19 August 2021, Volume 30 Issue 9
SPECIAL TOPIC—Two-dimensional magnetic materials and devices
 Magnetic and electronic properties of two-dimensional metal-organic frameworks TM3(C2NH)12 Zhen Feng(冯振), Yi Li(李依), Yaqiang Ma(马亚强), Yipeng An(安义鹏), and Xianqi Dai(戴宪起) Chin. Phys. B, 2021, 30 (9):  097102.  DOI: 10.1088/1674-1056/ac0cdb Abstract ( 142 )   HTML ( 2 )   PDF (4889KB) ( 118 )   The ferromagnetism of two-dimensional (2D) materials has aroused great interest in recent years, which may play an important role in the next-generation magnetic devices. Herein, a series of 2D transition metal-organic framework materials (TM-NH MOF, TM=Sc-Zn) are designed, and their electronic and magnetic characters are systematically studied by means of first-principles calculations. Their structural stabilities are examined through binding energies and ab-initio molecular dynamics simulations. Their optimized lattice constants are correlated to the central TM atoms. These 2D TM-NH MOF nanosheets exhibit various electronic and magnetic performances owing to the effective charge transfer and interaction between TM atoms and graphene linkers. Interestingly, Ni- and Zn-NH MOFs are nonmagnetic semiconductors (SM) with band gaps of 0.41 eV and 0.61 eV, respectively. Co- and Cu-NH MOFs are bipolar magnetic semiconductors (BMS), while Fe-NH MOF monolayer is a half-semiconductor (HSM). Furthermore, the elastic strain could tune their magnetic behaviors and transformation, which ascribes to the charge redistribution of TM-3d states. This work predicts several new 2D magnetic MOF materials, which are promising for applications in spintronics and nanoelectronics.
 Vertical WS2 spin valve with Ohmic property based on Fe3GeTe2 electrodes Ce Hu(胡策), Faguang Yan(闫法光), Yucai Li(李予才), and Kaiyou Wang(王开友) Chin. Phys. B, 2021, 30 (9):  097505.  DOI: 10.1088/1674-1056/ac078b Abstract ( 120 )   HTML ( 1 )   PDF (628KB) ( 135 )   The two-dimensional (2D) transition-metal dichalcogenides (TMDCs) have been recently proposed as a promising class of materials for spintronic applications. Here, we report on the all-2D van der Waals (vdW) heterostructure spin valve device comprising of an exfoliated ultra-thin WS2 semiconductor acting as the spacer layer and two exfoliated ferromagnetic Fe3GeTe2 (FGT) metals acting as ferromagnetic electrodes. The metallic interface rather than Schottky barrier is formed despite the semiconducting nature of WS2, which could be originated from the strong interface hybridization. The spin valve effect persists up to the Curie temperature of FGT. Moreover, our metallic spin valve devices exhibit robust spin valve effect where the magnetoresistance magnitude does not vary with the applied bias in the measured range up to 50 μA due to the Ohmic property, which is a highly desirable feature for practical application that requires stable device performance. Our work reveals that WS2-based all-2D magnetic vdW heterostructure, facilitated by combining 2D magnets, is expected to be an attractive candidate for the TMDCs-based spintronic applications.
 Spin orbit torques in Pt-based heterostructures with van der Waals interface Qian Chen(陈倩), Weiming Lv(吕伟明), Shangkun Li(李尚坤), Wenxing Lv(吕文星), Jialin Cai(蔡佳林), Yonghui Zhu(朱永慧), Jiachen Wang(王佳晨), Rongxin Li(李荣鑫), Baoshun Zhang(张宝顺), and Zhongming Zeng(曾中明) Chin. Phys. B, 2021, 30 (9):  097506.  DOI: 10.1088/1674-1056/ac0908 Abstract ( 96 )   HTML ( 1 )   PDF (1182KB) ( 91 )   Spin orbit torques (SOTs) in ferromagnet/heavy-metal heterostructures have provided great opportunities for efficient manipulation of spintronic devices. However, deterministically field-free switching of perpendicular magnetization with SOTs is forbidden because of the global two-fold rotational symmetry in conventional heavy-metal such as Pt. Here, we engineer the interface of Pt/Ni heterostructures by inserting a monolayer MoTe2 with low crystal symmetry. It is demonstrated that the spin orbit efficiency, as well as the out-of-plane magnetic anisotropy and the Gilbert damping of Ni are enhanced, due to the effect of orbital hybridization and the increased spin scatting at the interface induced by MoTe2. Particularly, an out-of-plane damping-like torque is observed when the current is applied perpendicular to the mirror plane of the MoTe2 crystal, which is attributed to the interfacial inversion symmetry breaking of the system. Our work provides an effective route for engineering the SOT in Pt-based heterostructures, and offers potential opportunities for van der Waals interfaces in spintronic devices.
 Strain drived band aligment transition of the ferromagnetic VS2/C3N van der Waals heterostructure Jimin Shang(商继敏), Shuai Qiao(乔帅), Jingzhi Fang(房景治), Hongyu Wen(文宏玉), and Zhongming Wei(魏钟鸣) Chin. Phys. B, 2021, 30 (9):  097507.  DOI: 10.1088/1674-1056/ac0cd1 Abstract ( 82 )   HTML ( 0 )   PDF (3542KB) ( 169 )   Exploring two-dimensional (2D) magnetic heterostructures is essential for future spintronic and optoelectronic devices. Herein, using first-principle calculations, stable ferromagnetic ordering and colorful electronic properties are established by constructing the VS2/C3N van der Waals (vdW) heterostructure. Unlike the semiconductive properties with indirect band gaps in both the VS2 and C3N monolayers, our results indicate that a direct band gap with type-Ⅱ band alignment and p-doping characters are realized in the spin-up channel of the VS2/C3N heterostructure, and a typical type-Ⅲ band alignment with a broken-gap in the spin-down channel. Furthermore, the band alignments in the two spin channels can be effectively tuned by applying tensile strain. An interchangement between the type-Ⅱ and type-Ⅲ band alignments occurs in the two spin channels, as the tensile strain increases to 4%. The attractive magnetic properties and the unique band alignments could be useful for prospective applications in the next-generation tunneling devices and spintronic devices.
 Controlled vapor growth of 2D magnetic Cr2Se3 and its magnetic proximity effect in heterostructures Danliang Zhang(张丹亮), Chen Yi(易琛), Cuihuan Ge(葛翠环), Weining Shu(舒维宁), Bo Li(黎博), Xidong Duan(段曦东), Anlian Pan(潘安练), and Xiao Wang(王笑) Chin. Phys. B, 2021, 30 (9):  097601.  DOI: 10.1088/1674-1056/ac0cd9 Abstract ( 136 )   HTML ( 2 )   PDF (3458KB) ( 216 )   Two-dimensional (2D) magnetic materials have aroused tremendous interest due to the 2D confinement of magnetism and potential applications in spintronic and valleytronic devices. However, most of the currently 2D magnetic materials are achieved by the exfoliation from their bulks, of which the thickness and domain size are difficult to control, limiting the practical device applications. Here, we demonstrate the realization of thickness-tunable rhombohedral Cr2Se3 nanosheets on different substrates via the chemical vapor deposition route. The magnetic transition temperature at about 75 K is observed. Furthermore, van der Waals heterostructures consisting of Cr2Se3 nanosheets and monolayer WS2 are constructed. We observe the magnetic proximity effect in the heterostructures, which manifests the manipulation of the valley polarization in monolayer WS2. Our work contributes to the vapor growth and applications of 2D magnetic materials.
REVIEW
 Signal-to-noise ratio of Raman signal measured by multichannel detectors Xue-Lu Liu(刘雪璐), Yu-Chen Leng(冷宇辰), Miao-Ling Lin(林妙玲), Xin Cong(从鑫), and Ping-Heng Tan(谭平恒) Chin. Phys. B, 2021, 30 (9):  097807.  DOI: 10.1088/1674-1056/ac1f06 Abstract ( 99 )   HTML ( 0 )   PDF (1856KB) ( 89 )   Raman spectroscopy has been widely used to characterize the physical properties of two-dimensional materials (2DMs). The signal-to-noise ratio (SNR or S/N ratio) of Raman signal usually serves as an important indicator to evaluate the instrumental performance rather than Raman intensity itself. Multichannel detectors with outstanding sensitivity, rapid acquisition speed and low noise level have been widely equipped in Raman instruments for the measurement of Raman signal. In this mini-review, we first introduce the recent advances of Raman spectroscopy of 2DMs. Then we take the most commonly used CCD detector and IGA array detector as examples to overview the various noise sources in Raman measurements and analyze their potential influences on SNR of Raman signal in experiments. This overview can contribute to a better understanding on the SNR of Raman signal and the performance of multichannel detector for numerous researchers and instrumental design for industry, as well as offer practical strategies for improving spectral quality in routine measurement.
RAPID COMMUNICATION
 First neutron Bragg-edge imaging experimental results at CSNS Hot! Jie Chen(陈洁), Zhijian Tan(谭志坚), Weiqiang Liu(刘玮强), Sihao Deng(邓司浩), Shengxiang Wang(王声翔), Liyi Wang(王立毅), Haibiao Zheng(郑海彪), Huaile Lu(卢怀乐), Feiran Shen(沈斐然), Jiazheng Hao(郝嘉政), Xiaojuan Zhou(周晓娟), Jianrong Zhou(周健荣), Zhijia Sun(孙志嘉), Lunhua He(何伦华), and Tianjiao Liang(梁天骄) Chin. Phys. B, 2021, 30 (9):  096106.  DOI: 10.1088/1674-1056/ac0da7 Abstract ( 204 )   HTML ( 0 )   PDF (1294KB) ( 272 )   The neutron Bragg-edge imaging is expected to be a new non-destructive energy-resolved neutron imaging technique for quantitatively two-dimensional or three-dimensional visualizing crystallographic information in a bulk material, which could be benefited from pulsed neutron source. Here we build a Bragg-edge imaging system on the General Purpose Powder Diffractometer at the China Spallation Neutron Source. The residual strain mapping of a bent Q235 ferrite steel sample has been achieved with a spectral resolution of 0.15% by the time-of-flight neutron Bragg-edge imaging on this system. The results show its great potential applications in materials science and engineering.
 Passivation and dissociation of Pb-type defects at a-SiO2/Si interface Xue-Hua Liu(刘雪华), Wei-Feng Xie(谢伟锋), Yang Liu(刘杨), and Xu Zuo(左旭) Chin. Phys. B, 2021, 30 (9):  097101.  DOI: 10.1088/1674-1056/ac0e20 Abstract ( 63 )   HTML ( 0 )   PDF (1880KB) ( 52 )   It is well known that in the process of thermal oxidation of silicon, there are Pb-type defects at amorphous silicon dioxide/silicon (a-SiO2/Si) interface due to strain. These defects have a very important impact on the performance and reliability of semiconductor devices. In the process of passivation, hydrogen is usually used to inactivate Pb-type defects by the reaction Pb+H2→PbH+H. At the same time, PbH centers dissociate according to the chemical reaction PbH→Pb+H. Therefore, it is of great significance to study the balance of the passivation and dissociation. In this work, the reaction mechanisms of passivation and dissociation of the Pb-type defects are investigated by first-principles calculations. The reaction rates of the passivation and dissociation are calculated by the climbing image-nudged elastic band (CI-NEB) method and harmonic transition state theory (HTST). By coupling the rate equations of the passivation and dissociation reactions, the equilibrium density ratio of the saturated interfacial dangling bonds and interfacial defects (Pb, Pb0, and Pb1) at different temperatures is calculated.
 Revealing the A1g-type strain effect on superconductivity and nematicity in FeSe thin flake Hot! Zhaohui Cheng(程朝晖), Bin Lei(雷彬), Xigang Luo(罗习刚), Jianjun Ying(应剑俊), Zhenyu Wang(王震宇), Tao Wu(吴涛), and Xianhui Chen(陈仙辉) Chin. Phys. B, 2021, 30 (9):  097403.  DOI: 10.1088/1674-1056/ac1efa Abstract ( 173 )   HTML ( 0 )   PDF (1879KB) ( 241 )   The driving mechanism of nematicity and its twist with superconductivity in iron-based superconductors are still under debate. Recently, a dominant B1g-type strain effect on superconductivity is observed in underdoped iron-pnictides superconductors Ba(Fe1-xCox)2As2, suggesting a strong interplay between nematicity and superconductivity. Since the long-range spin order is absent in FeSe superconductor, whether a similar strain effect could be also observed or not is an interesting question. Here, by utilizing a flexible film as substrate, we successfully achieve a wide-range-strain tuning of FeSe thin flake, in which both the tensile and compressive strain could reach up to ～0.7%, and systematically study the strain effect on both superconducting and nematic transition (Tc and Ts) in the FeSe thin flake. Our results reveal a predominant A1g-type strain effect on Tc. Meanwhile, Ts exhibits a monotonic anti-correlation with Tc and the maximum Tc reaches to 12 K when Ts is strongly suppressed under the maximum compressive strain. Finally, in comparison with the results in the underdoped Ba(Fe1-xCox)2As2, the absence of B1g-type strain effect in FeSe further supports the role of stripe-type spin fluctuations on superconductivity. In addition, our work also supports that the orbital degree of freedom plays a key role to drive the nematic transition in FeSe.
 Optimized growth of compensated ferrimagnetic insulator Gd3Fe5O12 with a perpendicular magnetic anisotropy Heng-An Zhou(周恒安), Li Cai(蔡立), Teng Xu(许腾), Yonggang Zhao(赵永刚), and Wanjun Jiang(江万军) Chin. Phys. B, 2021, 30 (9):  097503.  DOI: 10.1088/1674-1056/ac0db0 Abstract ( 80 )   HTML ( 0 )   PDF (2202KB) ( 63 )   Compensated ferrimagnetic insulators are particularly interesting for enabling functional spintronic, optical, and microwave devices. Among many different garnets, Gd3Fe5O12 (GdIG) is a representative compensated ferrimagnetic insulator. In this paper, we will study the evolution of the surface morphology, the magnetic properties, and the magnetization compensation through changing the following parameters: the annealing temperature, the growth temperature, the annealing duration, and the choice of different single crystalline garnet substrates. Our objective is to find the optimized growth condition of the GdIG films, for the purpose of achieving a strong perpendicular magnetic anisotropy (PMA) and a flat surface, together with a small effective damping parameter. Through our experiments, we have found that the surface roughness approaching 0.15 nm can be obtained by choosing the growth temperature around 700 ℃, together with an enhanced PMA. We have also found the modulation of magnetic anisotropy by choosing different single crystalline garnet substrates which change the tensile strain to the compressive strain. A measure of the effective magnetic damping parameter (αeff=0.04±0.01) through a spin pumping experiment in a GdIG/Pt bilayer is also made. Through optimizing the growth dynamics of GdIG films, our results could be useful for synthesizing garnet films with a PMA, which could be beneficial for the future development of ferrimagnetic spintronics.
 Gate-controlled magnetic transitions in Fe3GeTe2 with lithium ion conducting glass substrate Hot! 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 Abstract ( 359 )   HTML ( 0 )   PDF (806KB) ( 434 )   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.
 Ultrafast structural dynamics using time-resolved x-ray diffraction driven by relativistic laser pulses Hot! Chang-Qing Zhu(朱常青), Jun-Hao Tan(谭军豪), Yu-Hang He(何雨航), Jin-Guang Wang(王进光), Yi-Fei Li(李毅飞), Xin Lu(鲁欣), Ying-Jun Li(李英骏), Jie Chen(陈洁), Li-Ming Chen(陈黎明), and Jie Zhang(张杰) Chin. Phys. B, 2021, 30 (9):  098701.  DOI: 10.1088/1674-1056/ac0baf Abstract ( 246 )   HTML ( 0 )   PDF (2226KB) ( 184 )   Based on a femtosecond laser plasma-induced hard x-ray source with a high laser pulse energy (>100 mJ) at 10 Hz repetition rate, we present a time-resolved x-ray diffraction system on an ultrafast time scale. The laser intensity is at relativistic regime (2×1019 W/cm2), which is essential for effectively generating Kα source in high-Z metal material. The produced copper Kα radiation yield reaches to 2.5×108 photons/sr/shot. The multilayer mirrors are optimized for monochromatizating and two-dimensional beam shaping of Kα emission. Our experiment exhibits its ability of monitoring the transient structural changes in a thin film SrCoO2.5 crystal. It is demonstrated that this facility is a powerful tool to perform dynamic studies on samples and adaptable to the specific needs for different particular applications with high flexibility.
GENERAL
 Multiple solutions and hysteresis in the flows driven by surface with antisymmetric velocity profile Xiao-Feng Shi(石晓峰), Dong-Jun Ma(马东军), Zong-Qiang Ma(马宗强), De-Jun Sun(孙德军), and Pei Wang(王裴) Chin. Phys. B, 2021, 30 (9):  090201.  DOI: 10.1088/1674-1056/abf7a6 Abstract ( 83 )   HTML ( 0 )   PDF (753KB) ( 36 )   Multiple steady solutions and hysteresis phenomenon in the square cavity flows driven by the surface with antisymmetric velocity profile are investigated by numerical simulation and bifurcation analysis. A high order spectral element method with the matrix-free pseudo-arclength technique is used for the steady-state solution and numerical continuation. The complex flow patterns beyond the symmetry-breaking at Re≈320 are presented by a bifurcation diagram for Re<2500. The results of stable symmetric and asymmetric solutions are consistent with those reported in literature, and a new unstable asymmetric branch is obtained besides the stable branches. A novel hysteresis phenomenon is observed in the range of 2208 < Re < 2262, where two pairs of stable and two pairs of unstable asymmetric steady solutions beyond the stable symmetric state coexist. The vortices near the sidewall appear when the Reynolds number increases, which correspond to the bifurcation of topology structure, but not the bifurcation of Navier-Stokes equations. The hysteresis is proposed to be the result of the combined mechanisms of the competition and coalescence of secondary vortices.
 Magnetization relaxation of uniaxial anisotropic ferromagnetic particles with linear reaction dynamics driven by DC/AC magnetic field Yu-Song Hu(胡玉松), Min Jiang(江敏), Tao Hong(洪涛), Zheng-Ming Tang(唐正明), and Ka-Ma Huang(黄卡玛) Chin. Phys. B, 2021, 30 (9):  090202.  DOI: 10.1088/1674-1056/abeb0b Abstract ( 37 )   HTML ( 0 )   PDF (627KB) ( 17 )   The response of uniaxial anisotropic ferromagnetic particles with linear reaction dynamics subjected to alternating current (AC) or direct current (DC) bias magnetic field is evaluated by the reaction-diffusion equation for the probability distribution function of the molecular concentration in the spherical coordinate system. The magnetization function and the probability distribution function of the magnetic particles in the reaction system are derived by using the Legendre polynomials and Laplace transform. We discuss the characteristics of magnetization and probability distribution of the magnetic particles with different anisotropic parameters driven by a DC and AC magnetic fields, respectively. It is shown that both the magnetization and the probability distribution decrease with time increasing due to the reaction process. The uniformity of the probability distribution and the amplitude of the magnetization are both affected by the anisotropic parameters. Meanwhile, the difference between the case with linear reaction dynamics and the non-reaction case is discussed.
 Influences of spin-orbit interaction on quantum speed limit and entanglement of spin qubits in coupled quantum dots M Bagheri Harouni Chin. Phys. B, 2021, 30 (9):  090301.  DOI: 10.1088/1674-1056/abeef4 Abstract ( 56 )   HTML ( 0 )   PDF (672KB) ( 13 )   Quantum speed limit and entanglement of a two-spin Heisenberg XYZ system in an inhomogeneous external magnetic field are investigated. The physical system studied is the excess electron spin in two adjacent quantum dots. The influences of magnetic field inhomogeneity as well as spin-orbit coupling are studied. Moreover, the spin interaction with surrounding magnetic environment is investigated as a non-Markovian process. The spin-orbit interaction provides two important features: the formation of entanglement when two qubits are initially in a separated state and the degradation and rebirth of the entanglement.
 Quantum multicast schemes of different quantum states via non-maximally entangled channels with multiparty involvement Yan Yu(于妍), Nan Zhao(赵楠), Chang-Xing Pei(裴昌幸), and Wei Li(李玮) Chin. Phys. B, 2021, 30 (9):  090302.  DOI: 10.1088/1674-1056/abeef2 Abstract ( 57 )   HTML ( 0 )   PDF (1192KB) ( 28 )   Due to the unavoidable interaction between the quantum channel and its ambient environment, it is difficult to generate and maintain the maximally entanglement. Thus, the research on multiparty information transmission via non-maximally entangled channels is of academic value and general application. Here, we utilize the non-maximally entangled channels to implement two multiparty remote state preparation schemes for transmitting different quantum information from one sender to two receivers synchronously. The first scheme is adopted to transmit two different four-qubit cluster-type entangled states to two receivers with a certain probability. In order to improve success probabilities of such multicast remote state preparation using non-maximally entangled channels, we put forward the second scheme, which deals with the situation that is a synchronous transfer of an arbitrary single-qubit state and an arbitrary two-qubit state from one sender to two receivers. In particular, its success probability can reach 100% in principle, and independent of the entanglement degree of the shared non-maximally entangled channel. Notably, in the second scheme, the auxiliary particle is not required.
 Preparation of a two-state mixture of ultracold fermionic atoms with balanced population subject to the unstable magnetic field Donghao Li(李东豪), Lianghui Huang(黄良辉), Guoqi Bian(边国旗), Jie Miao(苗杰), Liangchao Chen(陈良超), Zengming Meng(孟增明), Wei Han(韩伟), and Pengjun Wang(王鹏军) Chin. Phys. B, 2021, 30 (9):  090303.  DOI: 10.1088/1674-1056/abee6e Abstract ( 61 )   HTML ( 0 )   PDF (1595KB) ( 16 )   We report a novel method to prepare a mixture of 40K Fermi gas having an equal population of the two ground magnetic spin states confined in an optical dipole trap, in the presence of an noisy quantization (magnetic) field. We realize the equal population mixture by applying a series of RF pulses. We observe the dependence of the population distribution between two spin states on the number of the applied RF pulses and find that the decoherence effects leading to the population fluctuations are overcome by the high number of RF pules. Our demonstrated technique can be potentially used in the precision measurement experiments with ultracold gases in noisy environments.
 Quantum metrology with coherent superposition of two different coded channels Dong Xie(谢东), Chunling Xu(徐春玲), and Anmin Wang(王安民) Chin. Phys. B, 2021, 30 (9):  090304.  DOI: 10.1088/1674-1056/ac0bae Abstract ( 63 )   HTML ( 0 )   PDF (586KB) ( 60 )   We investigate the advantage of coherent superposition of two different coded channels in quantum metrology. In a continuous variable system, we show that the Heisenberg limit 1/N can be beaten by the coherent superposition without the help of indefinite causal order. And in parameter estimation, we demonstrate that the strategy with the coherent superposition can perform better than the strategy with quantum switch which can generate indefinite causal order. We analytically obtain the general form of estimation precision in terms of the quantum Fisher information and further prove that the nonlinear Hamiltonian can improve the estimation precision and make the measurement uncertainty scale as 1/Nm for m≥2. Our results can help to construct a high-precision measurement equipment, which can be applied to the detection of coupling strength and the test of time dilation and the modification of the canonical commutation relation.
 An optimized cluster density matrix embedding theory Hao Geng(耿浩) and Quan-lin Jie(揭泉林) Chin. Phys. B, 2021, 30 (9):  090305.  DOI: 10.1088/1674-1056/ac0cdc Abstract ( 58 )   HTML ( 0 )   PDF (1532KB) ( 66 )   We propose an optimized cluster density matrix embedding theory (CDMET). It reduces the computational cost of CDMET with simpler bath states. And the result is as accurate as the original one. As a demonstration, we study the distant correlations of the Heisenberg J1-J2 model on the square lattice. We find that the intermediate phase (0.43≤sssim J2≤sssim 0.62) is divided into two parts. One part is a near-critical region (0.43≤J2≤0.50). The other part is the plaquette valence bond solid (PVB) state (0.51≤J2≤0.62). The spin correlations decay exponentially as a function of distance in the PVB.
 Entanglement of two distinguishable atoms in a rectangular waveguide: Linear approximation with single excitation Jing Li(李静), Lijuan Hu(胡丽娟), Jing Lu(卢竞), and Lan Zhou(周兰) Chin. Phys. B, 2021, 30 (9):  090307.  DOI: 10.1088/1674-1056/ac0bb3 Abstract ( 33 )   HTML ( 0 )   PDF (1130KB) ( 22 )   We investigate the entanglement dynamics of two distinguishable two-level systems (TLSs) characterized by energy difference δ located inside a rectangular hollow metallic waveguide of transverse dimensions a and b. The effects of energy difference δ and the inter-TLS distance on the time evolution of the concurrence of the TLSs are examined in the single excitation subspace when the energy separation of the TLS is far away from the cutoff frequencies of the transverse mode.
 Quantum speed limit for the maximum coherent state under the squeezed environment Kang-Ying Du(杜康英), Ya-Jie Ma(马雅洁), Shao-Xiong Wu(武少雄), and Chang-Shui Yu(于长水) Chin. Phys. B, 2021, 30 (9):  090308.  DOI: 10.1088/1674-1056/ac0daf Abstract ( 74 )   HTML ( 0 )   PDF (715KB) ( 68 )   The quantum speed limit time for quantum system under squeezed environment is studied. We consider two typical models, the damped Jaynes-Cummings model and the dephasing model. For the damped Jaynes-Cummings model under squeezed environment, we find that the quantum speed limit time becomes larger with the squeezed parameter r increasing and indicates symmetry about the phase parameter value θ=π. Meanwhile, the quantum speed limit time can also be influenced by the coupling strength between the system and environment. However, the quantum speed limit time for the dephasing model is determined by the dephasing rate and the boundary of acceleration region that interacting with vacuum reservoir can be broken when the squeezed environment parameters are appropriately chosen.
 Identification of unstable individuals in dynamic networks Dongli Duan(段东立), Tao Chai(柴涛), Xixi Wu(武茜茜), Chengxing Wu(吴成星), Shubin Si(司书宾), and Genqing Bian(边根庆) Chin. Phys. B, 2021, 30 (9):  090501.  DOI: 10.1088/1674-1056/abe92f Abstract ( 47 )   HTML ( 0 )   PDF (703KB) ( 32 )   To identify the unstable individuals of networks is of great importance for information mining and security management. Exploring a broad range of steady-state dynamical processes including biochemical dynamics, epidemic processes, birth-death processes and regulatory dynamics, we propose a new index from the microscopic perspective to measure the stability of network nodes based on the local correlation matrix. The proposed index describes the stability of each node based on the activity change of the node after its neighbor is disturbed. Simulation and comparison results show our index can identify the most unstable nodes in the network with various dynamical behaviors, which would actually create a richer way and a novel insight of exploring the problem of network controlling and optimization.
 Migration and shape of cells on different interfaces Xiaochen Wang(王晓晨), Qihui Fan (樊琪慧), and Fangfu Ye(叶方富) Chin. Phys. B, 2021, 30 (9):  090502.  DOI: 10.1088/1674-1056/abf557 Abstract ( 34 )   HTML ( 0 )   PDF (1266KB) ( 10 )   Impacts of microenvironments on cell migration have been reported in various interaction modes. A rapid tumor metastasis occurs along topological interfaces in vivo, such as the interface between the blood vessels and nerves. In this work, we culture MDA-MB231 cells at dish-liquid, dish-hydrogel, and hydrogel-liquid interfaces, respectively, to study how these different interfaces influence cell dynamics and morphology. Our results show that the migration mode of cells changes from an amoeboid motion to a mesenchymal motion but their speed do not change obviously if the interface changes from hydrogel-liquid to dish-liquid. In contrast, the migration mode of cells at a dish-hydrogel interface maintains as a mesenchymal motion, whereas their speed increases significantly.
 Nonlinear vibration of iced cable under wind excitation using three-degree-of-freedom model Wei Zhang(张伟), Ming-Yuan Li(李明远), Qi-Liang Wu(吴启亮), and An Xi(袭安) Chin. Phys. B, 2021, 30 (9):  090503.  DOI: 10.1088/1674-1056/abea83 Abstract ( 42 )   HTML ( 0 )   PDF (2268KB) ( 13 )   High-voltage transmission line possesses a typical suspended cable structure that produces ice in harsh weather. Moreover, transversely galloping will be excited due to the irregular structure resulting from the alternation of lift force and drag force. In this paper, the nonlinear dynamics and internal resonance of an iced cable under wind excitation are investigated. Considering the excitation caused by pulsed wind and the movement of the support, the nonlinear governing equations of motion of the iced cable are established using a three-degree-of-freedom model based on Hamilton's principle. By the Galerkin method, the partial differential equations are then discretized into ordinary differential equations. The method of multiple scales is then used to obtain the averaged equations of the iced cable, and the principal parametric resonance-1/2 subharmonic resonance and the 2:1 internal resonance are considered. The numerical simulations are performed to investigate the dynamic response of the iced cable. It is found that there exist periodic, multi-periodic, and chaotic motions of the iced cable subjected to wind excitation.
 Detection of multi-spin interaction of a quenched XY chain by the average work and the relative entropy Xiu-Xing Zhang(张修兴), Fang-Jv Li(李芳菊), Kai Wang(王凯), Jing Xue(薛晶), Guang-Wen Huo(霍广文), Ai-Ping Fang(方爱平), and Hong-Rong Li(李宏荣) Chin. Phys. B, 2021, 30 (9):  090504.  DOI: 10.1088/1674-1056/abeef5 Abstract ( 52 )   HTML ( 0 )   PDF (799KB) ( 10 )   We investigate the nonequilibrium thermodynamics of a quenched XY spin chain with multi-spin interaction in a transverse field. The analytical expressions of both the average work and the relative entropy are obtained under different quenching parameters. The influences of the system parameters on the nonequilibrium thermodynamics are investigated. We find that at finite temperature the critical phenomenon induced by the multi-spin interaction and the external field can be revealed by the properties of the system nonequilibrium thermodynamics. In addition, our results indicate that the average work and the relative entropy can be used to detect both the existence and strength of the multi-spin interaction in the nonequlibrium system.
 Nonlinear dynamics of cell migration in anisotropic microenvironment Yanping Liu(刘艳平), Da He(何达), Yang Jiao(焦阳), Guoqiang Li(李国强), Yu Zheng(郑钰), Qihui Fan(樊琪慧), Gao Wang(王高), Jingru Yao(姚静如), Guo Chen(陈果), Silong Lou(娄四龙), and Liyu Liu(刘雳宇) Chin. Phys. B, 2021, 30 (9):  090505.  DOI: 10.1088/1674-1056/ac11d5 Abstract ( 48 )   HTML ( 0 )   PDF (1844KB) ( 55 )   Cell migration in anisotropic microenvironment plays an important role in the development of normal tissues and organs as well as neoplasm progression, e.g., osteogenic differentiation of embryonic stem cells was facilitated on stiffer substrates, indicating that the mechanical signals greatly affect both early and terminal differentiation of embryonic stem cells. However, the effect of anisotropy on cell migration dynamics, in particular, in terms of acceleration profiles which is important for recognizing dynamics modes of cell migration and analyzing the regulation mechanisms of microenvironment in mechanical signal transmission, has not been systematically investigated. In this work, we firstly rigorously investigate and quantify the differences between persistent random walk and anisotropic persistent random walk models based on the analysis of cell migration trajectories and velocity auto-covariance function, both qualitatively and quantitatively. Secondly, we introduce the concepts of positive and negative anisotropy based on the motility parameters to study the effect of anisotropy on acceleration profiles, especially the nonlinear decrease and non-monotonic behaviors. We particularly elaborate and discuss the mechanisms, and physical insights of non-monotonic behaviors in the case of positive anisotropy, focusing on the force exerted on migrating cells. Finally, we analyze two types of in vitro cell migration experiments and verify the universality of nonlinear decrease and the consistence of non-monotonic behaviors with numerical results. We conclude that the anisotropy of microenvironment is the cause of the non-monotonic and nonlinear dynamics, and the anisotropic persistent random walk can be as a suitable tool to analyze in vitro cell migration with different combinations of motility parameters. Our analysis provides new insights into the dynamics of cell migration in complex microenvironment, which also has implications in tissue engineering and cancer research.
 Ferromagnetic Heisenberg spin chain in a resonator Yusong Cao(曹雨松), Junpeng Cao(曹俊鹏), and Heng Fan(范桁) Chin. Phys. B, 2021, 30 (9):  090506.  DOI: 10.1088/1674-1056/ac1334 Abstract ( 86 )   HTML ( 0 )   PDF (503KB) ( 68 )   We investigate the properties of a generalized Rabi model by replacing the two-level atom in Rabi model with a ferromagnetic Heisenberg spin chain. We find that the dynamical behavior of the system can be divided into four categories. The energy spectrum of the ground state and some low excited states are obtained. When the magnons and the photon are in resonance, the model is exactly solvable and the rigorous solution is obtained. Near the resonance point where the detuning is small, the system is studied with the help of perturbation theory. This model has a spontaneously breaking of parity symmetry, suggesting the existence of a quantum phase transition. The critical exponent from the normal phase is computed.
 Dynamic modeling and aperiodically intermittent strategy for adaptive finite-time synchronization control of the multi-weighted complex transportation networks with multiple delays Ning Li(李宁), Haiyi Sun(孙海义), Xin Jing(靖新), and Zhongtang Chen(陈仲堂) Chin. Phys. B, 2021, 30 (9):  090507.  DOI: 10.1088/1674-1056/abea92 Abstract ( 52 )   HTML ( 0 )   PDF (763KB) ( 21 )   The idea of network splitting according to time delay and weight is introduced. Based on the cyber physical systems (CPS), a class of multi-weighted complex transportation networks with multiple delays is modeled. The finite-time synchronization of the proposed complex transportation networks model is studied systematically. On the basis of the theory of stability, the technique of adaptive control, aperiodically intermittent control and finite-time control, the aperiodically intermittent adaptive finite-time synchronization controller is designed. The controller designed in this paper is beneficial for understanding the synchronization in multi-weighted complex transportation networks with multiple delays. In addition, the conditions for the existence of finite time synchronization have been discussed in detail. And the specific value of the settling finite time for synchronization is obtained. Moreover, the outer coupling configuration matrices are not required to be irreducible or symmetric. Finally, simulation results of the finite-time synchronization problem are given to illustrate the correctness of the results obtained.
 Design of an ultrafast electron diffractometer with multiple operation modes Chun-Long Hu(胡春龙), Zhong Wang(王众), Yi-Jie Shi(石义杰), Chang Ye(叶昶), and Wen-Xi Liang(梁文锡) Chin. Phys. B, 2021, 30 (9):  090701.  DOI: 10.1088/1674-1056/ac11cd Abstract ( 54 )   HTML ( 0 )   PDF (1462KB) ( 31 )   Directly resolving structural changes in material on the atomic scales of time and space is desired in studies of many disciplines. Ultrafast electron diffraction (UED), which combines the temporal resolution of femtosecond-pulse laser and the spatial sensitivity of electron diffraction, is an advancing methodology serving such a goal. Here we present the design of a UED apparatus with multiple operation modes for observation of collective atomic motions in solid material of various morphologies. This multi-mode UED employs a pulsed electron beam with propagation trajectory of parallel and convergent incidences, and diffraction configurations of transmission and reflection, as well utilities of preparation and characterization of cleaned surface and adsorbates. We recorded the process of electron-phonon coupling in single crystal molybdenum ditelluride following excitation of femtosecond laser pulses, and diffraction patterns of polycrystalline graphite thin film under different settings of electron optics, to demonstrate the temporal characteristics and tunable probe spot of the built UED apparatus, respectively.
ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
 Terahertz radiation generation by beating of two chirped laser pulses in a warm collisional magnetized plasma Motahareh Arefnia, Mehdi Sharifian, and Mohammad Ghorbanalilu Chin. Phys. B, 2021, 30 (9):  094101.  DOI: 10.1088/1674-1056/abfb5d Abstract ( 65 )   HTML ( 0 )   PDF (1489KB) ( 27 )   Analytical equations of terahertz (THz) radiation generation based on beating of two laser beams in a warm collisional magnetized plasma with a ripple density profile are developed. In this regard, the effects of frequency chirp on the field amplitude of the terahertz radiation as well as the temperature and collision parameters are investigated. The ponderomotive force is generated in the frequency chirp of beams. Resonant excitation depends on tuning of the plasma beat frequency, magnetic field frequency, thermal velocity, collisional frequency, and effect of the frequency chirp with the plasma density. For optimum parameters of frequency and temperature the maximum THz amplitude is obtained.
 Possibility to break through limitation of measurement range in dual-wavelength digital holography Tuo Li(李拓), Wen-Xiu Lei(雷文秀), Xin-Kai Sun(孙鑫凯), Jun Dong(董军), Ye Tao(陶冶), and Yi-Shi Shi(史祎诗) Chin. Phys. B, 2021, 30 (9):  094201.  DOI: 10.1088/1674-1056/abf348 Abstract ( 49 )   HTML ( 0 )   PDF (3486KB) ( 30 )   By using the beat frequency technique, the dual-wavelength digital holography (DWDH) can greatly increase the measurement range of the system. However, the beat frequency technique has a limitation in measurement range. The measurement range is not larger than a synthetic wavelength. Here, to break through this limitation, we propose a novel DWDH method based on the constrained underdetermined equations, which consists of three parts: (i) prove that the constrained underdetermined equation has a unique integer solution, (ii) design an algorithm to search for the unique integer solution, (iii) introduce a third wavelength into the DWDH system, and design a corresponding algorithm to enhance the anti-noise performance of DWDH. As far as we know, it is the first time that we have discovered that the problem of DWDH can belong in a problem of contained underdetermined equations, and it is also the first time that we have given the mathematical proof for breaking through the limitation of the measurement range. A series of results is shown to test the theory and the corresponding algorithms. More importantly, since the principle of proposed DWDH is based on basic mathematical principles, it can be further extended to various fields, such as dual-wavelength microwave imaging and dual-wavelength coherent diffraction imaging.
 High-resolution three-dimensional atomic microscopy via double electromagnetically induced transparency Abdul Wahab Chin. Phys. B, 2021, 30 (9):  094202.  DOI: 10.1088/1674-1056/abf0fd Abstract ( 48 )   HTML ( 0 )   PDF (3417KB) ( 14 )   We aim to present a new scheme for high-dimensional atomic microscopy via double electromagnetically induced transparency in a four-level tripod system. For atom-field interaction, we construct a spatially dependent field by superimposing three standing-wave fields (SWFs) in 3D-atom localization. We achieve a high precision and high spatial resolution of an atom localization by appropriately adjusting the system variables such as field intensities and phase shifts. We also see the impact of Doppler shift and show that it dramatically deteriorates the precision of spatial information on 3D-atom localization. We believe that our suggested scheme opens up a fascinating way to improve the atom localization that supplies some practical applications in atom nanolithography, and Bose-Einstein condensation.
 Multiple induced transparency in a hybrid driven cavity optomechanical device with a two-level system Wei Zhang(张伟), Li-Guo Qin(秦立国), Li-Jun Tian(田立君), and Zhong-Yang Wang(王中阳) Chin. Phys. B, 2021, 30 (9):  094203.  DOI: 10.1088/1674-1056/abf642 Abstract ( 65 )   HTML ( 0 )   PDF (1304KB) ( 27 )   We present a scheme with the multiple-induced transparency windows in a hybrid optomechanical device. By studying the transmission of a probe field through the hybrid device, we show the successive generations of three transparent windows induced by multiple factors including tunneling, optomechanical and qubit-phonon coupling interactions, and analyze the physical mechanism of the induced transparency based on a simplified energy-level diagram of the system. Moreover, the effects of the transition frequency and decay rate of the two-level system on the multiple-induced transparency windows are discussed. We find that the transparency windows can be modulated by the coupling interaction between the qubit and NMR, the decay of qubit and the power of the control field. Therefore, the transmission of the probe field can be coherently adjusted in the hybrid cavity optomechanical device with a two-level system.
 GaSb-based type-I quantum well cascade diode lasers emitting at nearly 2-μm wavelength with digitally grown AlGaAsSb gradient layers Yi Zhang(张一), Cheng-Ao Yang(杨成奥), Jin-Ming Shang(尚金铭), Yi-Hang Chen(陈益航), Tian-Fang Wang(王天放), Yu Zhang(张宇), Ying-Qiang Xu(徐应强), Bing Liu(刘冰), and Zhi-Chuan Niu(牛智川) Chin. Phys. B, 2021, 30 (9):  094204.  DOI: 10.1088/1674-1056/abe930 Abstract ( 71 )   HTML ( 1 )   PDF (731KB) ( 23 )   We report a GaSb-based type-I quantum well cascade diode laser emitting at nearly 2-μm wavelength. The recycling of carriers is realized by the gradient AlGaAsSb barrier and chirped GaSb/AlSb/InAs electron injector. The growth of quaternary digital alloy with a gradually changed composition by short-period superlattices is introduced in detail in this paper. And the quantum well cascade laser with 100-μm-wide, 2-mm-long ridge generates an about continuous-wave output of 0.8 W at room temperature. The characteristic temperature T0 is estimated at above 60 K.
 Tunable optomechanically induced transparency and fast-slow light in a loop-coupled optomechanical system Qinghong Liao(廖庆洪), Xiaoqian Wang(王晓倩), Gaoqian He(何高倩), and Liangtao Zhou(周良涛) Chin. Phys. B, 2021, 30 (9):  094205.  DOI: 10.1088/1674-1056/ac0cda Abstract ( 39 )   HTML ( 0 )   PDF (646KB) ( 17 )   We theoretically explore the tunability of optomechanically induced transparency (OMIT) phenomenon and fast-slow light effect in a loop-coupled hybrid optomechanical system in which two optical modes are coupled to a common mechanical mode. In the probe output spectrum, we find that the interference phenomena OMIT caused by the optomechanical interactions and the normal mode splitting (NMS) induced by the strong tunnel coupling between the cavities can be observed. We further observe that the tunnel interaction will affect the distance and the heights of the sideband absorption peaks. The results also show that the switch from absorption to amplification can be realized by tuning the driving strength because of the existence of stability condition. Except from modulating the tunnel interaction, the conversion between slow light and fast light also can be achieved by adjusting the optomechanical interaction in the output field. This study may provide a potential application in the fields of high precision measurement and quantum information processing.
 All-fiber laser seeded femtosecond Yb:KGW solid state regenerative amplifier Renchong Lv(吕仁冲), Hao Teng(滕浩), Jiajun Song(宋贾俊), Renzhu Kang(康仁铸), Jiangfeng Zhu(朱江峰), and Zhiyi Wei(魏志义) Chin. Phys. B, 2021, 30 (9):  094206.  DOI: 10.1088/1674-1056/ac11d3 Abstract ( 112 )   HTML ( 0 )   PDF (1407KB) ( 75 )   A high efficiency compact Yb:KGW regenerative amplifier using an all-fiber laser seed source was comprehensively studied. With thermal lensing effect compensated by the cavity design, the compressed pulses with energy of 1 mJ at 1 kHz and 0.4 mJ at 10 kHz in sub-400-fs pulse duration using chirped fiber Bragg grating (CFBG) stretcher were demonstrated. A modified Frantz-Nodvik equation was developed to emulate the dynamic behavior of the regenerative amplifier. The simulation results were in good agreement with the experiment. Numerical simulations and experimental results show that the scheme can be scalable to higher energy of multi-mJ, sub-300 fs pulses.
 Mid-infrared supercontinuum and optical frequency comb generations in a multimode tellurite photonic crystal fiber Xu Han(韩旭), Ying Han(韩颖), Chao Mei(梅超), Jing-Zhao Guan(管景昭), Yan Wang(王彦), Lin Gong(龚琳), Jin-Hui Yuan(苑金辉), and Chong-Xiu Yu(余重秀) Chin. Phys. B, 2021, 30 (9):  094207.  DOI: 10.1088/1674-1056/abf10f Abstract ( 52 )   HTML ( 0 )   PDF (3140KB) ( 24 )   We numerically investigate the mid-infrared (MIR) supercontinuum (SC) and SC-based optical frequency comb (OFC) generations when the three optical modes (LP01, LP02, and LP12) are considered in a multimode tellurite photonic crystal fiber (MM-TPCF). The geometrical parameters of the MM-TPCF are optimized to support the multimode propagation and obtain the desired dispersion characteristics of the considered three optical modes. When the pump pulse with center wavelength λ = 2.5 μm, width T = 80 fs, and peak power P = 18 kW is coupled into the anomalous dispersion region of the LP01, LP02, and LP12 modes of the MM-TPCF, the -40-dB bandwidth of the generated MIR SCs can be up to 2.56, 1.39, and 1.12 octaves, respectively, along with good coherence. Moreover, the nonlinear dynamics of the generated SCs are analyzed. Finally, the MIR SCs-based OFCs are demonstrated when a train of 50 pulses at 1-GHz repetition rate is used as the pump source and launched into the MM-TPCF.
 Ultrabroadband mid-infrared emission from Cr2+:ZnSe-doped chalcogenide glasses prepared via hot uniaxial pressing and melt-quenching Ke-Lun Xia(夏克伦), Guang Jia(贾光), Hao-Tian Gan(甘浩天), Yi-Ming Gui(桂一鸣), Xu-Sheng Zhang(张徐生), Zi-Jun Liu(刘自军), and Xiang Shen(沈祥) Chin. Phys. B, 2021, 30 (9):  094208.  DOI: 10.1088/1674-1056/ac11eb Abstract ( 70 )   HTML ( 0 )   PDF (2479KB) ( 41 )   We reported an ultrabroadband mid-infrared (MIR) emission in the range of 1800 nm-3100 nm at room temperature (RT) from a Cr2+:ZnSe-doped chalcogenide glasses (ChGs) and studied the emission-dependent properties on the doping methods. A series of Cr2+:ZnSe/As40S57Se3 (in unit wt.%) glass-ceramics were prepared by hot uniaxial pressing (HUP) and melt-quenching methods, respectively. The glass-ceramics with MIR emission bands greater than 1000 nm were successfully prepared by both methods. The effects of matrix glass composition and grain doping concentration on the optical properties of the samples were studied. The occurrence state, morphology of the grains, and the microscopic elemental distributions were characterized using x-ray diffraction (XRD), scanning electron microscope (SEM), and energy dispersive spectrometer (EDS) analyses.
 Chirp-dependent ionization of hydrogen atoms in the presence of super-intense laser pulses Fengzheng Zhu(朱风筝), Xiaoyu Liu(刘晓煜), Yue Guo(郭月), Ningyue Wang(王宁月), Liguang Jiao(焦利光), and Aihua Liu(刘爱华) Chin. Phys. B, 2021, 30 (9):  094209.  DOI: 10.1088/1674-1056/ac192c Abstract ( 74 )   HTML ( 0 )   PDF (659KB) ( 57 )   We perform a theoretical study on dynamic interference in single photon ionization of ground state hydrogen atoms in the presence of a super-intense ultra-fast chirped laser pulse of different chirp types (equal-power and equal-FWHM laser pulses) by numerically solving the time-dependent Schrödinger equation in one dimension. We investigate the influences of peak intensity and chirp parameters on the instantaneous ionization rate and photoelectron yield, respectively. We also compare the photoelectron energy spectra for the ionization by the laser pulses with different chirp types. We find that the difference between the instantaneous ionization rates for the ionization of hydrogen atom driven by two different chirped laser pulses is originated from the difference in variation of vector potentials with time.
 Assessment of cortical bone fatigue using coded nonlinear ultrasound Duwei Liu(刘度为), Boyi Li(李博艺), Dongsheng Bi(毕东生), Tho N. H. T. Tran, Yifang Li(李义方), Dan Liu(刘丹), Ying Li(李颖), and Dean Ta(他得安) Chin. Phys. B, 2021, 30 (9):  094301.  DOI: 10.1088/1674-1056/ac0db2 Abstract ( 64 )   HTML ( 0 )   PDF (1663KB) ( 72 )   Bone fatigue accumulation is a factor leading to bone fracture, which is a progressive process of microdamage deteriorating under long-term and repeated stress. Since the microdamage of the early stage in bone is difficult to be investigated by linear ultrasound, the second harmonic generation method in nonlinear ultrasound technique is employed in this paper, which is proved to be more sensitive to microdamage. To solve the deficiency that the second harmonic component is easily submerged by noise in traditional nonlinear measurement, a weighted chirp coded sinusoidal signal was applied as the ultrasonic excitation, while pulse inversion is implemented at the receiving side. The effectiveness of this combination to improve the signal-to-noise ratio has been demonstrated by in vitro experiment. Progressive fatigue loading experiments were conducted on the cortical bone plate in vitro for microdamage generation. There was a significant increase in the slope of the acoustic nonlinearity parameter with the propagation distance (increased by 8% and 24% respectively) when the bone specimen was at a progressive level of microdamage. These results indicate that the coded nonlinear ultrasonic method might have the potential in diagnosing bone fatigue.
 Thermoacoustic assessment of hematocrit changes in human forearms Xue Wang(王雪), Rui Zhao(赵芮), Yi-Tong Peng(彭亦童), Zi-Hui Chi(迟子惠), Zhu Zheng(郑铸), En Li(李恩), Lin Huang(黄林), and Hua-Bei Jiang(蒋华北) Chin. Phys. B, 2021, 30 (9):  094302.  DOI: 10.1088/1674-1056/ac041c Abstract ( 31 )   HTML ( 0 )   PDF (1806KB) ( 8 )   Abnormal hematocrit (Hct) is associated with an increased risk of pre-hypertension and all-cause death in general population, and people with a high Hct value are susceptible to arterial cardiovascular disease and venous thromboembolism. In this study, we report for the first time on the ability of thermoacoustic imaging (TAI) for in vivo evaluating Hct changes in human forearms. In vitro blood samples with different Hct values from healthy volunteers (n=3) were prepared after centrifugation. TAI was performed using these samples in comparison with the direct measurements of conductivity. In vivo TAI was conducted in the forearm of healthy volunteers (n=7) where Hct changes were produced through a vascular occlusion stimulation over a period of time. The results of in vitro blood samples obtained from the 3 healthy subjects show that the thermoacoustic (TA) signals changes due to the variation of blood conductivity are closely related to the changes in Hct. In addition, the in vivo TA signals obtained from the 7 healthy subjects consistently increase in the artery/muscle and decrease in the vein during venous or arterial occlusion because of the changed Hct value in their forearms. These findings suggest that TAI has the potential to become a new tool for monitoring Hct changes for a variety of pre-clinical and clinical applications.
 Effects of Prandtl number in two-dimensional turbulent convection Jian-Chao He(何建超), Ming-Wei Fang(方明卫), Zhen-Yuan Gao(高振源), Shi-Di Huang(黄仕迪), and Yun Bao(包芸) Chin. Phys. B, 2021, 30 (9):  094701.  DOI: 10.1088/1674-1056/ac0781 Abstract ( 48 )   HTML ( 1 )   PDF (7538KB) ( 13 )   We report a numerical study of the Prandtl-number (Pr) effects in two-dimensional turbulent Rayleigh-Bénard convection. The simulations were conducted in a square box over the Pr range from 0.25 to 100 and over the Rayleigh number (Ra) range from 107 to 1010. We find that both the strength and the stability of the large-scale flow decrease with the increasing of Pr, and the flow pattern becomes plume-dominated at high Pr. The evolution in flow pattern is quantified by the Reynolds number (Re), with the Ra and the Pr scaling exponents varying from 0.54 to 0.67 and -0.87 to -0.93, respectively. It is further found that the non-dimensional heat flux at small Ra diverges strongly for different Pr, but their difference becomes marginal as Ra increases. For the thermal boundary layer, the spatially averaged thicknesses for all the Pr numbers can be described by δθ～Ra-0.30 approximately, but the local values vary a lot for different Pr, which become more uniform with Pr increasing.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
 ISSDE: A Monte Carlo implicit simulation code based on Stratonovich SDE approach of Coulomb collision Yifeng Zheng(郑艺峰), Jianyuan Xiao(肖建元), Yanpeng Wang(王彦鹏), Jiangshan Zheng(郑江山), and Ge Zhuang(庄革) Chin. Phys. B, 2021, 30 (9):  095201.  DOI: 10.1088/1674-1056/abefc7 Abstract ( 70 )   HTML ( 0 )   PDF (3704KB) ( 129 )   A Monte Carlo implicit simulation program, Implicit Stratonovich Stochastic Differential Equations (ISSDE), is developed for solving stochastic differential equations (SDEs) that describe plasmas with Coulomb collision. The basic idea of the program is the stochastic equivalence between the Fokker-Planck equation and the Stratonovich SDEs. The splitting method is used to increase the numerical stability of the algorithm for dynamics of charged particles with Coulomb collision. The cases of Lorentzian plasma, Maxwellian plasma and arbitrary distribution function of background plasma have been considered. The adoption of the implicit midpoint method guarantees exactly the energy conservation for the diffusion term and thus improves the numerical stability compared with conventional Runge-Kutta methods. ISSDE is built with C++ and has standard interfaces and extensible modules. The slowing down processes of electron beams in unmagnetized plasma and relaxation process in magnetized plasma are studied using the ISSDE, which shows its correctness and reliability.
 Unstable mode of ion-acoustic waves with two temperature q-nonextensive distributed electrons S Bukhari, Nadeem Hussain, and S Ali Chin. Phys. B, 2021, 30 (9):  095202.  DOI: 10.1088/1674-1056/abf641 Abstract ( 46 )   HTML ( 0 )   PDF (1537KB) ( 20 )   The linear characteristics of the unstable mode of ion-acoustic waves are examined in an electrostatic electron-ion plasma composed of streaming hot electrons, non-streaming cold electrons and dynamical positive ions. The plasma under consideration is modeled by using a non-gyrotropic nonextensive q-distribution function in which the free energy source for wave excitation is provided by the relative directed motion of streaming hot electrons with respect to the other plasma species. In the frame work of kinetic model, a linearized set of Vlasov-Poisson's equations are solved to obtain the analytical expressions for dispersion relation and Landau damping rate. The threshold condition for the unstable ion-acoustic wave is derived to assess the stability of the wave in the presence of nonextensive effects. Growth in the wave spectrum and nontrivial effects of q-nonextensive parameter on the ion-acoustic waves can be of interest for the readers in the regions of Saturns's magnetosphere.
 Plasma characteristics and broadband electromagnetic wave absorption in argon and helium capacitively coupled plasma Wen-Chong Ouyang(欧阳文冲), Qi Liu(刘琦), Tao Jin(金涛), and Zheng-Wei Wu(吴征威) Chin. Phys. B, 2021, 30 (9):  095203.  DOI: 10.1088/1674-1056/abeb0d Abstract ( 60 )   HTML ( 0 )   PDF (1032KB) ( 27 )   A one-dimensional self-consistent calculation model of capacitively coupled plasma (CCP) discharge and electromagnetic wave propagation is developed to solve the plasma characteristics and electromagnetic wave transmission attenuation. Numerical simulation results show that the peak electron number density of argon is about 12 times higher than that of helium, and that the electron number density increases with the augment of pressure, radio frequency (RF) power, and RF frequency. However, the electron number density first increases and then decreases as the discharge gap increases. The transmission attenuation of electromagnetic wave in argon discharge plasma is 8.5-dB higher than that of helium. At the same time, the transmission attenuation increases with the augment of the RF power and RF frequency, but it does not increase or decrease monotonically with the increase of gas pressure and discharge gap. The electromagnetic wave absorption frequency band of the argon discharge plasma under the optimal parameters in this paper can reach the Ku band. It is concluded that the argon CCP discharge under the optimal discharge parameters has great potential applications in plasma stealth.
 Discharge characteristic of very high frequency capacitively coupled argon plasma Gui-Qin Yin(殷桂琴), Jing-Jing Wang(王兢婧), Shan-Shan Gao(高闪闪), Yong-Bo Jiang(姜永博), and Qiang-Hua Yuan(袁强华) Chin. Phys. B, 2021, 30 (9):  095204.  DOI: 10.1088/1674-1056/abf104 Abstract ( 33 )   HTML ( 0 )   PDF (1029KB) ( 11 )   The discharge characteristics of capacitively coupled argon plasmas driven by very high frequency discharge are studied. The mean electron temperature and electron density are calculated by using the Ar spectral lines at different values of power (20 W-70 W) and four different frequencies (13.56 MHz, 40.68 MHz, 94.92 MHz, and 100 MHz). The mean electron temperature decreases with the increase of power at a fixed frequency. The mean electron temperature varies non-linearly with frequency increasing at constant power. At 40.68 MHz, the mean electron temperature is the largest. The electron density increases with the increase of power at a fixed frequency. In the cases of driving frequencies of 94.92 MHz and 100 MHz, the obtained electron temperatures are almost the same, so are the electron densities. Particle-in-cell/Monte-Carlo collision (PIC/MCC) method developed within the Vsim 8.0 simulation package is used to simulate the electron density, the potential distribution, and the electron energy probability function (EEPF) under the experimental condition. The sheath width increases with the power increasing. The EEPF of 13.56 MHz and 40.68 MHz are both bi-Maxwellian with a large population of low-energy electrons. The EEPF of 94.92 MHz and 100 MHz are almost the same and both are nearly Maxwellian.
 Numerical investigation of radio-frequency negative hydrogen ion sources by a three-dimensional fluid model Ying-Jie Wang(王英杰), Jia-Wei Huang(黄佳伟), Quan-Zhi Zhang(张权治), Yu-Ru Zhang(张钰如), Fei Gao(高飞), and You-Nian Wang(王友年) Chin. Phys. B, 2021, 30 (9):  095205.  DOI: 10.1088/1674-1056/ac0e21 Abstract ( 82 )   HTML ( 1 )   PDF (1778KB) ( 61 )   A three-dimensional fluid model is developed to investigate the radio-frequency inductively coupled H2 plasma in a reactor with a rectangular expansion chamber and a cylindrical driver chamber, for neutral beam injection system in CFETR. In this model, the electron effective collision frequency and the ion mobility at high E-fields are employed, for accurate simulation of discharges at low pressures (0.3 Pa-2 Pa) and high powers (40 kW-100 kW). The results indicate that when the high E-field ion mobility is taken into account, the electron density is about four times higher than the value in the low E-field case. In addition, the influences of the magnetic field, pressure and power on the electron density and electron temperature are demonstrated. It is found that the electron density and electron temperature in the xz-plane along permanent magnet side become much more asymmetric when magnetic field enhances. However, the plasma parameters in the yz-plane without permanent magnet side are symmetric no matter the magnetic field is applied or not. Besides, the maximum of the electron density first increases and then decreases with magnetic field, while the electron temperature at the bottom of the expansion region first decreases and then almost keeps constant. As the pressure increases from 0.3 Pa to 2 Pa, the electron density becomes higher, with the maximum moving upwards to the driver region, and the symmetry of the electron temperature in the xz-plane becomes much better. As power increases, the electron density rises, whereas the spatial distribution is similar. It can be summarized that the magnetic field and gas pressure have great influence on the symmetry of the plasma parameters, while the power only has little effect.
 Numerical simulation of anode heat transfer of nitrogen arc utilizing two-temperature chemical non-equilibrium model Chong Niu(牛冲), Surong Sun(孙素蓉), Jianghong Sun(孙江宏), and Haixing Wang(王海兴) Chin. Phys. B, 2021, 30 (9):  095206.  DOI: 10.1088/1674-1056/ac133a Abstract ( 74 )   HTML ( 0 )   PDF (2218KB) ( 42 )   A detailed understanding of anode heat transfer is important for the optimization of arc processing technology. In this paper, a two-temperature chemical non-equilibrium model considering the collisionless space charge sheath is developed to investigate the anode heat transfer of nitrogen free-burning arc. The temperature, total heat flux and different heat flux components are analyzed in detail under different arc currents and anode materials. It is found that the arc current can affect the parameter distributions of anode region by changing plasma characteristics in arc column. As the arc current increases from 100 A to 200 A, the total anode heat flux increases, however, the maximum electron condensation heat flux decreases due to the arc expansion. The anode materials have a significant effect on the temperature and heat flux distributions in the anode region. The total heat flux on thoriated tungsten anode is lower than that on copper anode, while the maximum temperature is higher. The power transferred to thoriated tungsten anode, ranked in descending order, is heat flux from heavy-species, electron condensation heat, heat flux from electrons and ion recombination heat. However, the electron condensation heat makes the largest contribution for power transferred to copper anode.
 Micro-pinch formation and extreme ultraviolet emission of laser-induced discharge plasma Jun-Wu Wang(王均武), Xin-Bing Wang(王新兵), Du-Luo Zuo(左都罗), and Vassily S. Zakharov Chin. Phys. B, 2021, 30 (9):  095207.  DOI: 10.1088/1674-1056/ac078f Abstract ( 31 )   HTML ( 0 )   PDF (1533KB) ( 13 )   Extreme ultraviolet (EUV) source produced by laser-induced discharge plasma (LDP) is a potential technical means in inspection and metrology. A pulsed Nd:YAG laser is focused on a tin plate to produce an initial plasma thereby triggering a discharge between high-voltage electrodes in a vacuum system. The process of micro-pinch formation during the current rising is recorded by a time-resolved intensified charge couple device camera. The evolution of electron temperature and density of LDP are obtained by optical emission spectrometry. An extreme ultraviolet spectrometer is built up to investigate the EUV spectrum of Sn LDP at 13.5 nm. The laser and discharge parameters such as laser energy, voltage, gap distance, and anode shape can influence the EUV emission.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
 Stability of liquid crystal systems doped with γ-Fe2O3 nanoparticles Xu Zhang(张旭), Ningning Liu(刘宁宁), Zongyuan Tang(唐宗元), Yingning Miao(缪应宁), Xiangshen Meng(孟祥申), Zhenghong He(何正红), Jian Li(李建), Minglei Cai(蔡明雷), Tongzhou Zhao(赵桐州), Changyong Yang(杨长勇), Hongyu Xing(邢红玉), and Wenjiang Ye(叶文江) Chin. Phys. B, 2021, 30 (9):  096101.  DOI: 10.1088/1674-1056/abeb11 Abstract ( 47 )   HTML ( 0 )   PDF (2795KB) ( 13 )   In order to explore the stability of a liquid crystal (LC) system doped with γ-Fe2O3 nanoparticles, the physical properties (clearing point, dielectric properties), electro-optical properties and residual direct-current voltage (RDCV) of the doped LC system were measured and evaluated at different times. First, the temperature was controlled by precision hot stage, and the clearing point temperature of doped LC was observed and measured by a polarized optical microscope. Using a precision LCR meter, we measured the capacitance-voltage curves of the doped LC system at the temperature of 27 ℃. The dielectric constant of doped LC was calculated by the dualcell capacitance method. Then, the electro-optical properties of the doped LC system were measured. Finally, the RDCV of the doped LC system was measured and calculated. After five months, the parameters of the doped LC system were re-measured and analyzed under the same conditions to evaluate its stability. The experimental results show that, within five months, the clearing point change rate of doped LC is in the range of 0.24%-1.37%, the change of dielectric anisotropy is in the range of 0.035-0.2, the curves of electro-optical properties are basically fitted, and the change rate of saturated RDCV is about 11.2%, which basically indicate that the LC system doped with γ-Fe2O3 nanoparticles has good stability.
 Structural, magnetic, and dielectric properties of Ni-Zn ferrite and Bi2O3 nanocomposites prepared by the sol-gel method Jinmiao Han(韩晋苗), Li Sun(孙礼), Ensi Cao(曹恩思), Wentao Hao(郝文涛), Yongjia Zhang(张雍家), and Lin Ju(鞠林) Chin. Phys. B, 2021, 30 (9):  096102.  DOI: 10.1088/1674-1056/ac0904 Abstract ( 44 )   HTML ( 0 )   PDF (3036KB) ( 15 )   Ni-Zn ferrite and Bi2O3 composites were developed by the sol-gel method. The structural, magnetic, and dielectric properties were studied for all the prepared samples. X-ray diffraction (XRD) was performed to study the crystal structure. The results of field emission scanning electron microscopy (FE-SEM) showed that the addition of Bi2O3 can increase the grain size of the Ni-Zn ferrite. Magnetic properties were analyzed by a hysteresis loop test and it was found that the saturation magnetization and coercivity decreased with the increase of Bi2O3 ratio. In addition, the dielectric properties of the Ni-Zn ferrite were also improved with the addition of Bi2O3.
 Highly tunable plasmon-induced transparency with Dirac semimetal metamaterials Chunzhen Fan(范春珍), Peiwen Ren(任佩雯), Yuanlin Jia(贾渊琳), Shuangmei Zhu(朱双美), and Junqiao Wang(王俊俏) Chin. Phys. B, 2021, 30 (9):  096103.  DOI: 10.1088/1674-1056/abf4bf Abstract ( 55 )   HTML ( 0 )   PDF (1809KB) ( 28 )   Based on Dirac semimetal metamaterials, the tunable plasmon induced transparency (PIT) is investigated elaborately in this work. The designed unit cell consists of a strip and a square bracket, which is periodically aligned on the dielectric substrate. Our numerical results illustrate that a pronounced transparency window exists due to near field coupling between two bright modes, which can be dynamically tuned with Fermi energy. Namely, the transparency window demonstrates a distinct blue shift with a larger Fermi energy. Moreover, an on-to-off switch of the PIT transparency window is realized with different polarization angles. In addition, the accompanied slow light property is examined with the calculation of phase and group delay. Finally, a small variation of the refractive index of the substrate can induce a clear movement of the PIT transparency window which delivers a guidance in the application of optical sensing. Thus, this work provides us a new strategy to design compact and adjustable PIT devices and has potential applications in highly tunable optical switchers, sensors, and slow light devices.
 Sphere-shaped SiGe micro/nanostructures with tunable Ge composition and size formed by laser irradiation Xinxin Li(李欣欣), Zhen Deng(邓震), Sen Wang(王森), Jinbiao Liu(刘金彪), Jun Li(李俊), Yang Jiang(江洋), Ziguang Ma(马紫光), Chunhua Du(杜春花), Haiqiang Jia(贾海强), Wenxin Wang(王文新), and Hong Chen(陈弘) Chin. Phys. B, 2021, 30 (9):  096104.  DOI: 10.1088/1674-1056/ac0347 Abstract ( 43 )   HTML ( 0 )   PDF (1887KB) ( 32 )   SiGe spheres with different diameters are successfully fabricated on a virtual SiGe template using a laser irradiation method. The results from scanning electron microscopy and micro-Raman spectroscopy reveal that the diameter and Ge composition of the SiGe spheres can be well controlled by adjusting the laser energy density. In addition, the transmission electron microscopy results show that Ge composition inside the SiGe spheres is almost uniform in a well-defined, nearly spherical outline. As a convenient method to prepare sphere-shaped SiGe micro/nanostructures with tunable Ge composition and size, this technique is expected to be useful for SiGe-based material growth and micro/optoelectronic device fabrication.
 Strain-tuned magnetic properties in (Ga,Fe)Sb: First-principles study Feng-Chun Pan(潘凤春), Xue-Ling Lin(林雪玲), and Xu-Ming Wang(王旭明) Chin. Phys. B, 2021, 30 (9):  096105.  DOI: 10.1088/1674-1056/ac00a2 Abstract ( 53 )   HTML ( 0 )   PDF (2801KB) ( 26 )   In view of the importance of enhancing ferromagnetic (FM) coupling in dilute magnetic semiconductors (DMSs), the effects of strain on the electronic structures and magnetic properties of (Ga,Fe)Sb were examined by a first-principles study. The results of the investigation indicate that Fem Ga substitution takes place in the low-spin state (LSS) with a total magnetic moment of 1μB in the strain range of -3% to 0.5%, which transitions to the high-spin state (HSS) with a total magnetic moment of 5μB as the strain changes from 0.6% to 3%. We attribute the changes in the amount and distribution of the total moment to the influence of the crystal field under different strains. The FM coupling is strongest under a strain of about 0.5%, but gradually becomes weaker with increasing compressive and tensile strains. The magnetic coupling mechanism is discussed in detail. Our results highlight the important contribution of strain to magnetic moment and FM interaction intensity, and present an interesting avenue for the future design of high Curie temperature (TC) materials in the (Ga,Fe)Sb system.
 Nanoscale structural investigation of Zn1-xMgxO alloy films on polar and nonpolar ZnO substrates with different Mg contents Xin Liang(梁信), Hua Zhou(周华), Hui-Qiong Wang(王惠琼), Lihua Zhang(张丽华), Kim Kisslinger, and Junyong Kang(康俊勇) Chin. Phys. B, 2021, 30 (9):  096107.  DOI: 10.1088/1674-1056/ac11e1 Abstract ( 64 )   HTML ( 0 )   PDF (5625KB) ( 31 )   Zn1-xMgxO alloy films are important deep ultraviolet photoelectric materials. In this work, we used plasma-assisted molecular beam epitaxy to prepare Zn1-xMgxO films with different magnesium contents on polar (0001) and nonpolar (1010) ZnO substrates. The nanoscale structural features of the grown alloy films as well as the interfaces were investigated. It was observed that the cubic phases of the alloy films emerged when the Mg content reached 20% and 37% for the alloy films grown on the (0001) and (1010) ZnO substrates, respectively. High-resolution transmission electron microscopy images revealed cubic phases without visible hexagonal phases for the alloy films with more than 70% magnesium, and the cubic phases exhibited three-fold and two-fold rotations for the alloy films on the polar (0001) and nonpolar (1010) ZnO substrates, respectively. This work aims to provide references for monitoring the Zn1-xMgxO film structure with respect to different substrate orientations.
 Molecular dynamics study of coupled layer thickness and strain rate effect on tensile behaviors of Ti/Ni multilayered nanowires Meng-Jia Su(宿梦嘉), Qiong Deng(邓琼), Lan-Ting Liu(刘兰亭), Lian-Yang Chen(陈连阳), Meng-Long Su(宿梦龙), and Min-Rong An(安敏荣) Chin. Phys. B, 2021, 30 (9):  096201.  DOI: 10.1088/1674-1056/abf10a Abstract ( 39 )   HTML ( 0 )   PDF (4949KB) ( 16 )   Novel properties and applications of multilayered nanowires (MNWs) urge researchers to understand their mechanical behaviors comprehensively. Using the molecular dynamic simulation, tensile behaviors of Ti/Ni MNWs are investigated under a series of layer thickness values (1.31, 2.34, and 7.17 nm) and strain rates (1.0×108 s-1≤$\dot \varepsilon$≤ 5.0×1010 s-1). The results demonstrate that deformation mechanisms of isopachous Ti/Ni MNWs are determined by the layer thickness and strain rate. Four distinct strain rate regions in the tensile process can be discovered, which are small, intermediate, critical, and large strain rate regions. As the strain rate increases, the initial plastic behaviors transform from interface shear (the shortest sample) and grain reorientation (the longest sample) in small strain rate region to amorphization of crystalline structures (all samples) in large strain rate region. Microstructure evolutions reveal that the disparate tensile behaviors are ascribed to the atomic fractions of different structures in small strain rate region, and only related to collapse of crystalline atoms in high strain rate region. A layer thickness-strain rate-dependent mechanism diagram is given to illustrate the couple effect on the plastic deformation mechanisms of the isopachous nanowires. The results also indicate that the modulation ratio significantly affects the tensile properties of unequal Ti/Ni MNWs, but barely affect the plastic deformation mechanisms of the materials. The observations from this work will promote theoretical researches and practical applications of Ti/Ni MNWs.
 An improved model of damage depth of shock-melted metal in microspall under triangular wave loading Wen-Bin Liu(刘文斌), An-Min He(何安民), Kun Wang(王昆), Jian-Ting Xin(辛建婷), Jian-Li Shao(邵建立), Nan-Sheng Liu(刘难生), and Pei Wang(王裴) Chin. Phys. B, 2021, 30 (9):  096202.  DOI: 10.1088/1674-1056/abeb10 Abstract ( 39 )   HTML ( 0 )   PDF (1109KB) ( 18 )   Damage depth is an important dynamic parameter for describing the degree of material damage and is also a key fundamental issue in the field of impact compression technology. The present work is dedicated to the damage depth of shock-melted metal in microspall under triangular wave loading, and an improved model of damage depth considering the material's compressibility and relative movement is proposed. The damage depth obtained from the proposed model is in good agreement with the laser-driven shock loading experiment. Compared with the previous model, the proposed model can predict the damage depth of shock-melted metal in microspall more accurately. Furthermore, two-groups of the smoothed particle hydrodynamics (SPH) simulations are carried out to investigate the effects of peak stress and decay length of the incident triangular wave on the damage depth, respectively. As the decay length increases, the damage depth increases linearly. As the peak stress increases, the damage depth increases nonlinearly, and the increase in damage depth gradually slows down. The results of the SPH simulations adequately reproduce the results of the proposed model in terms of the damage depth. Finally, it is found that the threshold stress criterion can reflect the macroscopic characteristics of microspall of melted metal.
 Probing thermal properties of vanadium dioxide thin films by time-domain thermoreflectance without metal film Qing-Jian Lu(陆青鑑), Min Gao(高敏), Chang Lu(路畅), Fei Long(龙飞), Tai-Song Pan(潘泰松), and Yuan Lin(林媛) Chin. Phys. B, 2021, 30 (9):  096801.  DOI: 10.1088/1674-1056/abea94 Abstract ( 38 )   HTML ( 1 )   PDF (781KB) ( 11 )   Vanadium dioxide (VO2) is a strongly correlated material, and it has become known due to its sharp metal-insulator transition (MIT) near room temperature. Understanding the thermal properties and their change across MIT of VO2 thin film is important for the applications of this material in various devices. Here, the changes in thermal conductivity of epitaxial and polycrystalline VO2 thin film across MIT are probed by the time-domain thermoreflectance (TDTR) method. The measurements are performed in a direct way devoid of deposition of any metal thermoreflectance layer on the VO2 film to attenuate the impact from extra thermal interfaces. It is demonstrated that the method is feasible for the VO2 films with thickness values larger than 100 nm and beyond the phase transition region. The observed reasonable thermal conductivity change rates across MIT of VO2 thin films with different crystal qualities are found to be correlated with the electrical conductivity change rate, which is different from the reported behavior of single crystal VO2 nanowires. The recovery of the relationship between thermal conductivity and electrical conductivity in VO2 film may be attributed to the increasing elastic electron scattering weight, caused by the defects in the film. This work demonstrates the possibility and limitation of investigating the thermal properties of VO2 thin films by the TDTR method without depositing any metal thermoreflectance layer.
 C9N4 as excellent dual electrocatalyst: A first principles study Wei Xu(许伟), WenWu Xu(许文武), and Xiangmei Duan(段香梅) Chin. Phys. B, 2021, 30 (9):  096802.  DOI: 10.1088/1674-1056/ac0ccf Abstract ( 58 )   HTML ( 0 )   PDF (1022KB) ( 60 )   We perform first principles calculations to investigate the catalytic behavior of C9N4 nanosheet for water splitting. For the pristine C9N4, we find that, at different hydrogen coverages, two H atoms adsorbed on the 12-membered ring and one H atom adsorbed on the 9-membered ring show excellent performance of hydrogen evolution reaction (HER). Tensile strain could improve the catalytic ability of C9N4 and strain can be practically introduced by building C9N4/BiN, and C9N4/GaAs heterojunctions. We demonstrate that the HER performance of heterojunctions is indeed improved compared with that of C9N4 nanosheet. Anchoring transition metal atoms on C9N4 is another strategy to apply strain. It shows that Rh@C9N4 exhibits superior HER property with very low Gibbs free energy change of -30 meV. Under tensile strain within ～2%, Rh@C9N4 could catalyze HER readily. Moreover, the catalyst Rh@C9N4 works well for oxygen evolution reaction (OER) with an overpotential of 0.58 V. Our results suggest that Rh@C9N4 is favorable for both HER and OER because of its metallic conductivity, close-zero Gibbs free energy change, and low oneset overpotential. The outstanding performance of C9N4 nanosheet could be attributed to the tunable porous structure and electronic structure compatibility.
 Ohmic and Schottky contacts of hydrogenated and oxygenated boron-doped single-crystal diamond with hill-like polycrystalline grains Jing-Cheng Wang(王旌丞), Hao Chen(陈浩), Lin-Feng Wan(万琳丰), Cao-Yuan Mu(牟草源), Yao-Feng Liu(刘尧峰), Shao-Heng Cheng(成绍恒), Qi-Liang Wang(王启亮), Liu-An Li(李柳暗), and Hong-Dong Li(李红东) Chin. Phys. B, 2021, 30 (9):  096803.  DOI: 10.1088/1674-1056/ac032b Abstract ( 58 )   HTML ( 0 )   PDF (1390KB) ( 26 )   Hill-like polycrystalline diamond grains (HPDGs) randomly emerged on a heavy boron-doped p+ single-crystal diamond (SCD) film by prolonging the growth duration of the chemical vapor deposition process. The Raman spectral results confirm that a relatively higher boron concentration (～ 1.1×1021 cm-3) is detected on the HPDG with respect to the SCD region (～ 5.4×1020 cm-3). It demonstrates that the Au/SCD interface can be modulated from ohmic to Schottky contact by varying the surface from hydrogen to oxygen termination. The current-voltage curve between two HPDGs is nearly linear with either oxygen or hydrogen termination, which means that the HPDGs provide a leakage path to form an ohmic contact. There are obvious rectification characteristics between oxygen-terminated HPDGs and SCD based on the difference in boron doping levels in those regions. The results reveal that the highly boron-doped HPDGs grown in SCD can be adopted as ohmic electrodes for Hall measurement and electronic devices.
 Phase transition-induced superstructures of β-Sn films with atomic-scale thickness Le Lei(雷乐), Feiyue Cao(曹飞跃), Shuya Xing(邢淑雅), Haoyu Dong(董皓宇), Jianfeng Guo(郭剑锋), Shangzhi Gu(顾尚志), Yanyan Geng(耿燕燕), Shuo Mi(米烁), Hanxiang Wu(吴翰翔), Fei Pang(庞斐), Rui Xu(许瑞), Wei Ji(季威), and Zhihai Cheng(程志海) Chin. Phys. B, 2021, 30 (9):  096804.  DOI: 10.1088/1674-1056/ac11e8 Abstract ( 62 )   HTML ( 0 )   PDF (1842KB) ( 42 )   The ultrathin β-Sn(001) films have attracted tremendous attention owing to its topological superconductivity (TSC), which hosts Majorana bound state (MBSs) for quantum computation. Recently, β-Sn(001) thin films have been successfully fabricated via phase transition engineering. However, the understanding of structural phase transition of β-Sn(001) thin films is still elusive. Here, we report the direct growth of ultrathin β-Sn(001) films epitaxially on the highly oriented pyrolytic graphite (HOPG) substrate and the characterization of intricate structural-transition-induced superstructures. The morphology was obtained by using atomic force microscopy (AFM) and low-temperature scanning tunneling microscopy (STM), indicating a structure-related bilayer-by-bilayer growth mode. The ultrathin β-Sn film was made of multiple domains with various superstructures. Both high-symmetric and distorted superstructures were observed in the atomic-resolution STM images of these domains. The formation mechanism of these superstructures was further discussed based on the structural phase transition of β to α-Sn at the atomic-scale thickness. Our work not only brings a deep understanding of the structural phase transition of Sn film at the two-dimensional limit, but also paves a way to investigate their structure-sensitive topological properties.
 Adsorption and rotational barrier for a single azobenzene molecule on Au(111) surface Dong Hao(郝东), Xiangqian Tang(唐向前), Wenyu Wang(王文宇), Yang An(安旸), Yueyi Wang(王悦毅), Xinyan Shan(单欣岩), and Xinghua Lu(陆兴华) Chin. Phys. B, 2021, 30 (9):  096805.  DOI: 10.1088/1674-1056/ac11d9 Abstract ( 75 )   HTML ( 0 )   PDF (1100KB) ( 38 )   The orientation switching of a single azobenzene molecule on Au(111) surface excited by tunneling electrons and/or photons has been demonstrated in recent experiments. Here we investigate the rotation behavior of this molecular rotor by first-principles density functional theory (DFT) calculation. The anchor phenyl ring prefers adsorption on top of the fcc hollow site, simulated by a benzene molecule on close packed atomic surface. The adsorption energy for an azobenzene molecule on Au(111) surface is calculated to be about 1.76 eV. The rotational energy profile has been mapped with one of the phenyl rings pivots around the fcc hollow site, illustrating a potential barrier about 50 meV. The results are consistent with experimental observations and valuable for exploring a broad spectrum of molecules on this noble metal surface.
 Atomic and electronic structures of p-type dopants in 4H-SiC Lingyan Lu(卢玲燕), Han Zhang(张涵), Xiaowei Wu(吴晓维), Jing Shi(石晶), and Yi-Yang Sun(孙宜阳) Chin. Phys. B, 2021, 30 (9):  096806.  DOI: 10.1088/1674-1056/ac1e22 Abstract ( 79 )   HTML ( 0 )   PDF (1294KB) ( 113 )   Using hybrid density functional calculation, we study the atomic and electronic structures of p-type dopants, B, Al and Ga, in 4H-SiC. For B, depending on the growth condition, it can occupy both Si and C sites. In contrast, Al and Ga on the C sites exhibit too high formation energy to exist in a significant amount. In 4H-SiC, there exist two types of Si sites in wurtzite-like and zincblende-like local coordination, respectively. Our calculations suggest that the dopant atoms have negligible preference occupying the two sites. In neutral charge state, all the dopants exhibit significant distortions from the structure in the negatively charged state. For most cases, our calculations yield three distorted structures, in which the most stable one has the dopant atom displaced along its bond with one of the surrounding equatorial Si or C atoms, lowering the C3v symmetry to Cs symmetry (i.e., a mirror symmetry only). Among the three dopant elements, Al on Si sites exhibits overall the lowest formation energy and the shallowest acceptor level. Nevertheless, it is not a hydrogenic dopant with the acceptor level 0.12 eV above the valence band maximum based on calculation using a 400-atom supercell. Its corresponding defect state exhibits apparent localization along the [0001] direction, but it is relatively delocalized in the (0001) plane.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
 Fang-Howard wave function modelling of electron mobility in AlInGaN/AlN/InGaN/GaN double heterostructures Yao Li(李姚) and Hong-Bin Pu(蒲红斌) Chin. Phys. B, 2021, 30 (9):  097201.  DOI: 10.1088/1674-1056/abea87 Abstract ( 54 )   HTML ( 0 )   PDF (2173KB) ( 12 )   To study the electron transport properties in InGaN channel-based heterostructures, a revised Fang-Howard wave function is proposed by combining the effect of GaN back barrier. Various scattering mechanisms, such as dislocation impurity (DIS) scattering, polar optical phonon (POP) scattering, piezoelectric field (PE) scattering, interface roughness (IFR) scattering, deformation potential (DP) scattering, alloy disorder (ADO) scattering from InGaN channel layer, and temperature-dependent energy bandgaps are considered in the calculation model. A contrast of AlInGaN/AlN/InGaN/GaN double heterostructure (DH) to the theoretical AlInGaN/AlN/InGaN single heterostructure (SH) is made and analyzed with a full range of barrier alloy composition. The effect of channel alloy composition on InGaN channel-based DH with technologically important Al(In,Ga)N barrier is estimated and optimal indium mole fraction is 0.04 for higher mobility in DH with Al0.4In0.07Ga0.53N barrier. Finally, the temperature-dependent two-dimensional electron gas (2DEG) density and mobility in InGaN channel-based DH with Al0.83In0.13Ga0.04N and Al0.4In0.07Ga0.53N barrier are investigated. Our results are expected to conduce to the practical application of InGaN channel-based heterostructures.
 Mobility edges and reentrant localization in one-dimensional dimerized non-Hermitian quasiperiodic lattice Xiang-Ping Jiang(蒋相平), Yi Qiao(乔艺), and Jun-Peng Cao(曹俊鹏) Chin. Phys. B, 2021, 30 (9):  097202.  DOI: 10.1088/1674-1056/ac11e5 Abstract ( 73 )   HTML ( 0 )   PDF (10206KB) ( 50 )   The mobility edges and reentrant localization transitions are studied in one-dimensional dimerized lattice with non-Hermitian either uniform or staggered quasiperiodic potentials. We find that the non-Hermitian uniform quasiperiodic disorder can induce an intermediate phase where the extended states coexist with the localized ones, which implies that the system has mobility edges. The localization transition is accompanied by the $\mathcal{PT}$ symmetry breaking transition. While if the non-Hermitian quasiperiodic disorder is staggered, we demonstrate the existence of multiple intermediate phases and multiple reentrant localization transitions based on the finite size scaling analysis. Interestingly, some already localized states will become extended states and can also be localized again for certain non-Hermitian parameters. The reentrant localization transitions are associated with the intermediate phases hosting mobility edges. Besides, we also find that the non-Hermiticity can break the reentrant localization transition where only one intermediate phase survives. More detailed information about the mobility edges and reentrant localization transitions are presented by analyzing the eigenenergy spectrum, inverse participation ratio, and normalized participation ratio.
 Strain-dependent resistance and giant gauge factor in monolayer WSe2 Hot! Mao-Sen Qin(秦茂森), Xing-Guo Ye(叶兴国), Peng-Fei Zhu(朱鹏飞), Wen-Zheng Xu(徐文正), Jing Liang(梁晶), Kaihui Liu(刘开辉), and Zhi-Min Liao(廖志敏) Chin. Phys. B, 2021, 30 (9):  097203.  DOI: 10.1088/1674-1056/ac11d2 Abstract ( 179 )   HTML ( 1 )   PDF (949KB) ( 186 )   We report the strong dependence of resistance on uniaxial strain in monolayer WSe2 at various temperatures, where the gauge factor can reach as large as 2400. The observation of strain-dependent resistance and giant gauge factor is attributed to the emergence of nonzero Berry curvature dipole. Upon increasing strain, Berry curvature dipole can generate net orbital magnetization, which would introduce additional magnetic scattering, decreasing the mobility and thus conductivity. Our work demonstrates the strain engineering of Berry curvature and thus the transport properties, making monolayer WSe2 potential for application in the highly sensitive strain sensors and high-performance flexible electronics.
 Thermoelectric enhancement in triple-doped strontium titanate with multi-scale microstructure Zheng Cao(曹正), Qing-Qiao Fu(傅晴俏), Hui Gu(顾辉), Zhen Tian(田震), Xinba Yaer(新巴雅尔), Juan-Juan Xing(邢娟娟), Lei Miao(苗蕾), Xiao-Huan Wang(王晓欢), Hui-Min Liu(刘慧敏), and Jun Wang(王俊) Chin. Phys. B, 2021, 30 (9):  097204.  DOI: 10.1088/1674-1056/abe9a9 Abstract ( 38 )   HTML ( 0 )   PDF (5973KB) ( 24 )   Strontium titanate (SrTiO3) is a thermoelectric material with large Seebeck coefficient that has potential applications in high-temperature power generators. To simultaneously achieve a low thermal conductivity and high electrical conductivity, polycrystalline SrTiO3 with a multi-scale architecture was designed by the co-doping with lanthanum, cerium, and niobium. High-quality nano-powders were synthesized via a hydrothermal method. Nano-inclusions and a nano/micro-sized second phase precipitated during sintering to form mosaic crystal-like and epitaxial-like structures, which decreased the thermal conductivity. Substituting trivalent Ce and/or La with divalent Sr and substituting pentavalent Nb with tetravalent Ti enhanced the electrical conductivity without decreasing the Seebeck coefficient. By optimizing the dopant type and ratio, a low thermal conductivity of 2.77 W·m-1·K-1 and high PF of 1.1 mW·m-1·K-2 at 1000 K were obtained in the sample co-doped with 5-mol% La, 5-mol% Ce, and 5-mol% Nb, which induced a large ZT of 0.38 at 1000 K.
 First-principles study of plasmons in doped graphene nanostructures Xiao-Qin Shu(舒晓琴), Xin-Lu Cheng(程新路), Tong Liu(刘彤), and Hong Zhang(张红) Chin. Phys. B, 2021, 30 (9):  097301.  DOI: 10.1088/1674-1056/abe92d Abstract ( 63 )   HTML ( 0 )   PDF (1493KB) ( 31 )   The operating frequencies of surface plasmons in pristine graphene lie in the terahertz and infrared spectral range, which limits their utilization. Here, the high-frequency plasmons in doped graphene nanostructures are studied by the time-dependent density functional theory. The doping atoms include boron, nitrogen, aluminum, silicon, phosphorus, and sulfur atoms. The influences of the position and concentration of nitrogen dopants on the collective stimulation are investigated, and the effects of different types of doping atoms on the plasmonic stimulation are discussed. For different positions of nitrogen dopants, it is found that a higher degree of symmetry destruction is correlated with weaker optical absorption. In contrast, a higher concentration of nitrogen dopants is not correlated with a stronger absorption. Regarding different doping atoms, atoms similar to carbon atom in size, such as boron atom and nitrogen atom, result in less spectral attenuation. In systems with other doping atoms, the absorption is significantly weakened compared with the absorption of the pristine graphene nanostructure. Plasmon energy resonance dots of doped graphene lie in the visible and ultraviolet spectral range. The doped graphene nanostructure presents a promising material for nanoscaled plasmonic devices with effective absorption in the visible and ultraviolet range.
 Protection of isolated and active regions in AlGaN/GaN HEMTs using selective laser annealing Mingchen Hou(侯明辰), Gang Xie(谢刚), Qing Guo(郭清), and Kuang Sheng(盛况) Chin. Phys. B, 2021, 30 (9):  097302.  DOI: 10.1088/1674-1056/abf34c Abstract ( 34 )   HTML ( 0 )   PDF (1615KB) ( 20 )   AlGaN/GaN high-electron-mobility transistors with Au-free ohmic contacts are fabricated by selective laser annealing and conventional rapid thermal annealing. The current transport mechanism of ohmic contacts is investigated. High-temperature annealing can be avoided in the isolated region and the active region by selective laser annealing. The implanted isolation leakage current is maintained 10-6 mA/mm even at 1000 V after selective laser annealing. On the contrary, high-temperature annealing will cause obvious degradation of the isolation. The morphology of AlGaN surface is measured by atomic force microscope. No noticeable change of the AlGaN surface morphology after selective laser annealing, while the root-mean-square roughness value markedly increases after rapid thermal annealing. The smaller frequency dispersion of capacitance-voltage characteristics confirms the lower density of surface states after selective laser annealing. Thus, dynamic on-resistance is effectively suppressed.
 High-resolution angle-resolved photoemission study of large magnetoresistance topological semimetal CaAl4 Xu-Chuan Wu(吴徐传), Shen Xu(徐升), Jian-Feng Zhang(张建丰), Huan Ma(马欢), Kai Liu(刘凯), Tian-Long Xia(夏天龙), and Shan-Cai Wang(王善才) Chin. Phys. B, 2021, 30 (9):  097303.  DOI: 10.1088/1674-1056/ac0cd7 Abstract ( 60 )   HTML ( 0 )   PDF (7424KB) ( 56 )   Extremely large magnetoresistance (XMR) has been explored in many nonmagnetic topologically nontrivial/trivial semimetals, while it is experimentally ambiguous which mechanism should be responsible in a specific material due to the complex electronic structures. In this paper, the magnetoresistance origin of single crystal CaAl4 with C2/m structure at low temperature is investigated, exhibiting unsaturated magnetoresistance of ～ 3000% at 2.5 K and 14 T as the fingerprints of XMR materials. By the combination of ARPES and the first-principles calculations, we elaborate multiband features and anisotropic Fermi surfaces, which can explain the mismatch of isotropic two-band model. Although the structural phase transition from I4/mmm to C2/m has been recognized, the subtle impact on electronic structure is revealed by our ARPES measurements. Considering that both charge compensation and potential topologically nontrivial band structure exist in CaAl4, our findings report CaAl4 as a new reference material for exploring the XMR phenomena.
 Negative tunnel magnetoresistance in a quantum dot induced by interplay of a Majorana fermion and thermal-driven ferromagnetic leads Peng-Bin Niu(牛鹏斌), Bo-Xiang Cui(崔博翔), and Hong-Gang Luo(罗洪刚) Chin. Phys. B, 2021, 30 (9):  097401.  DOI: 10.1088/1674-1056/abf10b Abstract ( 75 )   HTML ( 0 )   PDF (562KB) ( 30 )   We investigate the spin-related currents and tunnel magnetoresistance through a quantum dot, which is side-coupled with a Majorana fermion zero mode and two thermal-driven ferromagnetic electrodes. It is found that the interplay of Majorana fermion and electrodes' spin polarization can induce a nonlinear thermal-bias spin current. This interplay also decreases the total magnitude of spin or charge current, in either parallel or antiparallel configuration. In addition, a thermal-driven negative tunnel magnetoresistance is found, which is an unique feature to characterize Majorana fermion. With large temperature difference, a step phenomenon is observed in gate tuned spin-up current. When the coupling between quantum dot and topological superconductor is strong enough, this step will evolve into a linear relation, revealing Majorana fermion's robustness.
 Barrier or easy-flow channel: The role of grain boundary acting on vortex motion in type-II superconductors Yu Liu(刘宇), Xiao-Fan Gou(苟晓凡), and Feng Xue(薛峰) Chin. Phys. B, 2021, 30 (9):  097402.  DOI: 10.1088/1674-1056/ac11ea Abstract ( 39 )   HTML ( 0 )   PDF (1339KB) ( 22 )   Grain boundaries (GBs), as extremely anisotropic pinning defects, have a strong impact on vortex motion in type-Ⅱ superconductors, and further on the macro level dominates the superconductivity for example the critical current density. Many previous studies indicated that mostly GB plays the role of a strong barrier for vortex motion, while an easy-flow channel just under some certain conditions. In order to thoroughly make clear of the questions of what is exactly the role of GB on vortex motion and how it works, in this article we developed a large scale molecular dynamic model and revealed the action of GB on vortex motion in type-Ⅱ superconductors. The most significant finding is that the role of GB on vortex motion can be changeable from a barrier to an easy-flow channel, and which is intrinsically determined by the competition effect correlated with its action on vortex between in the GB and no-GB regions. Such the competition effect essentially depends on the attributes of both the GB (described by the GB strength and angle θ) and no-GB pining regions (by the relative disorder strength αp/αv). Specifically, for a YBa2Cu3O7-x (YBCO) sample, to obtain a clear knowledge of vortex motion in GB region, we visualized the three typical trajectories of vortices during the three vortex movement stages. Further, in order to understand how GB results in the macro current-carrying property, corresponding to the current-voltage relation of the YBCO conductor, we obtained the average velocity vy of vortices varying with their driving force, which is nearly identical with the previous observations.
 Magnetic dynamics of two-dimensional itinerant ferromagnet Fe3GeTe2 Lijun Ni(倪丽君), Zhendong Chen(陈振东), Wei Li(李威), Xianyang Lu(陆显扬), Yu Yan(严羽), Longlong Zhang(张龙龙), Chunjie Yan(晏春杰), Yang Chen(陈阳), Yaoyu Gu(顾耀玉), Yao Li(黎遥), Rong Zhang(张荣), Ya Zhai(翟亚), Ronghua Liu(刘荣华), Yi Yang(杨燚), and Yongbing Xu(徐永兵) Chin. Phys. B, 2021, 30 (9):  097501.  DOI: 10.1088/1674-1056/ac0e25 Abstract ( 77 )   HTML ( 0 )   PDF (932KB) ( 68 )   Among the layered two-dimensional ferromagnetic materials (2D FMs), due to a relatively high TC, the van der Waals (vdW) Fe3GeTe2 (FGT) crystal is of great importance for investigating its distinct magnetic properties. Here, we have carried out static and dynamic magnetization measurements of the FGT crystal with a Curie temperature TC ≈ 204 K. The M-H hysteresis loops with in-plane and out-of-plane orientations show that FGT has a strong perpendicular magnetic anisotropy with the easy axis along its c-axis. Moreover, we have calculated the uniaxial magnetic anisotropy constant (K1) from the SQUID measurements. The dynamic magnetic properties of FGT have been probed by utilizing the high sensitivity electron-spin-resonance (ESR) spectrometer at cryogenic temperatures. Based on an approximation of single magnetic domain mode, the K1 and the effective damping constant (αeff) have also been determined from the out-of-plane angular dependence of ferromagnetic resonance (FMR) spectra obtained at the temperature range of 185 K to TC. We have found large magnetic damping with the effective damping constant αeff～ 0.58 along with a broad linewidth (ΔHpp> 1000 Oe at 9.48 GHz, H||c-axis). Our results provide useful dynamics information for the development of FGT-based spintronic devices.
 Current-dependent positive magnetoresistance inLa0.8Ba0.2MnO3 ultrathin films Guankai Lin(林冠凯), Haoru Wang(王昊儒), Xuhui Cai(蔡旭晖), Wei Tong(童伟), and Hong Zhu(朱弘) Chin. Phys. B, 2021, 30 (9):  097502.  DOI: 10.1088/1674-1056/ac012d Abstract ( 36 )   HTML ( 0 )   PDF (581KB) ( 7 )   We report an investigation into the magnetoresistance (MR) of La0.8Ba0.2MnO3 ultrathin films with various thicknesses. While the 13 nm-thick film shows the commonly reported negative magnetoresistive effect, the 6 nm- and 4 nm-thick films display unconventional positive magnetoresistive (PMR) behavior under certain conditions. As well as the dependence on the film's thickness, it has been found that the electrical resistivity and the PMR effect of the thinner films are very dependent on the test current. For example, the magnetoresistive ratio of the 4 nm-thick film changes from +46% to -37% when the current is increased from 10 nA to 100 nA under 15 kOe at 40 K. In addition, the two thinner films present opposite changes in electrical resistivity with respect to the test current, i.e., the electroresistive (ER) effect, at low temperatures. We discuss the complex magnetoresistive and ER behaviors by taking account of the weak contacts at grain boundaries between ferromagnetic metallic (FMM) grains. The PMR effect can be attributed to the breaking of the weak contacts due to the giant magnetostriction of the FMM grains under a magnetic field. Considering the competing effects of the conductive filament and local Joule self-heating at grain boundaries on the transport properties, the dissimilar ER effects in the two thinner films are also understandable. These experimental findings provide an additional approach for tuning the magnetoresistive effect in manganite films.
 Strain-modulated ultrafast magneto-optic dynamics of graphene nanoflakes decorated with transition-metal atoms Yiming Zhang(张一鸣), Jing Liu(刘景), Chun Li(李春), Wei Jin(金蔚), Georgios Lefkidis, and Wolfgang Hübner Chin. Phys. B, 2021, 30 (9):  097702.  DOI: 10.1088/1674-1056/abeef1 Abstract ( 47 )   HTML ( 0 )   PDF (1137KB) ( 10 )   We perform first-principles calculations and coherent laser-matter interaction analyses to investigate the laser-induced ultrafast spin flip on graphene nanoflakes (GNFs) with transition metal elements attached on the boundary [TM&GNFs (TM=Fe, Co, Ni)]. It is shown that the spin-flip process on TM&GNFs is highly influenced by the involved element species and the position attached to the nanoflakes. Furthermore, taking Ni&GNF as an example, the first-principles tensile test predicts that the variation of the C-Ni bond length plays an important role in the spin density distribution, especially for the low-lying magnetic states, and can therefore dominate the spin-flip processes. The fastest spin-flip scenario is achieved within 80 fs in a Ni&GNF structure under 10% tensile strain along the C-Ni bond. The local deformation modulation of spin flip provides the precursory guidance for further study of ultrafast magnetization control in GNFs, which could lead to potential applications in future integrated straintronic devices.
 Analysis of properties of krypton ion-implanted Zn-polar ZnO thin films Qing-Fen Jiang(姜清芬), Jie Lian(连洁), Min-Ju Ying(英敏菊), Ming-Yang Wei(魏铭洋), Chen-Lin Wang(王宸琳), and Yu Zhang(张裕) Chin. Phys. B, 2021, 30 (9):  097801.  DOI: 10.1088/1674-1056/abe92e Abstract ( 37 )   HTML ( 0 )   PDF (1019KB) ( 10 )   The optical properties of materials are of great significance for their device applications. Different numbers of krypton ions are doped into high-quality Zn-polar ZnO films fabricated by molecular beam epitaxy (MBE) on sapphire substrates through ion implantation. Krypton is chemically inert. The structures, morphologies, and optical properties of films are measured. The x-ray diffraction (XRD) spectra confirm the wurtzite structures of Zn-polar ZnO films. Atomic force microscopy (AFM) results show that the films have pit surface structure and higher roughness after Kr ion implantation. A detailed investigation of the optical properties is performed by using the absorption spectrum, photoluminescence (PL), and spectroscopic ellipsometry (SE). The absorption spectrum is measured by UV-visible spectrophotometer and the bandgap energy is estimated by the Tauc method. The results show that the absorption increases and the bandgap decreases after Kr ion implantation. Moreover, the Kr ion implantation concentration also affects the properties of the film. The ellipsometry results show that the films' refractive index decreases with the Kr ion implantation concentration increasing. These results can conduce to the design and optimization of Kr ion-implanted polar ZnO films for optoelectronic applications.
 Influence of sulfur doping on the molecular fluorophore and synergistic effect for citric acid carbon dots Guohua Cao(曹国华), Zhifei Wei(魏志飞), Yuehong Yin(殷月红), Lige Fu(付丽歌), Yukun Liu(刘玉坤), Shengli Qiu(邱胜利), and Baoqing Zhang(张宝庆) Chin. Phys. B, 2021, 30 (9):  097802.  DOI: 10.1088/1674-1056/abfbd5 Abstract ( 45 )   HTML ( 0 )   PDF (1921KB) ( 13 )   In citric acid-based carbon dots, molecular fluorophore contributes greatly to the fluorescence emission. In this paper, the nitrogen and sulfur co-doped carbon dots (N,S-CDs) were prepared, and an independent sulfur source is selected to achieve the doping controllability. The influence of sulfur doping on the molecular fluorophore was systematically studied. The introduction of sulfur atoms may promote the formation of molecular fluorophore due to the increased nitrogen content in CDs. The addition surface states containing sulfur were produced, and S element exists as -SO3, and -SO4 groups. Appreciate ratio of nitrogen and sulfur sources can improve the fluorescence emission. The photoluminescence quantum yields (PLQY) is increased from 56.4% of the single N-doping CDs to 63.4% of double-doping CDs, which ascribes to the synergistic effect of molecular fluorophores and surface states. The sensitivity of fluorescence to pH response and various metal ions was also explored.
 Enhanced absorption process in the thin active region of GaAs based p-i-n structure Chen Yue(岳琛), Xian-Sheng Tang(唐先胜), Yang-Feng Li(李阳锋), Wen-Qi Wang(王文奇), Xin-Xin Li(李欣欣), Jun-Yang Zhang(张珺玚), Zhen Deng(邓震), Chun-Hua Du(杜春花), Hai-Qiang Jia(贾海强), Wen-Xin Wang(王文新), Wei Lu(陆卫), Yang Jiang(江洋), and Hong Chen(陈弘) Chin. Phys. B, 2021, 30 (9):  097803.  DOI: 10.1088/1674-1056/abf10c Abstract ( 59 )   HTML ( 0 )   PDF (1115KB) ( 46 )   The optical absorption is the most important macroscopic process to characterize the microscopic optical transition in the semiconductor materials. Recently, great enhancement has been observed in the absorption of the active region within a p-n junction. In this paper, GaAs based p-i-n samples with the active region varied from 100 nm to 3 μ were fabricated and it was observed that the external quantum efficiencies are higher than the typical results, indicating a new mechanism beyond the established theories. We proposed a theoretical model about the abnormal optical absorption process in the active region within a strong electric field, which might provide new theories for the design of the solar cells, photodetectors, and other photoelectric devices.
 Origin of anomalous enhancement of the absorption coefficient in a PN junction Xiansheng Tang(唐先胜), Baoan Sun(孙保安), Chen Yue(岳琛), Xinxin Li(李欣欣), Junyang Zhang(张珺玚), Zhen Deng(邓震), Chunhua Du(杜春花), Wenxin Wang(王文新), Haiqiang Jia(贾海强), Yang Jiang(江洋), Weihua Wang(汪卫华), and Hong Chen(陈弘) Chin. Phys. B, 2021, 30 (9):  097804.  DOI: 10.1088/1674-1056/ac0791 Abstract ( 36 )   HTML ( 0 )   PDF (637KB) ( 17 )   The absorption coefficient is usually considered as a constant for certain materials at the given wavelength. However, recent experiments demonstrated that the absorption coefficient could be enhanced a lot by the PN junction. The absorption coefficient varies with the thickness of the intrinsic layer in a PIN structure. Here, we interpret the anomalous absorption coefficient from the competition between recombination and drift for non-equilibrium carriers. Based on the Fokker-Planck theory, a non-equilibrium statistical model that describes the relationship between absorption coefficient and material thickness has been proposed. It could predict the experimental data well. Our results can give new ideas to design photoelectric devices.
 Exciton emission dynamics in single InAs/GaAs quantum dots due to the existence of plasmon-field-induced metastable states in the wetting layer Junhui Huang(黄君辉), Hao Chen(陈昊), Zhiyao Zhuo(卓志瑶), Jian Wang(王健), Shulun Li(李叔伦), Kun Ding(丁琨), Haiqiao Ni(倪海桥), Zhichuan Niu(牛智川), Desheng Jiang(江德生), Xiuming Dou(窦秀明), and Baoquan Sun(孙宝权) Chin. Phys. B, 2021, 30 (9):  097805.  DOI: 10.1088/1674-1056/ac0818 Abstract ( 57 )   HTML ( 0 )   PDF (984KB) ( 38 )   A very long lifetime exciton emission with non-single exponential decay characteristics has been reported for single InA-s/GaAs quantum dot (QD) samples, in which there exists a long-lived metastable state in the wetting layer (WL) through radiative field coupling between the exciton emissions in the WL and the dipole field of metal islands. In this article we have proposed a new three-level model to simulate the exciton emission decay curve. In this model, assuming that the excitons in a metastable state will diffuse and be trapped by QDs, and then emit fluorescence in QDs, a stretched-like exponential decay formula is derived as $I\left( t \right)=A\, t^{\beta -1}{\rm e}^{-\left( rt \right)^{\beta }}$, which can describe well the long lifetime decay curve with an analytical expression of average lifetime $\langle\tau\rangle=\frac{1}{r}\mathrm{\Gamma } ( \frac{1}{\beta }+1 )$，where $\Gamma$ is the Gamma function. Furthermore, based on the proposed three-level model, an expression of the second-order auto-correlation function $g^{2}\left( t \right)$ which can fit the measured $g^{2}\left( t \right)$ curve well, is also obtained.
 Topology optimization method of metamaterials design for efficient enhanced transmission through arbitrary-shaped sub-wavelength aperture Pengfei Shi(史鹏飞), Yangyang Cao(曹阳阳), Hongge Zhao(赵宏革), Renjing Gao(高仁璟), and Shutian Liu(刘书田) Chin. Phys. B, 2021, 30 (9):  097806.  DOI: 10.1088/1674-1056/ac0cde Abstract ( 72 )   HTML ( 0 )   PDF (3283KB) ( 61 )   The electromagnetic wave enhanced transmission (ET) through the sub-wavelength aperture was an unconventional physical phenomenon with great application potential. It was important to find a general design method which can realize efficient ET for arbitrary-shaped apertures. For achieving ET with maximum efficiency at specific frequency through arbitrary-shaped subwavelength aperture, a topology optimization method for designing metamaterials (MTM) microstructure was proposed in this study. The MTM was employed and inserted vertically in the aperture. The description function for the arbitrary shape of the aperture was established. The optimization model was founded to search the optimal MTM microstructure for maximum enhanced power transmission through the aperture at the demanded frequency. Several MTM microstructures for ET through the apertures with different shapes at the demanded frequency were designed as examples. The simulation and experimental results validate the feasibility of the method. The regularity of the optimal ET microstructures and their advantages over the existing configurations were discussed.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
 Direct growth of graphene films without catalyst on flexible glass substrates by PECVD Rui-Xia Miao(苗瑞霞), Chen-He Zhao(赵晨鹤), Shao-Qing Wang(王少青), Wei Ren(任卫), Yong-Feng Li(李永锋), Ti-Kang Shu(束体康), and Ben Yang(杨奔) Chin. Phys. B, 2021, 30 (9):  098101.  DOI: 10.1088/1674-1056/abeeec Abstract ( 50 )   HTML ( 0 )   PDF (2157KB) ( 14 )   A hydrogen-plasma-etching-based plasma-enhanced chemical vapor deposition (PECVD) synthesis route without metal catalyst for preparing the graphene films on flexible glass is developed. The quality of the prepared graphene films is evaluated by scanning electron microscopy, x-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, ultraviolet-visible spectroscopy, and electrochemical measurements. In a radio frequency (RF) power range of 50 W-300 W, the graphene growth rate increases with RF power increasing, while the intensity ratio of D- to G-Raman peak (ID/IG) decreases. When the RF power is higher than 300 W, the ID/IG rises again. By optimizing experimental parameters of hydrogen plasma etching and RF power, the properties of as-prepared flexible graphene on glass are modulated to be able to achieve the graphene's transparency, good electrical conductivity, and better macroscopic uniformity. Direct growth of graphene film without any metal catalyst on flexible glass can be a promising candidate for applications in flexible transparent optoelectronics.
 A multi-band and polarization-independent perfect absorber based on Dirac semimetals circles and semi-ellipses array Zhiyou Li(李治友), Yingting Yi(易颖婷), Danyang Xu(徐丹阳), Hua Yang(杨华), Zao Yi(易早), Xifang Chen(陈喜芳), Yougen Yi(易有根), Jianguo Zhang(张建国), and Pinghui Wu(吴平辉) Chin. Phys. B, 2021, 30 (9):  098102.  DOI: 10.1088/1674-1056/abfb57 Abstract ( 68 )   HTML ( 2 )   PDF (1064KB) ( 24 )   We design a four-band terahertz metamaterial absorber that relied on the block Dirac semi-metal (BDS). It is composed of a Dirac material layer, a gold reflecting layer, and a photonic crystal slab (PCS) medium layer. This structure achieved perfect absorption of over 97% at 4.06 THz, 6.15 THz, and 8.16 THz. The high absorption can be explained by the localized surface plasmon resonance (LSPR). And this conclusion can be proved by the detailed design of the surface structure. Moreover, the resonant frequency of the device can be dynamically tuned by changing the Fermi energy of the BDS. Due to the advantages such as high absorption, adjustable resonance, and anti-interference of incident angle and polarization mode, the Dirac semi-metal perfect absorber (DSPA) has great potential value in fields such as biochemical sensing, information communication, and nondestructive detection.
 Low temperature ferromagnetism in CaCu3Ti4O12 Song Yang(杨松), Xiao-Jing Luo(罗晓婧), Zhi-Ming Shen(申志明), Tian Gao(高湉), Yong-Sheng Liu(刘永生), and Shao-Long Tang(唐少龙) Chin. Phys. B, 2021, 30 (9):  098103.  DOI: 10.1088/1674-1056/abeef0 Abstract ( 44 )   HTML ( 0 )   PDF (2128KB) ( 10 )   The low-temperature magnetic order behaviors of perovskite oxide CaCu3Ti4O12 (CCTO) ceramics prepared by different methods are discussed. X-ray diffraction, scanning electron microscope, x-ray photoelectron spectroscopy, and direct current (DC) magnetization are used to characterize the structures, microscopic morphologies, valence states, and magnetic properties of the samples. The results show that the magnetic behaviors of CCTO ceramics are very sensitive to the preparation process. The quenched CCTO ceramic and CCTO powders grown in a molten salt crystal, which contain much more oxygen vacancies and Ti3+, show the coexistence of weak ferromagnetic order and antiferromagnetic order below the Neel temperature. It suggests that the bound magnetopolaron formed by oxygen vacancies and Ti3+ ion composite defects are responsible for the weak ferromagnetic order at low temperature.
 Analysis on diffusion-induced stress for multi-layer spherical core-shell electrodes in Li-ion batteries Siyuan Yang(杨思源), Chuanwei Li(李传崴), Zhifeng Qi(齐志凤), Lipan Xin(辛立攀), Linan Li(李林安), Shibin Wang(王世斌), and Zhiyong Wang(王志勇) Chin. Phys. B, 2021, 30 (9):  098201.  DOI: 10.1088/1674-1056/ac11de Abstract ( 54 )   HTML ( 0 )   PDF (789KB) ( 46 )   Silicon-based carbon composites are believed as promising anodes in the near future due to their outstanding specific capacity and relatively lower volume effect compared to pure silicon anodes. Herein, a multilayer spherical core-shell (M-SCS) electrode with a graphite framework prepared with Si@O-MCMB/C nanoparticles is developed, which aims to realize chemically/mechanically stability during the lithiation/delithiation process with high specific capacity. An electrochemical-/mechanical-coupling model for the M-SCS structure is established with various chemical/mechanical boundary conditions. The simulation of finite difference method (FDM) has been conducted based on the proposed coupling model, by which the diffusion-induced stress along both the radial and the circumferential directions is determined. Moreover, factors that influence the diffusion-induced stress of the M-SCS structure have been discussed and analyzed in detail.
 Temperature and current sensitivity extraction of optical superconducting transition-edge sensors based on a two-fluid model Yue Geng(耿悦), Pei-Zhan Li(李佩展), Jia-Qiang Zhong(钟家强), Wen Zhang(张文), Zheng Wang(王争), Wei Miao(缪巍), Yuan Ren(任远), and Sheng-Cai Shi(史生才) Chin. Phys. B, 2021, 30 (9):  098501.  DOI: 10.1088/1674-1056/ac11ce Abstract ( 50 )   HTML ( 0 )   PDF (1962KB) ( 32 )   Optical superconducting transition-edge sensor (TES) has been widely used in quantum information, biological imaging, and fluorescence microscopy owing to its high quantum efficiency, low dark count, and photon number resolving capability. The temperature sensitivity (αI) and current sensitivity (βI) are important parameters for optical TESs, which are generally extracted from the complex impedance. Here we present a method to extract αI and βI based on a two-fluid model and compare the calculated current-voltage curves, pulse response, and theoretical energy resolution with the measured ones. This method shows qualitative agreement that is suitable for further optimization of optical TESs.
 C band microwave damage characteristics of pseudomorphic high electron mobility transistor Qi-Wei Li(李奇威), Jing Sun(孙静), Fu-Xing Li(李福星), Chang-Chun Chai(柴常春), Jun Ding(丁君), and Jin-Yong Fang(方进勇) Chin. Phys. B, 2021, 30 (9):  098502.  DOI: 10.1088/1674-1056/abf135 Abstract ( 55 )   HTML ( 0 )   PDF (3175KB) ( 22 )   The damage effect characteristics of GaAs pseudomorphic high electron mobility transistor (pHEMT) under the irradiation of C band high-power microwave (HPM) is investigated in this paper. Based on the theoretical analysis, the thermoelectric coupling model is established, and the key damage parameters of the device under typical pulse conditions are predicted, including the damage location, damage power, etc. By the injection effect test and device microanatomy analysis through using scanning electron microscope (SEM) and energy dispersive spectrometer (EDS), it is concluded that the gate metal in the first stage of the device is the vulnerable to HPM damage, especially the side below the gate near the source. The damage power in the injection test is about 40 dBm and in good agreement with the simulation result. This work has a certain reference value for microwave damage assessment of pHEMT.
 Design and optimization of a nano-antenna hybrid structure for solar energy harvesting application Mohammad Javad Rabienejhad, Mahdi Davoudi-Darareh, and Azardokht Mazaheri Chin. Phys. B, 2021, 30 (9):  098503.  DOI: 10.1088/1674-1056/abea8e Abstract ( 43 )   HTML ( 0 )   PDF (6570KB) ( 15 )   A novel hybrid structure with high responsivity and efficiency is proposed based on an L-shaped frame nano-antenna (LSFNA) array for solar energy harvesting application. So, two types of LSFNAs are designed and optimized to enhance the harvesting characteristics of traditional simple electric dipole nano-antenna (SEDNA). The LSFNA geometrical dimensions are optimized to have the best values for the required input impedance at three resonance wavelengths of λres = 10 μm, 15 μm, and 20 μm. Then the LSFNAs with three different sizes are modeled like a planar spiral-shaped array (PSSA). Also, a fractal bowtie nano-antenna is connected with the PSSA in the array gap. This proposed hybrid structure consists of two main elements: (I) Three different sizes of the LSFNAs with two different material types are designed based on the thin-film metal-insulator-metal diodes that are a proper method for infrared energy harvesting. (Ⅱ) The PSSA gap is designed based on the electron field emission proposed by the Fowler-Nordheim theory for the array rectification. Finally, the proposed device is analyzed. The results show that the PSSA not only has an averaged 3-time enhancement in the harvesting characteristics (such as return loss, harvesting efficiency, etc.) than the previously proposed structures but also is a multi-resonance wide-band device. Furthermore, the proposed antenna takes up less space in the electronic circuit and has an easy implementation process.
 Device design based on the covalent homocouplingof porphine molecules Minghui Qu(曲明慧), Jiayi He(贺家怡), Kexin Liu(刘可心), Liemao Cao(曹烈茂), Yipeng Zhao(赵宜鹏), Jing Zeng(曾晶), and Guanghui Zhou(周光辉) Chin. Phys. B, 2021, 30 (9):  098504.  DOI: 10.1088/1674-1056/abeb0c Abstract ( 36 )   HTML ( 2 )   PDF (2984KB) ( 13 )   Porphine has a great potential application in molecular electronic devices. In this work, based on the density functional theory (DFT) and combining with nonequilibrium Green's function (NEGF), we study the transport properties of the molecular devices constructed by the covalent homocoupling of porphine molecules conjunction with zigzag graphene nanoribbons electrodes. We find that different couple phases bring remarkable differences in the transport properties. Different coupling phases have different application prospects. We analyze and discuss the differences in transport properties through the molecular energy spectrum, electrostatic difference potential, local density of states (LDOS), and transmission pathway. The results are of great significance for the design of porphine molecular devices in the future.
 Pyramid scheme in stock market: A kind of financial market simulation Yong Shi(石勇), Bo Li(李博), and Guang-Le Du(杜光乐) Chin. Phys. B, 2021, 30 (9):  098901.  DOI: 10.1088/1674-1056/abeef3 Abstract ( 91 )   HTML ( 0 )   PDF (652KB) ( 24 )   Artificial stock market simulation based on agent is an important means to study financial market. Based on the assumption that the investors are composed of a main fund, small trend and contrarian investors characterized by four parameters, we simulate and research a kind of financial phenomenon with the characteristics of pyramid schemes. Our simulation results and theoretical analysis reveal the relationships between the rate of return of the main fund and the proportion of the trend investors in all small investors, the small investors' parameters of taking profit and stopping loss, the order size of the main fund and the strategies adopted by the main fund. Our work is helpful to explain the financial phenomenon with the characteristics of pyramid schemes in financial markets, design trading rules for regulators and develop trading strategies for investors.
 Experimental study on age and gender differences in microscopic movement characteristics of students Jiayue Wang(王嘉悦), Maik Boltes, Armin Seyfried, Antoine Tordeux, Jun Zhang(张俊), and Wenguo Weng(翁文国) Chin. Phys. B, 2021, 30 (9):  098902.  DOI: 10.1088/1674-1056/ac11d4 Abstract ( 57 )   HTML ( 1 )   PDF (2334KB) ( 58 )   Campus security has aroused many concerns from the whole society. Stampede is one of the most frequent and influential accidents in campus. Studies on pedestrian dynamics especially focusing on students are essential for campus security, which are helpful to improve facility design and emergency evacuation strategy. In this paper, primary and middle school students were recruited to participate in the single-file experiments. The microscopic movement characteristics, including walking speed, headway, gait characteristics (step length, step frequency and swaying amplitude) and their relations were investigated. Age and gender differences in the headway-speed diagram and space requirements were analyzed by statistical tests. The results indicated that the impacts of age and gender were significant. There were three stages for the influence of gender on the headway-speed diagram for both age groups. The impacts on students' space requirements were consistent for different age and gender groups. But the impacts of age and gender on free-flow speed were affected by each other. Due to the connection of walking speed and gait characteristics, the comparisons of gait characteristics between different ages and genders were performed to understand the corresponding differences in speed more deeply. The results showed that differences in step length and swaying amplitude between males and females were significant for both age groups. The effect of gender on step frequency was significant for primary students. But for middle school students, whether gender had significant impact on step frequency was not clear here because of the large P-value. Besides, the influence of age on gait characteristics changed with gender.
 Using agent-based simulation to assess diseaseprevention measures during pandemics Yunhe Tong(童蕴贺), Christopher King, and Yanghui Hu(胡杨慧) Chin. Phys. B, 2021, 30 (9):  098903.  DOI: 10.1088/1674-1056/ac0ee8 Abstract ( 68 )   HTML ( 0 )   PDF (544KB) ( 36 )   Despite the growing interest in macroscopic epidemiological models to deal with threats posed by pandemics such as COVID-19, little has been done regarding the assessment of disease spread in day-to-day life, especially within buildings such as supermarkets where people must obtain necessities at the risk of exposure to disease. Here, we propose an integrated customer shopping simulator including both shopper movement and choice behavior, using a force-based and discrete choice model, respectively. By a simple extension to the force-based model, we implement the following preventive measures currently taken by supermarkets; social distancing and one-way systems, and different customer habits, assessing them based on the average individual disease exposure and the time taken to complete shopping (shopping efficiency). Results show that maintaining social distance is an effective way to reduce exposure, but at the cost of shopping efficiency. We find that the one-way system is the optimal strategy for reducing exposure while minimizing the impact on shopping efficiency. Customers should also visit supermarkets less frequently, but buy more when they do, if they wish to minimize their exposure. We hope that this work demonstrates the potential of pedestrian dynamics simulations in assessing preventative measures during pandemics, particularly if it is validated using empirical data.
ERRATUM
 Erratum to “Simultaneous effects of magnetic field and space porosity on compressible Maxwell fluid transport induced by a surface acoustic wave in a microchannel” Khaled S. Mekheimer, Soliman R. Komy, and Sara I. Abdelsalam Chin. Phys. B, 2021, 30 (9):  099901.  DOI: 10.1088/1674-1056/ac2252 Abstract ( 34 )   HTML ( 0 )   PDF (354KB) ( 10 )   We would like to acknowledge the misprinted terms in our published paper “Simultaneous effects of magnetic field and space porosity on compressible Maxwell fluid transport induced by a surface acoustic wave in a microchannel” [Chin. Phys. B 22 124702 (2013)]. Since only two misprints exist and the main results of the published paper are correct, we present the correct equations in this erratum.
 Erratum to “Designing thermal demultiplexer: Splitting phonons by negative mass and genetic algorithm optimization” Yu-Tao Tan(谭宇涛), Lu-Qin Wang(王鲁钦), Zi Wang(王子), Jiebin Peng(彭洁彬), and Jie Ren(任捷) Chin. Phys. B, 2021, 30 (9):  099902.  DOI: 10.1088/1674-1056/ac23d6 Abstract ( 39 )   HTML ( 0 )   PDF (391KB) ( 16 )   Equations (8) and (9) in the original paper [Chin. Phys. B 30 036301 (2021)] are corrected.
ISSN 1674-1056   CN 11-5639/O4
, Vol. 30, No. 9