origin of vanished magnetism in Heusler compounds CoMnVZ (Z= Al, Ga)
    Guijiang Li(李贵江), Enke Liu(刘恩克), Guodong Liu(刘国栋), Wenhong Wang(王文洪), and Guangheng Wu(吴光恒)
    Chin. Phys. B, 2021, 30 (8): 083103.   DOI: 10.1088/1674-1056/ac0a6a
    Abstract578)   HTML5)    PDF (1511KB)(485)      
    The lattice dynamics, elastic properties and the origin of vanished magnetism in equiatomic quaternary Heusler compounds CoMnVZ (Z=Al, Ga) are investigated by first principle calculations in this work. Due to the similar constituent atoms in CoMnVAl and CoMnVGa compounds, they are both stable in LiMgPdSn-type structure with comparable lattice size, phonon dispersions and electronic structures. Comparatively, we find that CoMnVAl is more structurally stable than CoMnVGa. Meanwhile, the increased covalent bonding component in CoMnVAl enhances its mechanical strength and Vickers hardness, which leads to better comprehensive mechanical properties than those of CoMnVGa. Practically and importantly, structural and chemical compatibilities at the interface make non-magnetic semiconductor CoMnVAl and magnetic topological semimetals Co2MnAl/Ga more suitable to be grown in heterostructures. Owing to atomic preferential occupation in CoMnVAl/Ga, the localized atoms Mn occupy C (0.5, 0.5, 0.5) Wyckoff site rather than B (0.25, 0.25, 0.25) and D (0.75, 0.75, 0.75) Wyckoff sites in LiMgPdSn-type structure, which results in symmetric band filling and consequently drives them to be non-magnetic. Correspondingly, by tuning localized atoms Mn to occupy B (0.25, 0.25, 0.25) or/and D (0.75, 0.75, 0.75) Wyckoff sites in off-stoichiometric Co-Mn-V-Al/Ga compounds and keeping the total valence electrons as 24, newly compensated ferrimagnetic compounds are theoretically achieved. We hope that our work will provide more choices for spintronic applications.
    Superconductivity in an intermetallic oxide Hf3Pt4Ge2O
    Chengchao Xu(徐程超), Hong Wang(王鸿), Huanfang Tian(田焕芳), Youguo Shi(石友国), Zi-An Li(李子安), Ruijuan Xiao(肖睿娟), Honglong Shi(施洪龙), Huaixin Yang(杨槐馨), and Jianqi Li(李建奇)
    Chin. Phys. B, 2021, 30 (7): 077403.   DOI: 10.1088/1674-1056/abfb53
    Abstract558)   HTML0)    PDF (3238KB)(449)      
    Discovery of a new superconductor with distinct crystal structure and chemistry often provides great opportunity for further expanding superconductor material base, and also leads to better understanding of superconductivity mechanisms. Here, we report the discovery of superconductivity in a new intermetallic oxide Hf3Pt4Ge2O synthesized through a solid-state reaction. The Hf3Pt4Ge2O crystallizes in a cubic structure (space group Fm-3m) with a lattice constant of a = 1.241 nm, whose stoichiometry and atomic structure are determined by electron microscopy and x-ray diffraction techniques. The superconductivity at 4.1 K and type-Ⅱ superconducting nature are evidenced by the electrical resistivity, magnetic susceptibility, and specific heat measurements. The intermetallic oxide Hf3Pt4Ge2O system demonstrates an intriguing structural feature that foreign oxygen atoms can be accommodated in the interstitial sites of the ternary intermetallic framework. We also successfully synthesized a series of Hf3Pt4Ge2O1+δ (-0.25 ≤ δ ≤ 0.5), and found the δ-dependent superconducting transition temperature Tc. The atomic structure and the electronic structure are also substantiated by first-principles calculations. Our results present an entirely new family of superconductors with distinct structural and chemical characteristics, and could attract research interest in further finding new superconductors and exploring novel physics pertaining to the 5d-electron in these intermetallic compound systems.
    A double quantum dot defined by top gates in a single crystalline InSb nanosheet
    Yuanjie Chen(陈元杰), Shaoyun Huang(黄少云), Jingwei Mu(慕经纬), Dong Pan(潘东), Jianhua Zhao(赵建华), and Hong-Qi Xu(徐洪起)
    Chin. Phys. B, 2021, 30 (12): 128501.   DOI: 10.1088/1674-1056/abff2e
    Abstract562)   HTML2)    PDF (1960KB)(423)      
    We report on the transport study of a double quantum dot (DQD) device made from a freestanding, single crystalline InSb nanosheet. The freestanding nanosheet is grown by molecular beam epitaxy and the DQD is defined by the top gate technique. Through the transport measurements, we demonstrate how a single quantum dot (QD) and a DQD can be defined in an InSb nanosheet by tuning voltages applied to the top gates. We also measure the charge stability diagrams of the DQD and show that the charge states and the inter-dot coupling between the two individual QDs in the DQD can be efficiently regulated by the top gates. Numerical simulations for the potential profile and charge density distribution in the DQD have been performed and the results support the experimental findings and provide a better understanding of fabrication and transport characteristics of the DQD in the InSb nanosheet. The achieved DQD in the two-dimensional InSb nanosheet possesses pronounced benefits in lateral scaling and can thus serve as a new building block for the developments of quantum computation and quantum simulation technologies.
    Plasmonic properties of graphene on uniaxially anisotropic substrates
    Shengchuan Wang(汪圣川), Bin You(游斌), Rui Zhang(张锐), Kui Han(韩奎), Xiaopeng Shen(沈晓鹏, and Weihua Wang(王伟华)
    Chin. Phys. B, 2021, 30 (3): 037801.   DOI: 10.1088/1674-1056/abd168
    Abstract333)   HTML4)    PDF (17038KB)(410)      
    Most of the current graphene plasmonic researches are based on the substrates with isotropic dielectric constant such as silicon. In this work, we investigate optical properties of graphene nanoribbon arrays placed on a uniaxially anisotropic substrate, where the anisotropy provides an additional freedom to tune the behaviors of graphene plasmons, and its effect can be described by a simple effective formula. In practice, the substrates of semi-infinite and finite thickness are discussed by using both the formula and full wave simulations. Particularly, the dielectric constants $\varepsilon_ \parallel $ and $\varepsilon_ \bot $ approaching zero are intensively studied, which show different impacts on the transverse magnetic (TM) surface modes. In reality, the hexagonal boron nitride (hBN) can be chosen as the anisotropic substrate, which is also a hyperbolic material in nature.
    Reversible waveform conversion between microwave and optical fields in a hybrid opto-electromechanical system
    Li-Guo Qin(秦立国), Zhong-Yang Wang(王中阳), Jie-Hui Huang(黄接辉), Li-Jun Tian(田立君), and Shang-Qing Gong(龚尚庆)
    Chin. Phys. B, 2021, 30 (6): 068502.   DOI: 10.1088/1674-1056/abea8f
    Abstract490)   HTML0)    PDF (1493KB)(407)      
    We present a scheme of reversible waveform conversion between microwave and optical fields in the hybrid opto-electromechanical system. As an intermediate interface, nanomechanical resonator optomechanically couples both optomechanical cavities in the optical and microwave frequency domains. We find the double-optomechanically induced transparency and achieve coherent signal waveform bi-directional transfer between microwave and optical fields based on quantum interference. In addition, we give an analytical expression of one-to-one correspondence between the microwave field and the optical output field, which intuitively shows the reversible waveform conversion relationship. In particular, by numerical simulations and approximate expression, we demonstrate the conversion effects of the three waveforms and discuss the bi-directional conversion efficiency and the bandwidth. such a hybrid opto- and electro-mechanical device has significant potential functions for electro-optic modulation and waveform conversion of quantum microwave-optical field in optical communications and further quantum networks.
    A composite micromotor driven by self-thermophoresis and Brownian rectification
    Xin Lou(娄辛), Nan Yu(余楠), Ke Chen(陈科), Xin Zhou(周昕), Rudolf Podgornik, and Mingcheng Yang(杨明成)
    Chin. Phys. B, 2021, 30 (11): 114702.   DOI: 10.1088/1674-1056/ac2727
    Abstract474)   HTML1)    PDF (517KB)(404)      
    Brownian motors and self-phoretic microswimmers are two typical micromotors, for which thermal fluctuations play different roles. Brownian motors utilize thermal noise to acquire unidirectional motion, while thermal fluctuations randomize the self-propulsion of self-phoretic microswimmers. Here we perform mesoscale simulations to study a composite micromotor composed of a self-thermophoretic Janus particle under a time-modulated external ratchet potential. The composite motor exhibits a unidirectional transport, whose direction can be reversed by tuning the modulation frequency of the external potential. The maximum transport capability is close to the superposition of the drift speed of the pure Brownian motor and the self-propelling speed of the pure self-thermophoretic particle. Moreover, the hydrodynamic effect influences the orientation of the Janus particle in the ratched potential, hence also the performance of the composite motor. Our work thus provides an enlightening attempt to actively exploit inevitable thermal fluctuations in the implementation of the self-phoretic microswimmers.
    Direct visualization of structural defects in 2D semiconductors
    Yutuo Guo(郭玉拓), Qinqin Wang(王琴琴), Xiaomei Li(李晓梅), Zheng Wei(魏争), Lu Li(李璐), Yalin Peng(彭雅琳), Wei Yang(杨威), Rong Yang(杨蓉), Dongxia Shi(时东霞), Xuedong Bai(白雪冬), Luojun Du(杜罗军), and Guangyu Zhang(张广宇)
    Chin. Phys. B, 2022, 31 (7): 076105.   DOI: 10.1088/1674-1056/ac6738
    Abstract538)   HTML35)    PDF (4731KB)(398)      
    Direct visualization of the structural defects in two-dimensional (2D) semiconductors at a large scale plays a significant role in understanding their electrical/optical/magnetic properties, but is challenging. Although traditional atomic resolution imaging techniques, such as transmission electron microscopy and scanning tunneling microscopy, can directly image the structural defects, they provide only local-scale information and require complex setups. Here, we develop a simple, non-invasive wet etching method to directly visualize the structural defects in 2D semiconductors at a large scale, including both point defects and grain boundaries. Utilizing this method, we extract successfully the defects density in several different types of monolayer molybdenum disulfide samples, providing key insights into the device functions. Furthermore, the etching method we developed is anisotropic and tunable, opening up opportunities to obtain exotic edge states on demand.
    Discontinuous and continuous transitions of collective behaviors in living systems
    Xu Li(李旭), Tingting Xue(薛婷婷), Yu Sun(孙宇), Jingfang Fan(樊京芳), Hui Li(李辉), Maoxin Liu(刘卯鑫), Zhangang Han(韩战钢), Zengru Di(狄增如), and Xiaosong Chen(陈晓松)
    Chin. Phys. B, 2021, 30 (12): 128703.   DOI: 10.1088/1674-1056/ac3c3f
    Abstract512)   HTML6)    PDF (1918KB)(395)      
    Living systems are full of astonishing diversity and complexity of life. Despite differences in the length scales and cognitive abilities of these systems, collective motion of large groups of individuals can emerge. It is of great importance to seek for the fundamental principles of collective motion, such as phase transitions and their natures. Via an eigen microstate approach, we have found a discontinuous transition of density and a continuous transition of velocity in the Vicsek models of collective motion, which are identified by the finite-size scaling form of order-parameter. At strong noise, living systems behave like gas. With the decrease of noise, the interactions between the particles of a living system become stronger and make them come closer. The living system experiences then a discontinuous gas-liquid like transition of density. The even stronger interactions at smaller noise make the velocity directions of the particles become ordered and there is a continuous phase transition of collective motion in addition.
    Solving quantum rotor model with different Monte Carlo techniques
    Weilun Jiang(姜伟伦), Gaopei Pan(潘高培), Yuzhi Liu(刘毓智), and Zi-Yang Meng(孟子杨)
    Chin. Phys. B, 2022, 31 (4): 040504.   DOI: 10.1088/1674-1056/ac4f52
    Abstract522)   HTML4)    PDF (1004KB)(385)      
    We systematically test the performance of several Monte Carlo update schemes for the (2+1)d XY phase transition of quantum rotor model. By comparing the local Metropolis (LM), LM plus over-relaxation (OR), Wolff-cluster (WC), hybrid Monte Carlo (HM), hybrid Monte Carlo with Fourier acceleration (FA) schemes, it is clear that among the five different update schemes, at the quantum critical point, the WC and FA schemes acquire the smallest autocorrelation time and cost the least amount of CPU hours in achieving the same level of relative error, and FA enjoys a further advantage of easily implementable for more complicated interactions such as the long-range ones. These results bestow one with the necessary knowledge of extending the quantum rotor model, which plays the role of ferromagnetic/antiferromagnetic critical bosons or Z2 topological order, to more realistic and yet challenging models such as Fermi surface Yukawa-coupled to quantum rotor models.
    Electronic structures and topological properties of TeSe2 monolayers
    Zhengyang Wan(万正阳), Hao Huan(郇昊), Hairui Bao(鲍海瑞), Xiaojuan Liu(刘晓娟), and Zhongqin Yang(杨中芹)
    Chin. Phys. B, 2021, 30 (11): 117304.   DOI: 10.1088/1674-1056/ac2489
    Abstract511)   HTML4)    PDF (2793KB)(373)      
    The successfully experimental fabrication of two-dimensional Te monolayer films [Phys. Rev. Lett. 119 106101 (2017)] has promoted the researches on the group-VI monolayer materials. In this work, the electronic structures and topological properties of a group-VI binary compound of TeSe2 monolayers are studied based on the density functional theory and Wannier function method. Three types of structures, namely, α-TeSe2, β-TeSe2, and γ-TeSe2, are proposed for the TeSe2 monolayer among which the α-TeSe2 is found being the most stable. All the three structures are semiconductors with indirect band gaps. Very interestingly, the γ-TeSe2 monolayer becomes a quantum spin Hall (QSH) insulator with a global nontrivial energy gap of 0.14 eV when a 3.5% compressive strain is applied. The opening of the global band gap is understood by the competition between the decrease of the local band dispersion and the weakening of the interactions between the Se px, py orbitals and Te px, py orbitals during the process. Our work realizes topological states in the group-VI monolayers and promotes the potential applications of the materials in spintronics and quantum computations.
    Gauss quadrature based finite temperature Lanczos method
    Jian Li(李健) and Hai-Qing Lin(林海青)
    Chin. Phys. B, 2022, 31 (5): 050203.   DOI: 10.1088/1674-1056/ac5986
    Abstract399)   HTML4)    PDF (782KB)(364)      
    The finite temperature Lanczos method (FTLM), which is an exact diagonalization method intensively used in quantum many-body calculations, is formulated in the framework of orthogonal polynomials and Gauss quadrature. The main idea is to reduce finite temperature static and dynamic quantities into weighted summations related to one- and two-dimensional Gauss quadratures. Then lower order Gauss quadrature, which is generated from Lanczos iteration, can be applied to approximate the initial weighted summation. This framework fills the conceptual gap between FTLM and kernel polynomial method, and makes it easy to apply orthogonal polynomial techniques in the FTLM calculation.
ISSN 1674-1056   CN 11-5639/O4

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