17 December 2020, Volume 30 Issue 1
TOPICAL REVIEW—Twistronics
 Correlated insulating phases in the twisted bilayer graphene Yuan-Da Liao(廖元达), Xiao-Yan Xu(许霄琰), Zi-Yang Meng(孟子杨), and Jian Kang(康健) Chin. Phys. B, 2021, 30 (1):  017305.  DOI: 10.1088/1674-1056/abcfa3 Abstract ( 325 )   HTML ( 7 )   PDF (1150KB) ( 334 )   We review analytical and numerical studies of correlated insulating states in twisted bilayer graphene, focusing on real-space lattice models constructions and their unbiased quantum many-body solutions. We show that by constructing localized Wannier states for the narrow bands, the projected Coulomb interactions can be approximated by interactions of cluster charges with assisted nearest neighbor hopping terms. With the interaction part only, the Hamiltonian is SU(4) symmetric considering both spin and valley degrees of freedom. In the strong coupling limit where the kinetic terms are neglected, the ground states are found to be in the SU(4) manifold with degeneracy. The kinetic terms, treated as perturbation, break this large SU(4) symmetry and propel the appearance of intervalley coherent state, quantum topological insulators, and other symmetry-breaking insulating states. We first present the theoretical analysis of moir\'e lattice model construction and then show how to solve the model with large-scale quantum Monte Carlo simulations in an unbiased manner. We further provide potential directions such that from the real-space model construction and its quantum many-body solutions how the perplexing yet exciting experimental discoveries in the correlation physics of twisted bilayer graphene can be gradually understood. This review will be helpful for the readers to grasp the fast growing field of the model study of twisted bilayer graphene.
SPECIAL TOPIC—Unconventional superconductivity
 Tip-induced superconductivity commonly existing in the family of transition-metal dipnictides MPn2 Meng-Di Zhang(张孟迪), Sheng Xu(徐升), Xing-Yuan Hou(侯兴元), Ya-Dong Gu(谷亚东), Fan Zhang(张凡), Tian-Long Xia(夏天龙), Zhi-An Ren(任治安), Gen-Fu Chen(陈根富), Ning Hao(郝宁), and Lei Shan(单磊) Chin. Phys. B, 2021, 30 (1):  017304.  DOI: 10.1088/1674-1056/abccbb Abstract ( 103 )   HTML ( 5 )   PDF (1255KB) ( 67 )   We report the tip-induced superconductivity on the topological semimetal NbSb2, similar to the observation on TaAs2 and NbAs2. Belonging to the same family of MPn2, all these materials possess similar band structures, indicating that the tip-induced superconductivity may be closely related to their topological nature and share a common mechanism. Further analysis suggests that a bulk band should play the dominant role in such local superconductivity most likely through interface coupling. In addition, the compatibility between the induced superconductivity and tips' ferromagnetism gives an evidence for its unconventional nature. These results provide further clues to elucidate the mechanism of the tip-induced superconductivity observed in topological materials.
SPECIAL TOPIC—Modeling and simulations for the structures and functions of proteins and nucleic acids
 Protein-protein docking with interface residue restraints Hao Li(李豪) and Sheng-You Huang(黄胜友) Chin. Phys. B, 2021, 30 (1):  018703.  DOI: 10.1088/1674-1056/abc14e Abstract ( 1 )   HTML ( 0 )   PDF (658KB) ( 163 )   The prediction of protein-protein complex structures is crucial for fundamental understanding of celluar processes and drug design. Despite significant progresses in the field, the accuracy of ab initio docking without using any experimental restraints remains relatively low. With the rapid advancement of structural biology, more and more information about binding can be derived from experimental data such as NMR experiments or chemical cross-linking. In addition, information about the residue contacts between proteins may also be derived from their sequences by using evolutionary analysis or deep learning. Here, we propose an efficient approach to incorporate interface residue restraints into protein-protein docking, which is named as HDOCKsite. Extensive evaluations on the protein-protein docking benchmark 4.0 showed that HDOCKsite significantly improved the docking performance and obtained a much higher success rate in binding mode predictions than original ab initio docking.
TOPICAL REVIEW—Ultracold atom and its application in precision measurement
 Cold atom clocks and their applications in precision measurements Shao-Yang Dai(戴少阳), Fa-Song Zheng(郑发松), Kun Liu(刘昆), Wei-Liang Chen(陈伟亮), Yi-Ge Lin(林弋戈), Tian-Chu Li(李天初), and Fang Fang(房芳) Chin. Phys. B, 2021, 30 (1):  013701.  DOI: 10.1088/1674-1056/abbbee Abstract ( 196 )   HTML ( 4 )   PDF (3844KB) ( 216 )   Cold atom clocks have made remarkable progresses in the last two decades and played critical roles in precision measurements. Primary Cs fountain frequency standards have achieved a total uncertainty of a few parts in 1016, and the best optical clock has reached a type B uncertainty below 10-18. Besides applications in the metrology, navigation, etc., ultra-stable and ultra-accurate atomic clocks have also become powerful tools in the basic scientific investigations. In this paper, we focus on the recent developments in the high-performance cold atomic clocks which can be used as frequency standards to calibrate atomic time scales. The basic principles, performances, and limitations of fountain clocks and optical clocks based on signal trapped ion or neutral atoms are summarized. Their applications in metrology and other areas are briefly introduced.
 Improve the performance of interferometer with ultra-cold atoms Xiangyu Dong(董翔宇), Shengjie Jin(金圣杰), Hongmian Shui(税鸿冕), Peng Peng(彭鹏), and Xiaoji Zhou(周小计) Chin. Phys. B, 2021, 30 (1):  014210.  DOI: 10.1088/1674-1056/abcf33 Abstract ( 157 )   HTML ( 2 )   PDF (3289KB) ( 195 )   Ultra-cold atoms provide ideal platforms for interferometry. The macroscopic matter-wave property of ultra-cold atoms leads to large coherent length and long coherent time, which enable high accuracy and sensitivity to measurement. Here, we review our efforts to improve the performance of the interferometer. We demonstrate a shortcut method for manipulating ultra-cold atoms in an optical lattice. Compared with traditional ones, this shortcut method can reduce the manipulation time by up to three orders of magnitude. We construct a matter-wave Ramsey interferometer for trapped motional quantum states and significantly increase its coherence time by one order of magnitude with an echo technique based on this method. Efforts have also been made to enhance the resolution by multimode scheme. Application of a noise-resilient multi-component interferometer shows that increasing the number of paths could sharpen the peaks in the time-domain interference fringes, which leads to a resolution nearly twice compared with that of a conventional double-path two-mode interferometer. With the shortcut method mentioned above, improvement of the momentum resolution could also be fulfilled, which leads to atomic momentum patterns less than 0.6 $$\hbar k_L$$. To identify and remove systematic noises, we introduce the methods based on the principal component analysis (PCA) that reduce the noise in detection close to the $$1/\sqrt2$$ of the photon-shot noise and separate and identify or even eliminate noises. Furthermore, we give a proposal to measure precisely the local gravity acceleration within a few centimeters based on our study of ultracold atoms in precision measurements.
SPECIAL TOPIC—Ultracold atom and its application in precision measurement
 Ultradilute self-bound quantum droplets in Bose-Bose mixtures at finite temperature Jia Wang(王佳), Xia-Ji Liu(刘夏姬), and Hui Hu(胡辉) Chin. Phys. B, 2021, 30 (1):  010306.  DOI: 10.1088/1674-1056/abd2ad Abstract ( 116 )   HTML ( 3 )   PDF (819KB) ( 67 )   We theoretically investigate the finite-temperature structure and collective excitations of a self-bound ultradilute Bose droplet in a flat space realized in a binary Bose mixture with attractive inter-species interactions on the verge of mean-field collapse. As the droplet formation relies critically on the repulsive force provided by Lee-Huang-Yang quantum fluctuations, which can be easily compensated by thermal fluctuations, we find a significant temperature effect in the density distribution and collective excitation spectrum of the Bose droplet. A finite-temperature phase diagram as a function of the number of particles is determined. We show that the critical number of particles at the droplet-to-gas transition increases dramatically with increasing temperature. Towards the bulk threshold temperature for thermally destabilizing an infinitely large droplet, we find that the excitation-forbidden, self-evaporation region in the excitation spectrum, predicted earlier by Petrov using a zero-temperature theory, shrinks and eventually disappears. All the collective excitations, including both surface modes and compressional bulk modes, become softened at the droplet-to-gas transition. The predicted temperature effects of a self-bound Bose droplet in this work could be difficult to measure experimentally due to the lack of efficient thermometry at low temperatures. However, these effects may already present in the current cold-atom experiments.
 Theoretical study of the hyperfine interaction constants, Landé g-factors, and electric quadrupole moments for the low-lying states of the 61Ni q+ ( q= 11, 12, 14 , and 15) ions Ting-Xian Zhang(张婷贤), Yong-Hui Zhang(张永慧), Cheng-Bin Li(李承斌), and Ting-Yun Shi(史庭云) Chin. Phys. B, 2021, 30 (1):  013101.  DOI: 10.1088/1674-1056/abc7a3 Abstract ( 102 )   HTML ( 2 )   PDF (645KB) ( 65 )   Highly charged nickel ions have been suggested as candidates for the ultra-precise optical clock, meanwhile the relevant experiment has been carried out. In the framework of the multiconfiguration Dirac-Hartree-Fock (MCDHF) method, we calculated the hyperfine interaction constants, the Landé g-factors, and the electric quadrupole moments for the low-lying states in the 61Ni11+, 61Ni12+, 61Ni14+, and 61Ni15+ ions. These states are clock states of the selected clock transitions in highly charged nickel ions (see Fig. \fref1 1). Based on discussing the effects of the electron correlations, the Breit interaction, and quantum electrodynamics (QED) effect on these physical quantities, reasonable uncertainties were obtained for our calculated results. In addition, the electric quadrupole frequency shifts and the Zeeman frequency shifts of the clock transitions concerned were analyzed.
INVITED REVIEW
 57Fe Mössbauer spectrometry: A powerful technique to analyze the magnetic and phase characteristics in RE-Fe-B permanent magnets Lizhong Zhao(赵利忠), Xuefeng Zhang(张雪峰), Mi Yan(严密), Zhongwu Liu(刘仲武), and Jean-Marc Greneche Chin. Phys. B, 2021, 30 (1):  013302.  DOI: 10.1088/1674-1056/abc53d Abstract ( 98 )   HTML ( 1 )   PDF (5702KB) ( 63 )   This review summarizes the recent advances on the application of 57Fe Mössbauer spectrometry to study the magnetic and phase characteristics of Nd-Fe-B-based permanent magnets. First of all, the hyperfine structures of the Ce2Fe14B, (Ce, Nd)2Fe14B and MM2Fe14B phases are well-defined by using the model based on the Wigner-Seitz analysis of the crystal structure. The results show that the isomer shift δ and the quadrupole splitting ∆ E Q of those 2:14:1 phases show minor changes with the Nd content, while the hyperfine field B hf increases monotonically with increasing Nd content and its value is influenced by the element segregation and phase separation in the 2:14:1 phase. Then, the hyperfine structures of the low fraction secondary phases are determined by the 57Fe Mössbauer spectrometry due to its high sensitivity. On this basis, the content, magnetic behavior, and magnetization of the REFe2 phase, the amorphous grain boundary (GB) phase, and the amorphous worm-like phase, as well as their effects on the magnetic properties, are systematically studied.
REVIEW
 Functionalized magnetic nanoparticles for drug delivery in tumor therapy Ruo-Nan Li(李若男), Xian-Hong Da(达先鸿), Xiang Li (李翔), Yun-Shu Lu(陆云姝), Fen-Fen Gu(顾芬芬), and Yan Liu(刘艳) Chin. Phys. B, 2021, 30 (1):  017502.  DOI: 10.1088/1674-1056/abb3e6 Abstract ( 63 )   HTML ( 1 )   PDF (1015KB) ( 49 )   The side effects of chemotherapy are mainly the poor control of drug release. Magnetic nanoparticles (MNPs) have super-paramagnetic behaviors which are preferred for biomedical applications such as in targeted drug delivery, besides, in magnetic recording, catalysis, and others. MNPs, due to high magnetization response, can be manipulated by the external magnetic fields to penetrate directly into the tumor, thus they can act as ideal drug carriers. MNPs also play a crucial role in drug delivery system because of their high surface-to-volume ratio and porosity. The drug delivery in tumor therapy is related to the sizes, shapes, and surface coatings of MNPs as carriers. Therefore, in this review, we first summarize the effects of the sizes, shapes, and surface coatings of MNPs on drug delivery, then discuss three types of drug release systems, i.e., pH-controlled, temperature-controlled, and magnetic-controlled drug release systems, and finally compare the principle of passive drug release with that of active drug release in tumor therapy.
RAPID COMMUNICATION
 Surface active agents stabilize nanodroplets and enhance haze formation Yunqing Ma(马韵箐), Changsheng Chen(陈昌盛), and Xianren Zhang(张现仁) Chin. Phys. B, 2021, 30 (1):  010504.  DOI: 10.1088/1674-1056/abca1e Abstract ( 159 )   HTML ( 1 )   PDF (740KB) ( 72 )   Although many organic molecules found commonly in the atmosphere are known to be surface-active in aqueous solutions, their effects on the mechanisms underlying haze formation remain unclear. In this paper, based on a simple thermodynamic analysis, we report that the adsorption of amphiphilic organics alone not only lowers the surface tension, but also unexpectedly stabilizes nanodroplets of specific size under water vapor supersaturation. Then we determine how various factors, including relative humidity, water activity effect due to dissolution of inorganic components as well as surface tension effect due to surface adsorption of organic components, cooperatively induce the stability of nanodroplets. The nanodroplet stability behaviors not captured in the current theory would change the formation mechanism of haze droplets, from the hygroscopic growth pathway to a nonclassical two-step nucleation pathway.
 Physical properties and phase diagram of NaFe1 -xVxAs Guang-Yang Dai(代光阳), Xin He(何鑫), Zhi-Wen Li(李芷文), Chang-Ling Zhang(张昌玲), Lu-Chuan Shi(史鲁川), Run-Ze Yu(于润泽), Xian-Cheng Wang(望贤成), and Chang-Qing Jin(靳常青) Chin. Phys. B, 2021, 30 (1):  017401.  DOI: 10.1088/1674-1056/abcf95 Abstract ( 110 )   HTML ( 1 )   PDF (1208KB) ( 90 )   We grew a series of NaFe1 -xVxAs (0 ≤ x ≤ 0.03) single crystals and performed the measurements of resistance, magnetic susceptibility, and specific heat to study the superconducting phase diagram by doping V into NaFeAs. Both the structural and the spin-density-wave (SDW) transitions are slightly suppressed by V-doping. While superconducting transition temperature is enhanced to the maximum value of ∼ 15 K when the optimal doping level x = 0.007 and then is suppressed rapidly with further V-doping, displaying a small superconducting dome. Our results suggest that V-impurities should act as strong magnetic scattering centers which cause the sharp suppression of superconductivity in NaFe1 - xVxAs.
 Doping effects of transition metals on the superconductivity of (Li,Fe)OHFeSe films Hot! Dong Li(李栋), Peipei Shen(沈沛沛), Sheng Ma(马晟), Zhongxu Wei(魏忠旭), Jie Yuan(袁洁), Kui Jin(金魁), Li Yu(俞理), Fang Zhou(周放), Xiaoli Dong(董晓莉), and Zhongxian Zhao(赵忠贤) Chin. Phys. B, 2021, 30 (1):  017402.  DOI: 10.1088/1674-1056/abd2ab Abstract ( 236 )   HTML ( 3 )   PDF (998KB) ( 311 )   The doping effects of transition metals (TMs = Mn, Co, Ni, and Cu) on the superconducting critical parameters are investigated in the films of iron selenide (Li,Fe)OHFeSe. The samples are grown via a matrix-assisted hydrothermal epitaxy method. Among the TMs, the elements of Mn and Co adjacent to Fe are observed to be incorporated into the crystal lattice more easily. It is suggested that the doped TMs mainly occupy the iron sites of the intercalated (Li,Fe)OH layers rather than those of the superconducting FeSe layers. We find that the critical current density J c can be enhanced much more strongly by the Mn dopant than the other TMs, while the critical temperature T c is weakly affected by the TM doping.
 High temperature strain glass in Ti-Au and Ti-Pt based shape memory alloys Hot! Shuai Ren(任帅), Chang Liu(刘畅), and Wei-Hua Wang(汪卫华) Chin. Phys. B, 2021, 30 (1):  018101.  DOI: 10.1088/1674-1056/abc54a Abstract ( 126 )   HTML ( 1 )   PDF (902KB) ( 128 )   Strain glass is a frozen short-range strain ordered state found in shape memory alloys recently, which exhibits novel properties around the ideal glass transition temperature T0. However, the T0 of current strain glass systems is still very low, limiting their potential applications and experimental studies. In this paper, we reported two new strain glass systems with relatively high T0. In Ti50Au50-xCrx alloys, the strain glass appears at x=25, and exhibits a T0 of 251 K, while in Ti50Pt50-yFey alloys, the strain glass takes place at y=30, and shows a T0 of 272 K. Both of them are comparable with the highest T0 value reported so far. Moreover, the phase diagrams of main strain glass systems in Ti-based alloys were summarized. It is found that the influence of the martensitic transformation temperature of the host alloy on the T0 of the strain glass is limited. This work may help to design new strain glass systems with higher T0 above ambient temperature.
 Edge-and strain-induced band bending in bilayer-monolayer Pb2Se3 heterostructures Hot! Peng Fan(范朋), Guojian Qian(钱国健), Dongfei Wang(王东飞), En Li(李恩), Qin Wang(汪琴), Hui Chen(陈辉), Xiao Lin(林晓), and Hong-Jun Gao(高鸿钧) Chin. Phys. B, 2021, 30 (1):  018105.  DOI: 10.1088/1674-1056/abcf92 Abstract ( 203 )   HTML ( 2 )   PDF (1091KB) ( 187 )   By using scanning tunneling microscope/microscopy (STM/STS), we reveal the detailed electronic structures around the sharp edges and strained terraces of lateral monolayer-bilayer Pd2Se3 heterostructures. We find that the edges of such heterostructures are well-defined zigzag type. Band bending and alignment are observed across the zigzag edge, forming a monolayer-bilayer heterojunction. In addition, an n-type band bending is induced by strain on a confined bilayer Pd2Se3 terrace. These results provide effective toolsets to tune the band structures in Pd2Se3-based heterostructures and devices.
GENERAL
 Two-dimensional finite element mesh generation algorithm for electromagnetic field calculation Chun-Feng Zhang(章春锋), Wei Wang(汪伟), Si-Guang An(安斯光), and Nan-Ying Shentu(申屠南瑛) Chin. Phys. B, 2021, 30 (1):  010101.  DOI: 10.1088/1674-1056/abaedf Abstract ( 92 )   HTML ( 2 )   PDF (1264KB) ( 54 )   Two-dimensional finite element mesh generation algorithm for electromagnetic field calculation is proposed in this paper to improve the efficiency and accuracy of electromagnetic calculation. An image boundary extraction algorithm is developed to map the image on the geometric domain. Identification algorithm for the location of nodes in polygon area is proposed to determine the state of the node. To promote the average quality of the mesh and the efficiency of mesh generation, a novel force-based mesh smoothing algorithm is proposed. One test case and a typical electromagnetic calculation are used to testify the effectiveness and efficiency of the proposed algorithm. The results demonstrate that the proposed algorithm can produce a high-quality mesh with less iteration.
 A meshless algorithm with the improved moving least square approximation for nonlinear improved Boussinesq equation Yu Tan(谭渝) and Xiao-Lin Li(李小林) Chin. Phys. B, 2021, 30 (1):  010201.  DOI: 10.1088/1674-1056/abaed7 Abstract ( 64 )   HTML ( 2 )   PDF (2015KB) ( 39 )   An improved moving least square meshless method is developed for the numerical solution of the nonlinear improved Boussinesq equation. After the approximation of temporal derivatives, nonlinear systems of discrete algebraic equations are established and are solved by an iterative algorithm. Convergence of the iterative algorithm is discussed. Shifted and scaled basis functions are incorporated into the method to guarantee convergence and stability of numerical results. Numerical examples are presented to demonstrate the high convergence rate and high computational accuracy of the method.
 High-order rational solutions and resonance solutions for a (3+1)-dimensional Kudryashov-Sinelshchikov equation Yun-Fei Yue(岳云飞), Jin Lin(林机), and Yong Chen(陈勇) Chin. Phys. B, 2021, 30 (1):  010202.  DOI: 10.1088/1674-1056/abb3f3 Abstract ( 111 )   HTML ( 1 )   PDF (2013KB) ( 92 )   We mainly investigate the rational solutions and N-wave resonance solutions for the (3+1)-dimensional Kudryashov-Sinelshchikov equation, which could be used to describe the liquid containing gas bubbles. With appropriate transformations, two kinds of bilinear forms are derived. Employing the two bilinear equations, dynamical behaviors of nine district solutions for this equation are discussed in detail, including bright rogue wave-type solution, dark rogue wave-type solution, bright W-shaped solution, dark W-shaped rational solution, generalized rational solution and bright-fusion, dark-fusion, bright-fission, and dark-fission resonance solutions. In addition, the generalized rational solutions, which depending on two arbitrary parameters, have an interesting structure: splitting from two peaks into three peaks.
 Double-dot interferometer for quantum measurement of Majorana qubits and stabilizers Kai Zhou(周凯), Cheng Zhang(张程), Lupei Qin(秦陆培), and Xin-Qi Li(李新奇) Chin. Phys. B, 2021, 30 (1):  010301.  DOI: 10.1088/1674-1056/abc549 Abstract ( 120 )   HTML ( 1 )   PDF (1276KB) ( 90 )   Motivated by the need of quantum measurement of Majorana qubits and surface-code stabilizers, we analyze the performance of a double-dot interferometer under the influence of environment noise. The double-dot setup design allows accounting for the full multiple tunneling process between the dots through the Majorana island, within a master equation approach. In the co-tunneling regime, which results in a Majorana-mediated effective coupling between the dots, the master equation approach allows us to obtain analytic solutions for the measurement currents. The measurement quality, characterized by figures of merit such as the visibility of measurement signals, is carried out in regard to the unusual decoherence effect rather than `which-path' dephasing. The results obtained in this work are expected to be useful for future experiments of Majorana qubit and stabilizer measurements.
 Metal-insulator phase transition and topology in a three-component system Shujie Cheng(成书杰) and Xianlong Gao(高先龙) Chin. Phys. B, 2021, 30 (1):  010302.  DOI: 10.1088/1674-1056/abb305 Abstract ( 64 )   HTML ( 1 )   PDF (2430KB) ( 29 )   Due to the topology, insulators become non-trivial, particularly those with large Chern numbers which support multiple edge channels, catching our attention. In the framework of the tight binding approximation, we study a non-interacting Chern insulator model on the three-component dice lattice with real nearest-neighbor and complex next-nearest-neighbor hopping subjected to $$\Lambda$$-or V-type sublattice potentials. By analyzing the dispersions of corresponding energy bands, we find that the system undergoes a metal-insulator transition which can be modulated not only by the Fermi energy but also the tunable extra parameters. Furthermore, rich topological phases, including the ones with high Hall plateau, are uncovered by calculating the associated band's Chern number. Besides, we also analyze the edge-state spectra and discuss the correspondence between Chern numbers and the edge states by the principle of bulk-edge correspondence. In general, our results suggest that there are large Chern number phases with C= 3 and the work enriches the research about large Chern numbers in multiband systems.
 Entropy squeezing for a V-type three-level atom interacting with a single-mode field and passing through the amplitude damping channel with weak measurement Cui-Yu Zhang(张翠玉) and Mao-Fa Fang(方卯发) Chin. Phys. B, 2021, 30 (1):  010303.  DOI: 10.1088/1674-1056/abb304 Abstract ( 48 )   HTML ( 3 )   The entropy squeezing of a V-type three-level atom interacting with a single-mode field and passing through the amplitude damping channel is investigated in detail. Our results show that when coupled to the single-mode field, the atom in appropriate initial states can not only generate obvious entropy squeezing but also keep in the optimal squeezing state, while passing through the amplitude damping channel, the atom can generate entropy squeezing under the control of the weak measurement. Besides, it is proved again that as a measurement method for atomic squeezing, the entropy squeezing is precise and effective. Therefore our work is instructive for experiments in preparing three-level system information resource with ultra-low quantum noise.
 Steady and optimal entropy squeezing for three types of moving three-level atoms coupled with a single-mode coherent field Wen-Jin Huang(黄文进) and Mao-Fa Fang(方卯发) Chin. Phys. B, 2021, 30 (1):  010304.  DOI: 10.1088/1674-1056/abc542 Abstract ( 89 )   HTML ( 1 )   PDF (551KB) ( 65 )   The entropy squeezing properties of different types of moving three-level atoms coupled with a single-mode coherent field are studied. The influences of the moving velocity and initial states of the three-level atom on the entropy squeezing are discussed. The results show that, the entropy squeezing properties of the three-level atom depend on its initial state, moving velocity, and the type. A stationary three-level atom can not obtain a steady entropy squeezing whatever initial conditions are chosen, while a moving three-level atom can achieve a steady and optimal entropy squeezing through choosing higher velocity and appropriate initial state. Our result provides a simple method for preparing squeezing resources with ultra-low quantum noise of the three-level atomic system without additional any complex techniques.
 Enhancement of multiatom non-classical correlations and quantum state transfer in atom-cavity-fiber system Qi-Liang He(贺启亮), Jian Sun(孙剑), Xiao-Shu Song(宋晓书), and Yong-Jun Xiao(肖勇军) Chin. Phys. B, 2021, 30 (1):  010305.  DOI: 10.1088/1674-1056/abb7f4 Abstract ( 104 )   HTML ( 2 )   PDF (634KB) ( 39 )   Taking the advantage of "parity kicks" pulses, we investigate the non-classical correlation dynamics and quantum state transfer in an atom-cavity-fiber system, which consists of two identical subsystems, each subsystem comprising of multiple two-level atoms trapped in two remote single-model optical cavities that are linked by an optical fiber. It is found that the non-classical correlations and the fidelity of quantum state transfer (between the atoms) can be greatly improved by the parity kicks pulses. In particular, with decrease of the time intervals between two consecutive pulses, perfect non-classical correlation transfer and entangled state transfer can be achieved.
 Painlevé property, local and nonlocal symmetries, and symmetry reductions for a (2+1)-dimensional integrable KdV equation Xiao-Bo Wang(王晓波), Man Jia(贾曼), and Sen-Yue Lou(楼森岳) Chin. Phys. B, 2021, 30 (1):  010501.  DOI: 10.1088/1674-1056/010501 Abstract ( 135 )   PDF (433KB) ( 94 )   The Painlevé property for a (2+1)-dimensional Korteweg-de Vries (KdV) extension, the combined KP3 (Kadomtsev-Petviashvili) and KP4 (cKP3-4), is proved by using Kruskal's simplification. The truncated Painlevé expansion is used to find the Schwartz form, the B\"acklund/Levi transformations, and the residual nonlocal symmetry. The residual symmetry is localized to find its finite B\"acklund transformation. The local point symmetries of the model constitute a centerless Kac-Moody-Virasoro algebra. The local point symmetries are used to find the related group-invariant reductions including a new Lax integrable model with a fourth-order spectral problem. The finite transformation theorem or the Lie point symmetry group is obtained by using a direct method.
 Interaction properties of solitons for a couple of nonlinear evolution equations Syed Tahir Raza Rizvi, Ishrat Bibi, Muhammad Younis, and Ahmet Bekir Chin. Phys. B, 2021, 30 (1):  010502.  DOI: 10.1088/1674-1056/abaed3 Abstract ( 87 )   HTML ( 1 )   PDF (1498KB) ( 71 )   We study one-and two-soliton solutions for the Cahn-Allen (CA) equation and the Brethorton equation. The CA equation has broad spectrum of applications especially in anti-phase boundary motion and it is used in phase-field models. While the Brethorton equation is a model for dispersive wave systems, it is used to find the resonant nonlinear interaction among three linear modes. We use the Hirota bilinear method to obtain one-and two-soliton solutions to the CA equation and the Brethorton equation.
 Stable water droplets on composite structures formed by embedded water into fully hydroxylated β-cristobalite silica Hanqi Gong(龚菡琪), Chonghai Qi(齐崇海), Junwei Yang(杨俊伟), Jige Chen(陈济舸), Xiaoling Lei(雷晓玲), Liang Zhao(赵亮), and Chunlei Wang(王春雷) Chin. Phys. B, 2021, 30 (1):  010503.  DOI: 10.1088/1674-1056/abc2b7 Abstract ( 158 )   HTML ( 1 )   PDF (1271KB) ( 95 )   Using molecular dynamics simulations, we have revealed a novel wetting phenomenon with a droplet on composite structures formed by embedded water into (111) surface of β-cristobalite hydroxylated silica. This can be attributed to the formation of a composite structure composed of embedded water molecules and the surface hydroxyl (-OH) groups, which reduces the number of hydrogen bonds between the composite structure and the water droplet above the composite structure. Interestingly, a small uniform strain ( 3%) applied to the crystal lattice of the hydroxylated silica surface can result in a notable change of the contact angles (>40°) on the surface. The finding provides new insights into the correlation between the molecular-scale interfacial water structures and the macroscopic wettability of the hydroxylated silica surface.
 Synchronization mechanism of clapping rhythms in mutual interacting individuals Shi-Lan Su(苏世兰), Jing-Hua Xiao(肖井华), Wei-Qing Liu(刘维清), and Ye Wu(吴晔) Chin. Phys. B, 2021, 30 (1):  010505.  DOI: 10.1088/1674-1056/abb30a Abstract ( 84 )   HTML ( 1 )   PDF (611KB) ( 45 )   In recent years, clapping synchronization between individuals has been widely studied as one of the typical synchronization phenomena. In this paper, we aim to reveal the synchronization mechanism of clapping interactions by observing two individuals' clapping rhythms in a series of experiments. We find that the two synchronizing clapping rhythm series exhibit long-range cross-correlations (LRCCs); that is, the interaction of clapping rhythms can be seen as a strong-anticipation process. Previous studies have demonstrated that the interactions in local timescales or global matching in statistical structures of fluctuation in long timescales can be sources of the strong-anticipation process. However, the origin of the strong anticipation process often appears elusive in many complex systems. Here, we find that the clapping synchronization process may result from the local interaction between two clapping individuals and may result from the more global coordination between two clapping individuals. We introduce two stochastic models for mutually interacting clapping individuals that generate the LRCCs and prove theoretically that the generation of clapping synchronization process needs to consider both local interaction and global matching. This study provides a statistical framework for studying the internal synchronization mechanism of other complex systems. Our theoretical model can also be applied to study the dynamics of other complex systems with the LRCCs, including finance, transportation, and climate.
ATOMIC AND MOLECULAR PHYSICS
 Ultrafast photoionization of ions and molecules by orthogonally polarized intense laser pulses: Effects of the time delay Si-Qi Zhang(张思琪), Zhi-Jie Yang(杨志杰), Zhi-Xian Lei(雷志仙), Wei Feng(冯伟), Sheng-Peng Zhou(周胜鹏), Kai-Jun Yuan(元凯军), Xue-Shen Liu(刘学深), and Jing Guo(郭静) Chin. Phys. B, 2021, 30 (1):  013201.  DOI: 10.1088/1674-1056/abb30c Abstract ( 159 )   HTML ( 2 )   PDF (3074KB) ( 119 )   We present the photoelectron momentum distributions (PMDs) and the photoelectron angular distributions (PADs) of He+ ions, aligned H2+ molecules and N2 molecules by intense orthogonally polarized laser pulses. Simulations are performed by numerically solving the corresponding two-dimensional time-dependent Schrödinger equations (TDSEs) within the single-electron approximation frame. Photoelectron momentum distributions and photoelectron angular distributions present different patterns with the time delays T d, illustrating the dependences of the PMDs and PADs on the time delays by orthogonally polarized laser pulses. The evolution of the electron wavepackets can be employed to describe the intensity of the PADs from the TDSE simulations for N2 molecules.
 Probing time delay of strong-field resonant above-threshold ionization Shengliang Xu(徐胜亮), Qingbin Zhang(张庆斌), Cheng Ran(冉成), Xiang Huang(黄湘), Wei Cao(曹伟), and Peixiang Lu(陆培祥) Chin. Phys. B, 2021, 30 (1):  013202.  DOI: 10.1088/1674-1056/abc7a5 Abstract ( 119 )   HTML ( 1 )   PDF (815KB) ( 68 )   The high-resolution three-dimensional photoelectron momentum distributions via above-threshold ionization (ATI) of Xe atoms are measured in an intense near circularly polarized laser field using velocity map imaging and tomography reconstruction. Compared to the linearly polarized laser field, the employed near circularly polarized laser field imposes a more strict selection rule for the transition via resonant excitation, and therefore we can selectively enhance the resonant ATI through certain atomic Rydberg states. Our results show the self-reference ionization delay, which is determined from the difference between the measured streaking angles for nonadiabatic ATI via the 4f and 5f Rydberg states, is 45.6 as. Our method provides an accessible route to highlight the role of resonant transition between selected states, which will pave the way for fully understanding the ionization dynamics toward manipulating electron motion as well as reaction in an ultrafast time scale.
 R-branch high-lying transition emission spectra of SbNa molecule Chun-Run Luo(罗春润), Qun-Chao Fan(樊群超), Zhi-Xiang Fan(范志祥), Jia Fu(付佳), Jie Ma(马杰), Hui-Dong Li(李会东), and Yong-Gen Xu(徐勇根) Chin. Phys. B, 2021, 30 (1):  013301.  DOI: 10.1088/1674-1056/abc3b2 Abstract ( 108 )   HTML ( 2 )   PDF (1083KB) ( 48 )   The calculation results of the R-branch transition emission spectra of (0-0) band of the $$A_2 1\to X_2 1$$ transition system of SbNa molecule are presented in this paper. These R-branch high-lying transitional emission spectral lines are predicted by using the difference converging method (DCM). Our results show excellent agreement between DCM spectral lines and the experimental values, and the deviations are controlled within 0.0224 cm-1. What is more, based on the principle of over-determined linear equations, the prediction error is quantified in this work, which provides reliable theoretical support for our predicted DCM calculations. This work provides a lot of useful information for understanding the microstructure of SbNa molecule.
ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
 Broadband asymmetric transmission for linearly and circularly polarization based on sand-clock structured metamaterial Tao Fu(傅涛), Xing-Xing Liu(刘兴兴), Guo-Hua Wen(文国华), Tang-You Sun(孙堂友), Gong-Li Xiao(肖功利), and Hai-Ou Li(李海鸥) Chin. Phys. B, 2021, 30 (1):  014201.  DOI: 10.1088/1674-1056/abb662 Abstract ( 116 )   HTML ( 2 )   PDF (1583KB) ( 49 )   We proposed a sandwich structure to realize broadband asymmetric transmission (AT) for both linearly and circularly polarized waves in the near infrared spectral region. The structure composes of a silica substrate and two sand-clock-like gold layers on the opposite sides of the substrate. Due to the surface plasmons of gold, the structure shows that the AT parameters of linearly and circularly polarized waves can reach 0.436 and 0.403, respectively. Meanwhile, a broadband property is presented for the AT parameter is over 0.3 between 320 THz and 340 THz. The structure realizes a diode-like AT for linearly wave in forward and circularly wave in backward, respectively. The magnetic dipoles excited by current in the two gold layers contribute to the broadband AT. The current density in top and bottom metallic layers illustrates the mechanism of the polarization conversion for broadband AT in detail.
 Tunable dual-band terahertz graphene absorber with guided mode resonances Jun Wu(吴俊), Xia-Yin Liu(刘夏吟), and Zhe Huang(黄喆) Chin. Phys. B, 2021, 30 (1):  014202.  DOI: 10.1088/1674-1056/abaee2 Abstract ( 69 )   HTML ( 2 )   PDF (622KB) ( 55 )   A tunable dual-band terahertz absorber is designed and investigated. The unit cell of the proposed absorber consists of a graphene monolayer on a guided-mode resonant filter. The graphene absorber presents >40% absorption at two resonance frequencies, which is attributed to the guided mode resonances with different mode numbers. The electric field intensity distribution is analyzed to disclose the physical mechanism of such a dual-band absorption effect. Furthermore, the influence of optical properties of graphene, including Fermi level and relaxation time, on the absorption spectra are investigated. Finally, the influence of geometric parameters on the absorption spectrum is studied, which will provide useful guidance for the fabrication of this absorber. We believe that the results may be useful for developing the next-generation graphene-based optoelectronic devices.
 Random-injection-based two-channel chaos with enhanced bandwidth and suppressed time-delay signature by mutually coupled lasers: Proposal and numerical analysis Shi-Rong Xu(许世蓉), Xin-Hong Jia (贾新鸿), Hui-Liang Ma(马辉亮), Jia-Bing Lin(林佳兵), Wen-Yan Liang(梁文燕), and Yu-Lian Yang(杨玉莲) Chin. Phys. B, 2021, 30 (1):  014203.  DOI: 10.1088/1674-1056/abb228 Abstract ( 65 )   HTML ( 1 )   PDF (4746KB) ( 80 )   Simultaneous bandwidth (BW) enhancement and time-delay signature (TDS) suppression of chaotic lasing over a wide range of parameters by mutually coupled semiconductor lasers (MCSLs) with random optical injection are proposed and numerically investigated. The influences of system parameters on TDS suppression (characterized by autocorrelation function (ACF) and permutation entropy (PE) around characteristic time) and chaos BW are investigated. The results show that, with the increasing bias current, the ranges of parameters (detuning and injection strength) for the larger BW (> 20 GHz) are broadened considerably, while the parameter range for optimized TDS (< 0.1) is not shrunk obviously. Under optimized parameters, the system can simultaneously achieve two chaos outputs with enhanced BW (>20 GHz) and perfect TDS suppression. In addition, the system can generate two-channel high-speed truly physical random number sequences at 200 Gbits/s for each channel.
 Nonparaxial propagation of radially polarized chirped Airy beams in uniaxial crystal orthogonal to the optical axis Yaohui Chen(陈耀辉), Lixun Wu(吴理汛), Zhixiong Mo(莫智雄), Lican Wu(吴利灿), and Dongmei Deng(邓冬梅) Chin. Phys. B, 2021, 30 (1):  014204.  DOI: 10.1088/1674-1056/abb226 Abstract ( 76 )   HTML ( 1 )   PDF (3177KB) ( 36 )   The nonparaxial propagation of radially polarized chirped Airy beams (RPCAiBs) in uniaxial crystal orthogonal to the optical axis is analytically studied. The effects of the first and the second order chirp factors, and the ratio of the extraordinary refractive index to the ordinary refractive index on the nonparaxial evolution of RPCAiBs in different observation planes are investigated in detail. The results show that when one parameter changes, different components behave differently, and even the same component has various behavior in different directions. The initial slope of RPCAiBs in the x-direction varies more with the first order chirp factor than that in the y-direction. Meanwhile, with the second order chirp factor becoming larger, the depth of the focus of the y-component in the x-direction decreases while that in the y-direction has no difference. In addition, the different ratios of the extraordinary refractive index to the ordinary refractive index change the difference of the depth of the focus between the x-and the y-components.
 Broadband and efficient second harmonic generation in LiNbO3-LiTaO3 composite ridge waveguides at telecom-band Xin-Tong Zhang(张欣桐) Chin. Phys. B, 2021, 30 (1):  014205.  DOI: 10.1088/1674-1056/abb232 Abstract ( 65 )   HTML ( 2 )   PDF (877KB) ( 23 )   Broadband nonlinear frequency conversions of optical waves are widely employed in multiple areas of optics and photonics. However, the broadening of conversion bandwidth is often at a cost of reduction in efficiency, which may induce a limitation on practical applications. Here we theoretically propose a novel design of LiNbO3 ridge waveguides on LiTaO3 substrates which can be used for efficient and broadband second harmonic generation. Through group velocity engineering of the ridge waveguides, acceptance bandwidth over 20 nm with a high conversion efficiency of >25%W -1cm -2 is achieved at telecom-band.
 Suppression of multi-pulse formation in all-polarization-maintaining figure-9 erbium-doped fiber mode-locked laser Jun-Kai Shi(石俊凯), Deng-Feng Dong(董登峰), Ying-Ling Pan(潘映伶), Guan-Nan Li(李冠楠), Yao Li(黎尧), Li-Tuo Liu(刘立拓), Xiao-Mei Chen(陈晓梅), and Wei-Hu Zhou(周维虎) Chin. Phys. B, 2021, 30 (1):  014206.  DOI: 10.1088/1674-1056/abc153 Abstract ( 110 )   HTML ( 2 )   PDF (1088KB) ( 69 )   We report on a novel architecture to suppress the multi-pulse formation in an all-polarization-maintaining figure-9 erbium-doped fiber laser under high pump power. A 2× 2 fiber coupler is introduced into the phase-biased nonlinear amplifying loop mirror to extract part of intracavity laser power as a laser output, and the dependence of output couple ratio of fiber coupler on the mode-locking state is experimentally investigated. The intracavity nonlinear effect is mitigated by lowering the intracavity laser power, which is conducive to avoiding the multi-pulse formation. In the meantime, the loss-imbalance induced by fiber coupler is helpful in improving the self-starting ability. With the proposed laser structure, the multiple pulse formation can be suppressed and high power single pulse train can be obtained. The laser emits three pulse trains which is convenient for some applications. Finally, the output power values of three ports are 5.3 mW, 51.3 mW, and 13.2 mW, respectively. The total single pulse output power is 69.8 mW, which is more than 10 times the result without OC2. The total slope efficiency is about 10.1%. The repetition rate of three pulse trains is 21.17 MHz, and the pulse widths are 2.8 ps, 2.63 ps, and 6.66 ps, respectively.
 Plasmonic characteristics of suspended graphene-coated wedge porous silicon nanowires with Ag partition Xu Wang(王旭), Jue Wang(王珏), Tao Ma(马涛), Heng Liu(刘恒), and Fang Wang(王芳) Chin. Phys. B, 2021, 30 (1):  014207.  DOI: 10.1088/1674-1056/abb65c Abstract ( 55 )   HTML ( 1 )   PDF (1240KB) ( 26 )   We investigate a graphene-coated nanowire waveguide (GCNW) composed of two suspended wedge porous silicon nanowires and a thin Ag partition. The plasmonic characteristics of the proposed structure in terahertz (THz) frequency band are simulated by the finite element method (FEM). The parameters including the gap between the nanowires and Ag partition, the height of the nanowire, the thickness of the Ag partition, and the Fermi level of graphene, are optimized. The simulation results show that a normalized mode field area of ∼ 10 -4 and a figure of merit of ∼ 100 can be achieved. Compared with the cylindrical GCNW and isolated GCNW, the proposed wedge GCNW has good electric field enhancement. A waveguide sensitivity of 32.28 is obtained, which indicates the prospects of application in refractive index (RI) sensing in THz frequency band. Due to the adjustable plasmonic characteristics by changing the Fermi level (E F), the proposed structure has promising applications in the electro-optic modulations, optical interconnects, and optical switches.
 Compressive imaging based on multi-scale modulation and reconstruction in spatial frequency domain Fan Liu(刘璠), Xue-Feng Liu(刘雪峰), Ruo-Ming Lan(蓝若明), Xu-Ri Yao(姚旭日), Shen-Cheng Dou(窦申成), Xiao-Qing Wang(王小庆), and Guang-Jie Zhai(翟光杰) Chin. Phys. B, 2021, 30 (1):  014208.  DOI: 10.1088/1674-1056/abb3ea Abstract ( 125 )   HTML ( 1 )   PDF (1717KB) ( 66 )   Imaging quality is a critical component of compressive imaging in real applications. In this study, we propose a compressive imaging method based on multi-scale modulation and reconstruction in the spatial frequency domain. Theoretical analysis and simulation show the relation between the measurement matrix resolution and compressive sensing (CS) imaging quality. The matrix design is improved to provide multi-scale modulations, followed by individual reconstruction of images of different spatial frequencies. Compared with traditional single-scale CS imaging, the multi-scale method provides high quality imaging in both high and low frequencies, and effectively decreases the overall reconstruction error. Experimental results confirm the feasibility of this technique, especially at low sampling rate. The method may thus be helpful in promoting the implementation of compressive imaging in real applications.
 Controlling the light wavefront through a scattering medium based on direct digital frequency synthesis technology Yuan Yuan(袁园), Min-Yuan Sun(孙敏远), Yong Bi(毕勇), Wei-Nan Gao(高伟男), Shuo Zhang(张硕), and Wen-Ping Zhang(张文平) Chin. Phys. B, 2021, 30 (1):  014209.  DOI: 10.1088/1674-1056/abb665 Abstract ( 90 )   HTML ( 1 )   PDF (1169KB) ( 48 )   Phase modulation is a crucial step when the frequency-based wavefront optimization technique is exploited to measure the optical transmission matrix (TM) of a scattering medium. We report a simple but powerful method, direct digital frequency synthesis (DDS) technology to modulate the phase front of the laser and measure the TM. By judiciously modulating the phase front of a He-Ne laser beam, we experimentally generate a high quality focus at any targeted location through a 2 mm thick 120 grit ground glass diffuser, which is commercially used in laser display and laser holographic display for improving brightness uniformity and reducing speckle. The signal to noise ratio (SNR) of the clear round focus is ∼ 50 and the size is about 44 μ m. Our study will open up new avenues for enhancing light energy delivery to the optical engine in laser TV to lower the power consumption, phase compensation to reduce the speckle noise, and controlling the lasing threshold in random lasers.
 Shear-horizontal transverse-electric seismoelectric waves in cylindrical double layer porous media Wei-Hao Wang(王伟豪), Xiao-Yan Zhu(朱晓焱), Jin-Xia Liu(刘金霞), and Zhi-Wen Cui(崔志文) Chin. Phys. B, 2021, 30 (1):  014301.  DOI: 10.1088/1674-1056/abb308 Abstract ( 71 )   HTML ( 1 )   PDF (1112KB) ( 36 )   The shear-horizontal (SH) waves excited by the shear source in a borehole are easy to analyze due to the simple waveform. The borehole-side structures make the formation properties discontinuous. We consider a cylindrical double layer structure and study the borehole shear-horizontal and transverse-electric (SH-TE) seismoelectric waves. We first derive the expressions of the basic field quantities, and simulate the acoustic field and electric field using the real axis integral method. Compared with the wave fields of an infinitely homogeneous porous medium outside the borehole, the cylindrical layered structure makes the multi-mode cylindrical Love waves and their accompanying electric fields excited. Next, in order to study the interface response law of the inducing electric fields, we use the secant integral method to calculate the interface converted electromagnetic waves and analyze the causes of each component. It is found that an interface response occurs each time the SH wave impinges the interface in the layered porous medium. The results show that the SH-TE mode has a potential application for borehole-side interface detection in geophysical logs.
 High-resolution bone microstructure imaging based on ultrasonic frequency-domain full-waveform inversion Hot! Yifang Li(李义方), Qinzhen Shi(石勤振), Ying Li(李颖), Xiaojun Song(宋小军), Chengcheng Liu(刘成成), Dean Ta(他得安), and Weiqi Wang(王威琪) Chin. Phys. B, 2021, 30 (1):  014302.  DOI: 10.1088/1674-1056/abc7aa Abstract ( 433 )   HTML ( 1 )   PDF (9210KB) ( 802 )   The main challenge in bone ultrasound imaging is the large acoustic impedance contrast and sound velocity differences between the bone and surrounding soft tissue. It is difficult for conventional pulse-echo modalities to give accurate ultrasound images for irregular bone boundaries and microstructures using uniform sound velocity assumption rather than getting a prior knowledge of sound speed. To overcome these limitations, this paper proposed a frequency-domain full-waveform inversion (FDFWI) algorithm for bone quantitative imaging utilizing ultrasonic computed tomography (USCT). The forward model was calculated in the frequency domain by solving the full-wave equation. The inverse problem was solved iteratively from low to high discrete frequency components via minimizing a cost function between the modeled and measured data. A quasi-Newton method called the limited-memory Broyden-Fletcher-Goldfarb-Shanno algorithm (L-BFGS) was utilized in the optimization process. Then, bone images were obtained based on the estimation of the velocity and density. The performance of the proposed method was verified by numerical examples, from tubular bone phantom to single distal fibula model, and finally with a distal tibia-fibula pair model. Compared with the high-resolution peripheral quantitative computed tomography (HR-pQCT), the proposed FDFWI can also clearly and accurately presented the wavelength scaled pores and trabeculae in bone images. The results proved that the FDFWI is capable of reconstructing high-resolution ultrasound bone images with sub-millimeter resolution. The parametric bone images may have the potential for the diagnosis of bone disease.
 Numerical simulation on ionic wind in circular channels Gui-Wen Zhang(张桂文), Jue-Kuan Yang(杨决宽), and Xiao-Hui Lin(林晓辉) Chin. Phys. B, 2021, 30 (1):  014701.  DOI: 10.1088/1674-1056/abb3f4 Abstract ( 62 )   HTML ( 2 )   PDF (2398KB) ( 31 )   Ionic wind induced by direct-current corona discharge has attracted considerable interest because of its low energy consumption, low noise emission, flexible designs, and lack of moving parts. The purpose of this study is to investigate the configuration parameters to improve the velocity of the ionic wind. Accordingly, this study develops a three-dimensional (3D) model of circular tube with multi-needle-to-mesh electrode configurations, in this model, the influences of various parameters were explored，such as the mesh gap, the distribution of needle electrodes, the number of needle electrodes, and the radius of the circular channel. The numerical research results showed that the mesh gap, the distribution of needle electrodes, and the radius of the circular tube significantly affected the velocity of the ionic wind. When mesh gap is 12 mm, which indicates that there is an optimal mesh gap which can enhance the velocity of the ionic wind. What is more, changing the distribution of needle electrodes and increasing the number of needle electrodes can effectively improve the velocity of the ionic wind, the optimum distribution α of needle electrodes is 0.7-0.9, which greatly increase the velocity of the ionic wind. However, for multi-needle-to-mesh structure, the improvement of the radius of the circular channel is conducive to enhance the velocity and improve the velocity distribution.
 Effect of high-or low-speed fluctuations on the small-scale bursting events in an active control experiment Xiao-Tong Cui(崔晓通), Nan Jiang(姜楠), and Zhan-Qi Tang(唐湛棋) Chin. Phys. B, 2021, 30 (1):  014702.  DOI: 10.1088/1674-1056/abc7a9 Abstract ( 69 )   HTML ( 2 )   PDF (2086KB) ( 34 )   Active control of a fully developed turbulence boundary layer (TBL) over a flat plate has been investigated with a statistical view. The piezoelectric (PZT) oscillator is employed to produce periodic input into the inner region of the TBL. A wall probe is fixed upstream of the oscillator to identify the high-or low-speed fluctuations as the detecting signals. Then, the impact of the detecting signals on the small-scale bursting process is investigated based on the data acquired by the traversing probe downstream of the oscillator. The results indicate that the small-scale bursting intensity is restrained more apparently at high-speed detecting fluctuations but less impacted at low-speed detecting fluctuations. Furthermore, the perturbed-scale fluctuations arrange the small-scale bursting process in the near-wall region. The detecting signals have an obvious impact on this arrangement, especially the high-intensity regions of the small-scale bursting events: the vibration enhances the intensity at high-speed detecting signals but weakens it at low-speed detecting signals in these regions, which gives a direct evidence on how detecting signals interfering the small-scale bursting process.
 Effect of pressure on the electrical properties of flexible NiPc thin films fabricated by rubbing-in technology Khasan S Karimov, Fahmi F Muhammadsharif, Zubair Ahmad, M Muqeet Rehman, and Rashid Ali Chin. Phys. B, 2021, 30 (1):  014703.  DOI: 10.1088/1674-1056/abb3ec Abstract ( 64 )   HTML ( 2 )   PDF (1990KB) ( 21 )   Nickel phthalocyanine (NiPc) film was deposited onto the surface of flexible conductive glass by rubbing-in technology and used to fabricate devices based on ITO/NiPc/CNT/rubber structure. The I-V characteristics of the devices were investigated under different uniaxial pressures of 200, 280, and 480 gf/cm2, applied perpendicular to the surface of the NiPc film. Results showed that the nonlinearity coefficients of the I-V curves are in the range of 2 to 3, which was found to be decreased with the increase of the pressure. The rectification ratio of the devices was estimated to be varied from 1.5 to 3 based on the applied pressure. Concluding, the resistance of the active layers was decreased with the increase of both pressure and voltage. We believe that using the rubbing-in technology under sufficient applied pressure it is possible to utilize NiPc for the development of various electronic devices such as diodes, nonlinear resistors, and sensors.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
 Propagation dynamics of relativistic electromagnetic solitary wave as well as modulational instability in plasmas Rong-An Tang(唐荣安), Tiao-Fang Liu(刘调芳), Xue-Ren Hong(洪学仁), Ji-Ming Gao(高吉明), Rui-Jin Cheng(程瑞锦), You-Lian Zheng(郑有莲), and Ju-Kui Xue(薛具奎) Chin. Phys. B, 2021, 30 (1):  015201.  DOI: 10.1088/1674-1056/abb224 Abstract ( 78 )   HTML ( 2 )   PDF (1305KB) ( 38 )   By one-dimensional particle-in-cell (PIC) simulations, the propagation and stability of relativistic electromagnetic (EM) solitary waves as well as modulational instability of plane EM waves are studied in uniform cold electron-ion plasmas. The investigation not only confirms the solitary wave motion characteristics and modulational instability theory, but more importantly, gives the following findings. For a simulation with the plasma density 1023 m-3 and the dimensionless vector potential amplitude 0.18, it is found that the EM solitary wave can stably propagate when the carrier wave frequency is smaller than 3.83 times of the plasma frequency. While for the carrier wave frequency larger than that, it can excite a very weak Langmuir oscillation, which is an order of magnitude smaller than the transverse electron momentum and may in turn modulate the EM solitary wave and cause the modulational instability, so that the solitary wave begins to deform after a long enough distance propagation. The stable propagation distance before an obvious observation of instability increases (decreases) with the increase of the carrier wave frequency (vector potential amplitude). The study on the plane EM wave shows that a modulational instability may occur and its wavenumber is approximately equal to the modulational wavenumber by Langmuir oscillation and is independent of the carrier wave frequency and the vector potential amplitude. This reveals the role of the Langmuir oscillation excitation in the inducement of modulational instability and also proves the modulational instability of EM solitary wave.
 A fitting formula for electron-ion energy partition fraction of 3.54-MeV fusion alpha particles in hot dense deuterium-tritium plasmas Yan-Ning Zhang(张艳宁), Zhi-Gang Wang(王志刚), Yong-Tao Zhao(赵永涛), and Bin He(何斌) Chin. Phys. B, 2021, 30 (1):  015202.  DOI: 10.1088/1674-1056/abc53b Abstract ( 92 )   HTML ( 2 )   PDF (1964KB) ( 47 )   Based on our previous work (Phys. Plasmas 25 012704 (2018)), a fitting formula is given for electron-ion energy partition fraction of 3.54-MeV fusion alpha particles in deuterium-tritium (DT) plasmas as a function of plasma mass density ρ , electron temperature T e , and ion temperature T i. The formula can be used in a huge range of the plasma state, where ρ varies between 1.0 g/cc∼ 10.03 g/cc and both T e and T i change from 0.1 keV to 100.0 keV. Relativistic effect for electrons is investigated including the effect of the projectile recoil in the plasmas at T e ≥ 50.0 keV. The partition fraction for T e>T i is found to be close to that for T e=T i. The comparisons with other fitting results are made at some plasma densities when T e=T i, and the difference is explained. The fitting result is very close to the calculated one in most cases, which is convenient for the simulation of alpha heating in hot dense DT plasmas for inertial confined fusion.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
 Ab initio study on crystal structure and phase stability of ZrC2 under high pressure Yong-Liang Guo(郭永亮), Jun-Hong Wei(韦俊红), Xiao Liu(刘潇), Xue-Zhi Ke(柯学志), and Zhao-Yong Jiao(焦照勇) Chin. Phys. B, 2021, 30 (1):  016101.  DOI: 10.1088/1674-1056/abb3e7 Abstract ( 97 )   HTML ( 1 )   PDF (2400KB) ( 41 )   The structural stabilities and crystal evolution behaviors of the hyper stoichiometric compound ZrC2 (carbon rich; C/Zr > 1.0) are studied under ambient and high pressure conditions using first-principles calculations in combination with the particle-swarm optimization algorithm. Six viable structures of ZrC2 in P21/c, Cmmm, Cmc21, P42/nmc, Immm and P6/mmm symmetries are identified. These structures are dynamically stable as their phonon spectra have no imaginary modes at zero pressure or at the selected high-pressure points. Among them, the P21/c phase represents the ground state structure, whereas P21/c, P42/nmc, Immm and P6/mmm phases are part of the phase transition series. The phase order and critical pressures of the phase transition are determined to be approximately 300 GPa according to the equation of states and enthalpy. Furthermore, the mechanical and electronic properties are investigated. The P21/c and Cmc21 phases display a semi-metal nature, whereas the P42/nmc, Immm, P6/mmm and Cmmm phases exhibit a metallic nature. Moreover, the present study reveals considerable information regarding the structural, mechanical and electronic properties of ZrC2, thereby providing key insights into its material properties and evaluating its behavior in practical applications.
 Thermal stress reduction of GaAs epitaxial growth on V-groove patterned Si substrates Ze-Yuan Yang(杨泽园), Jun Wang(王俊), Guo-Feng Wu(武国峰), Yong-Qing Huang(黄永清), Xiao-Min Ren(任晓敏), Hai-Ming Ji(季海铭), and Shuai Luo(罗帅) Chin. Phys. B, 2021, 30 (1):  016102.  DOI: 10.1088/1674-1056/abb3ed Abstract ( 104 )   HTML ( 1 )   PDF (755KB) ( 27 )   We investigate the thermal stresses for GaAs layers grown on V-groove patterned Si substrates by the finite-element method. The results show that the thermal stress distribution near the interface in a patterned substrate is nonuniform, which is far different from that in a planar substrate. Comparing with the planar substrate, the thermal stress is significantly reduced for the GaAs layer on the patterned substrate. The effects of the width of the V-groove, the thickness, and the width of the SiO2 mask on the thermal stress are studied. It is found that the SiO2 mask and V-groove play a crucial role in the stress of the GaAs layer on Si substrate. The results indicate that when the width of V-groove is 50 nm, the width and the thickness of the SiO2 mask are both 100 nm, the GaAs layer is subjected to the minimum stress. Furthermore, Comparing with the planar substrate, the average stress of the GaAs epitaxial layer in the growth window region of the patterned substrate is reduced by 90%. These findings are useful in the optimal designing of growing high-quality GaAs films on patterned Si substrates.
 TiOx-based self-rectifying memory device for crossbar WORM memory array applications Li-Ping Fu(傅丽萍), Xiao-Qiang Song(宋小强), Xiao-Ping Gao(高晓平), Ze-Wei Wu(吴泽伟), Si-Kai Chen(陈思凯), and Ying-Tao Li(李颖弢) Chin. Phys. B, 2021, 30 (1):  016103.  DOI: 10.1088/1674-1056/abc548 Abstract ( 85 )   HTML ( 1 )   PDF (665KB) ( 57 )   Resistive switching with a self-rectifying feature is one of the most effective solutions to overcome the crosstalk issue in a crossbar array. In this paper, a memory device based on Pt/TiOx/W structure with self-rectifying property is demonstrated for write-once-read-many-times (WORM) memory application. After programming, the devices exhibit excellent uniformity and keep in the low resistance state (LRS) permanently with a rectification ratio as high as 104 at 1 V. The self-rectifying resistive switching behavior can be attributed to the Ohmic contact at TiOx/W interface and the Schottky contact at Pt/TiOx interface. The results in this paper demonstrate the potential application of TiOx-based WORM memory device in crossbar arrays.
 Exciton emissions of CdS nanowire array fabricated on Cd foil by the solvothermal method Yong Li(李勇), Peng-Fei Ji(姬鹏飞), Ya-Juan Hao(郝亚娟), Yue-Li Song(宋月丽), Feng-Qun Zhou(周丰群), and Shu-Qing Yuan(袁书卿) Chin. Phys. B, 2021, 30 (1):  016104.  DOI: 10.1088/1674-1056/abbbf1 Abstract ( 84 )   HTML ( 2 )   PDF (1312KB) ( 25 )   Nanowires have recently attracted more attention because of their low-dimensional structure, tunable optical and electrical properties for next-generation nanoscale optoelectronic devices. CdS nanowire array, which is (002)-orientation growth and approximately perpendicular to Cd foil substrate, has been fabricated by the solvothermal method. In the temperature-dependent photoluminescence, from short wavelength to long wavelength, four peaks can be ascribed to the emissions from the bandgap, the transition from the holes being bound to the donors or the electrons being bound to the acceptors, the transition from Cd interstitials to Cd vacancies, and the transition from S vacancies to the valence band, respectively. In the photoluminescence of 10 K, the emission originated from the bandgap appears in the form of multiple peaks. Two stronger peaks and five weaker peaks can be observed. The energy differences of the adjacent peaks are close to 38 meV, which is ascribed to the LO phonon energy of CdS. For the multiple peaks of bandgap emission, from low energy to high energy, the first, second, and third peaks are contributed to the third-order, second-order, and first-order phonon replica of the free exciton A, respectively; the fourth peak is originated from the free exciton A; the fifth peak is contributed to the first-order phonon replica of the excitons bound to neutral donors; the sixth and seventh peaks are originated from the excitons bound to neutral donors and the light polarization parallel to the c axis of hexagonal CdS, respectively.
 Dynamic crossover in [VIO2+][Tf2N-]2 ionic liquid Gan Ren(任淦) Chin. Phys. B, 2021, 30 (1):  016105.  DOI: 10.1088/1674-1056/abb668 Abstract ( 56 )   HTML ( 1 )   PDF (601KB) ( 21 )   Ionic liquids usually behave as fragile liquids, and the temperature dependence of their dynamic properties obeys supper-Arrhenius law. In this work, a dynamic crossover is observed in ([VIO2+][Tf2N-]2) ionic liquid at the temperature of 240-800 K. The diffusion coefficient does not obey a single Arrhenius law or a Vogel-Fulcher-Tammann (VFT) relation, but can be well fitted by three Arrhenius laws or a combination of a VFT relation and an Arrhenius law. The origin of the dynamic crossover is analyzed from correlation, structure, and thermodynamics. Ion gets a stronger backward correlation at a lower temperature, as shown by the fractal dimension of the random walk. The temperature dependence function of fractal dimension, heterogeneity order parameter, and thermodynamic data can be separated into three regions similar to that observed in the diffusion coefficient. The two crossover temperatures observed in the three types of data are almost the same as that in diffusion coefficient fitted by three Arrhenius laws. The results indicate that the dynamic crossover of [VIO2+][Tf2N-]2 is attributed to the heterogeneous structure when it undergoes cooling.
 Experimental investigation of electrode cycle performance and electrochemical kinetic performance under stress loading Zi-Han Liu(刘子涵), Yi-Lan Kang(亢一澜), Hai-Bin Song(宋海滨), Qian Zhang(张茜), and Hai-Mei Xie(谢海妹) Chin. Phys. B, 2021, 30 (1):  016201.  DOI: 10.1088/1674-1056/abb30e Abstract ( 66 )   HTML ( 2 )   PDF (2106KB) ( 37 )   Lithium-ion batteries suffer from mechano-electrochemical coupling problems that directly determine the battery life. In this paper, we investigate the electrode electrochemical performance under stress conditions, where seven tensile/compressive stresses are designed and loaded on electrodes, thereby decoupling mechanics and electrochemistry through incremental stress loads. Four types of multi-group electrochemical tests under tensile/compressive stress loading and normal package loading are performed to quantitatively characterize the effects of tensile stress and compressive stress on cycle performance and the kinetic performance of a silicon composite electrode. Experiments show that a tensile stress improves the electrochemical performance of a silicon composite electrode, exhibiting increased specific capacity and capacity retention rate, reduced energy dissipation rate and impedances, enhanced reactivity, accelerated ion/electron migration and diffusion, and reduced polarization. Contrarily, a compressive stress has the opposite effect, inhibiting the electrochemical performance. The stress effect is nonlinear, and a more obvious suppression via compressive stress is observed than an enhancement via tensile stress. For example, a tensile stress of 675 kPa increases diffusion coefficient by 32.5%, while a compressive stress reduces it by 35%. Based on the experimental results, the stress regulation mechanism is analyzed. Tensile stress loads increase the pores of the electrode material microstructure, providing more deformation spaces and ion/electron transport channels. This relieves contact compressive stress, strengthens diffusion/reaction, and reduces the degree of damage and energy dissipation. Thus, the essence of stress enhancement is that it improves and optimizes diffusion, reaction and stress in the microstructure of electrode material as well as their interactions via physical morphology.
 Utilizing of high-pressure high-temperature synthesis to enhance the thermoelectric properties of Zn0.98Al0.02O with excellent electrical properties Qi Chen(陈启), Xinjian Li(李欣健), Yao Wang(王遥), Lijie Chang(常立杰), Jian Wang(王健), Yuewen Zhang(张跃文), Hongan Ma(马红安), and Xiaopeng Jia(贾晓鹏) Chin. Phys. B, 2021, 30 (1):  016202.  DOI: 10.1088/1674-1056/abc4dd Abstract ( 101 )   HTML ( 1 )   PDF (2285KB) ( 75 )   The temperature in the high-pressure high-temperature (HPHT) synthesis is optimized to enhance the thermoelectric properties of high-density ZnO ceramic, Zn0.98Al0.02O. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy show that HPHT can be utilized to control the crystal structure and relative density of the material. High pressure can be utilized to change the energy band structure of the samples via changing the lattice constant of samples, which decreases the thermal conductivity due to the formation of a multi-scale hierarchical structure and defects. The electrical conductivity of the material reaches 6× 104 S/m at 373 K, and all doped samples behave as n-type semiconductors. The highest power factor (6.42 μ W cm - 1K -2) and dimensionless figure of merit (zT=0.09) are obtained when Zn0.98Al0.02O is produced at 973 K using HPHT, which is superior to previously reported power factors for similar materials at the same temperature. Hall measurements indicate a high carrier concentration, which is the reason for the enhanced electrical performance.
 Insights into the physical properties and anisotropic nature of ErPdBi with an appearance of low minimum thermal conductivity S K Mitro, R Majumder, K M Hossain, Md Zahid Hasan, Md Emran Hossain, and M A Hadi Chin. Phys. B, 2021, 30 (1):  016203.  DOI: 10.1088/1674-1056/abaf9d Abstract ( 60 )   HTML ( 2 )   PDF (1273KB) ( 24 )   We theoretically study the structural, elastic and optical properties of ErPdBi together with its anisotropic behaviors using density functional theory. It is observed that ErPdBi satisfies the Born stability criteria nicely and possesses high quality of machinability. The anisotropic behavior of ErPdBi is reported with the help of theoretical anisotropy indices incorporating 3D graphical presentation, which suggests that ErPdBi is highly anisotropic in nature. It is noticed that the minimum thermal conductivity is very low for ErPdBi compared to the several species. This low value of minimum thermal conductivity introduces the potentiality of ErPdBi in high-temperature applications such as thermal barrier coatings. In addition, deep optical insights of ErPdBi reveal that our material can be used in different optoelectronic and electronic device applications ranging from organic light-emitting diodes, solar panel efficiency, waveguides etc. to integration of integrated circuits. Therefore, we believe that our results will provide a new insight into high-temperature applications and will benefit for the development of promising optoelectric devices as well.
 Raman scattering from highly-stressed anvil diamond Shan Liu(刘珊), Qiqi Tang(唐琦琪), Binbin Wu(吴彬彬), Feng Zhang(张峰), Jingyi Liu(刘静仪), Chunmei Fan(范春梅), and Li Lei(雷力) Chin. Phys. B, 2021, 30 (1):  016301.  DOI: 10.1088/1674-1056/abc7a7 Abstract ( 82 )   HTML ( 1 )   PDF (3026KB) ( 47 )   The high-frequency edge of the first-order Raman mode of diamond reflects the stress state at the culet of anvil, and is often used for the pressure calibration in diamond anvil cell (DAC) experiments. Here we point out that the high-frequency edge of the diamond Raman phonon corresponds to the Brillouin zone (BZ) center $$\varGamma$$ point as a function of pressure. The diamond Raman pressure gauge relies on the stability of crystal lattice of diamond under high stress. Upon the diamond anvil occurs failure under the uniaxial stress (197 GPa), the loss of intensity of the first-order Raman phonon and a stress-dependent broad Raman band centered at 600 cm - 1 are observed, which is associated with a strain-induced local mode corresponding to the BZ edge phonon of the L1 transverse acoustic phonon branch.
 Glass formation and physical properties of Sb 2S 3-CuI chalcogenide system Qilin Ye(叶旗林), Dan Chen(陈旦), and Changgui Lin(林常规) Chin. Phys. B, 2021, 30 (1):  016302.  DOI: 10.1088/1674-1056/abc0e2 Abstract ( 75 )   HTML ( 1 )   PDF (1270KB) ( 23 )   Novel chalcogenide glasses of pseudo-binary (100-x)Sb2S3-xCuI systems were synthesized by traditional melt-quenching method. The glass-forming region of Sb2S3-CuI system was determined ranging from x=30 mol% to 40 mol%. CuI acts as a non-bridging modifier to form appropriate amount of [SbSI] structural units for improving the glass-forming ability of Sb2S3. Particularly, as-prepared glassy sample is able to transmit light beyond 14 μm, which is the wider transparency region than most sulfide glasses. Their physical properties, including Vickers hardness (H v), density (ρ ), and ionic conductivity (σ ) were characterized and analyzed with the compositional-dependent Raman spectra. These experimental results would provide useful knowledge for the development of novel multi-spectral optical materials and glassy electrolytes.
 Improving robustness of complex networks by a new capacity allocation strategy Jun Liu(刘军) Chin. Phys. B, 2021, 30 (1):  016401.  DOI: 10.1088/1674-1056/abb3f1 Abstract ( 72 )   HTML ( 1 )   PDF (634KB) ( 51 )   The robustness of infrastructure networks has attracted great attention in recent years. Scholars have studied the robustness of complex networks against cascading failures from different aspects. In this paper, a new capacity allocation strategy is proposed to reduce cascading failures and improve network robustness without changing the network structure. Compared with the typical strategy proposed in Motter-Lai (ML) model, the new strategy can reduce the scale of cascading failure. The new strategy applied in scale-free network is more efficient. In addition, to reasonably evaluate the two strategies, we introduce contribution rate of unit capacity to network robustness as evaluation index. Results show that our new strategy works well, and it is more advantageous in the rational utilization of capacity in scale-free networks. Furthermore, we were surprised to find that the efficient utilization of capacity costs declined as costs rose above a certain threshold, which indicates that it is not wise to restrain cascading failures by increasing capacity costs indefinitely.
 Temperature-induced phase transition of two-dimensional semiconductor GaTe Xiaoyu Wang(王啸宇), Xue Wang(王雪), Hongshuai Zou(邹洪帅), Yuhao Fu(付钰豪), Xin He(贺欣), and Lijun Zhang(张立军) Chin. Phys. B, 2021, 30 (1):  016402.  DOI: 10.1088/1674-1056/abd394 Abstract ( 137 )   HTML ( 1 )   PDF (3175KB) ( 96 )   GaTe is a two-dimensional III-VI semiconductor with suitable direct bandgap of ∼ 1.65 eV and high photoresponsivity, which makes it a promising candidate for optoelectronic applications. GaTe exists in two crystalline phases: monoclinic (m-GaTe, with space group C2/m) and hexagonal (h-GaTe, with space group P63/mmc). The phase transition between the two phases was reported under temperature-varying conditions, such as annealing, laser irradiation, etc. The explicit phase transition temperature and energy barrier during the temperature-induced phase transition have not been explored. In this work, we present a comprehensive study of the phase transition process by using first-principles energetic and phonon calculations within the quasi-harmonic approximation framework. We predicted that the phase transition from h-GaTe to m-GaTe occurs at the temperature decreasing to 261 K. This is in qualitative agreement with the experimental observations. It is a two-step transition process with energy barriers 199 meV and 288 meV, respectively. The relatively high energy barriers demonstrate the irreversible nature of the phase transition. The electronic and phonon properties of the two phases were further investigated by comparison with available experimental and theoretical results. Our results provide insightful understanding on the process of temperature-induced phase transition of GaTe.
 Novel structures and mechanical properties of Zr2N: Ab initio description under high pressures Minru Wen(文敏儒), Xing Xie(谢兴), Zhixun Xie(谢植勋), Huafeng Dong(董华锋), Xin Zhang(张欣), Fugen Wu(吴福根), and Chong-Yu Wang(王崇愚) Chin. Phys. B, 2021, 30 (1):  016403.  DOI: 10.1088/1674-1056/abb220 Abstract ( 60 )   HTML ( 1 )   PDF (1847KB) ( 24 )   With the formation of structural vacancies, zirconium nitrides (key materials for cutting coatings, super wear-resistance, and thermal barrier coatings) display a variety of compositions and phases featuring both cation and nitrogen enrichment. This study presents a systematic exploration of the stable crystal structures of zirconium heminitride combining the evolutionary algorithm method and ab initio density functional theory calculations at pressures of 0 GPa, 30 GPa, 60 GPa, 90 GPa, 120 GPa, 150 GPa, and 200 GPa. In addition to the previously proposed phases P42/mnm-, Pnnm-, and Cmcm-Zr2N, five new high-pressure Zr2N phases of P4/nmm, I4/mcm, P21/m, $$P\bar 3 m1$$, and C2/m are discovered. An enthalpy study of these candidate configurations reveals various structural phase transformations of Zr2N under pressure. By calculating the elastic constants and phonon dispersion, the mechanical and dynamical stabilities of all predicted structures are examined at ambient and high pressures. To understand the structure-property relationships, the mechanical properties of all Zr2N compounds are investigated, including the elastic moduli, Vickers hardness, and directional dependence of Young's modulus. The Cmcm-Zr2N phase is found to belong to the brittle materials and has the highest Vickers hardness (12.9 GPa) among all candidate phases, while the I4/mcm-Zr2N phase is the most ductile and has the lowest Vickers hardness (2.1 GPa). Furthermore, the electronic mechanism underlying the diverse mechanical behaviors of Zr2N structures is discussed by analyzing the partial density of states.
 Tolman length of simple droplet: Theoretical study and molecular dynamics simulation Shu-Wen Cui(崔树稳), Jiu-An Wei(魏久安), Qiang Li(李强), Wei-Wei Liu(刘伟伟), Ping Qian(钱萍), and Xiao Song Wang(王小松) Chin. Phys. B, 2021, 30 (1):  016801.  DOI: 10.1088/1674-1056/abb65a Abstract ( 93 )   HTML ( 2 )   PDF (584KB) ( 29 )   In 1949, Tolman found the relation between the surface tension and Tolman length, which determines the dimensional effect of the surface tension. Tolman length is the difference between the equimolar surface and the surface of tension. In recent years, the magnitude, expression, and sign of the Tolman length remain an open question. An incompressible and homogeneous liquid droplet model is proposed and the approximate expression and sign for Tolman length are derived in this paper. We obtain the relation between Tolman length and the radius of the surface of tension (R s) and found that they increase with the R s decreasing. The Tolman length of plane surface tends to zero. Taking argon for example, molecular dynamics simulation is carried out by using the Lennard-Jones (LJ) potential between atoms at a temperature of 90 K. Five simulated systems are used, with numbers of argon atoms being 10140, 10935, 11760, 13500, and 15360, respectively. By methods of theoretical study and molecular dynamics simulation, we find that the calculated value of Tolman length is more than zero, and it decreases as the size is increased among the whole size range. The value of surface tension increases with the radius of the surface of tension increasing, which is consistent with Tolman's theory. These conclusions are significant for studying the size dependence of the surface tension.
 Effects of WC-Co reinforced Ni-based alloy by laser melting deposition: Wear resistance and corrosion resistance Zhao-Zhen Huang(黄昭祯), Zhi-Chen Zhang(张志臣), Fan-Liang Tantai(澹台凡亮), Hong-Fang Tian(田洪芳), Zhen-Jie Gu(顾振杰), Tao Xi(郗涛), Zhu Qian(钱铸), and Yan Fang(方艳) Chin. Phys. B, 2021, 30 (1):  016802.  DOI: 10.1088/1674-1056/abb223 Abstract ( 212 )   HTML ( 1 )   PDF (2365KB) ( 22 )   WC-Co reinforced C276 alloy composite coatings are fabricated on Q235 steel by laser melting deposition. The microstructure, hardness, wear performance, and electrochemical corrosion behavior of composite coating are studied. The results show that WC-Co particles are mostly uniformly distributed in the coating and provide favorable conditions for heterogeneous nucleation. The microstructure of C276/WC-Co composite coatings is composed of γ-Ni solid solution dendrites and MoNi solid solution eutectics. The WC-Co particles can effectively improve the hardness and wear resistance of C276 alloy. The average hardness of the composite coating containing 10-wt% WC-Co (447 HV0.2) are 1.26 times higher than that of the C276 alloy (356 HV0.2). The wear rate of composite coating containing 10-wt% WC-Co (6.95 × 10 -3 mg/m) is just 3.5% of that of C276 coating (196.23× 10 -3 mg/m). However, comparing with Hastelloy C276，the corrosion resistance of C276/WC-Co composite coating decreases.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
 Interfacial properties of g-C3N4/TiO2 heterostructures studied by DFT calculations Chen-Shan Peng(彭春山), Yong-Dong Zhou(周永东), Sui-Shuan Zhang(张虽栓), and Zong-Yan Zhao(赵宗彦) Chin. Phys. B, 2021, 30 (1):  017101.  DOI: 10.1088/1674-1056/abb30b Abstract ( 82 )   HTML ( 2 )   PDF (3097KB) ( 30 )   Constructing the hetrostructure is a feasible strategy to enhance the performances of photocatalysts. However, there are still some fundamental details and mechanisms for the specific design of photocatalysts with heterostructure, which need further confirming and explain. In this work, g-C3N4-based heterostructures are constructed with TiO2 in different ways, and their intrinsic factors to improve the photocatalytic activity are systematically studied by density functional theory (DFT). When g-C3N4 combines horizontally with TiO2 to form a heterostructure, the interaction between them is dominated by van der Waals interaction. Although the recombination of photo-generated electron-hole pair cannot be inhibited significantly, this van der Waals interaction can regulate the electronic structures of the two components, which is conducive to the participation of photo-generated electrons and holes in the photocatalytic reaction. When the g-C3N4 combines vertically with TiO2 to form a heterostructure, their interface states show obvious covalent features, which is very beneficial for the photo-generated electrons' and holes' transport along the opposite directions on both sides of the interface. Furthermore, the built-in electric field of g-C3N4/TiO2 heterostructure is directed from TiO2 layer to g-C3N4 layer under equilibrium, so the photo-generated electron-hole pairs can be spatially separated from each other. These calculated results show that no matter how g-C3N4 and TiO2 are combined together, the g-C3N4/TiO2 heterostructure can enhance the photocatalytic performance through corresponding ways.
 Structure prediction, electronic, and mechanical properties of alkali metal MB12 ( M= Be, Mg, Ca, Sr) from first principles Chun-Ying Pu(濮春英), Rong-Mei Yu(于荣梅), Ting Wang(王婷), Zhen-Yan X\"ue(薛振彦), Yong-Sheng Zhu(朱永胜), and Da-Wei Zhou(周大伟) Chin. Phys. B, 2021, 30 (1):  017102.  DOI: 10.1088/1674-1056/abb667 Abstract ( 94 )   HTML ( 1 )   PDF (1422KB) ( 51 )   Using the particle swarm optimization algorithm on structural search methods, we focus our crystal structures search on boron-rich alkali metal compounds of MB12 (M= Be, Mg, Ca, Sr) with simulation cell sizes of 1-2 formula units (f.u.) at 0 GPa. The structure, electronic, and mechanical properties of MB12 are obtained from the density functional theory using the plane-wave pseudopotential method within the generalized gradient approximations. The formation enthalpies of MB12 regarding to solid metal M and solid alpha-boron suggested the predicted structures can be synthesized except for BeB12. The calculated band structures show MB12 (M= Be, Mg, Ca, Sr) are all indirect semiconductors. All the calculated elastic constants of MB12 satisfy the the mechanical stable conditions. The mechanical parameters (i.e., bulk modulus, shear modulus, and Young's modulus) are derived using the Voigt-Reuss-Hill method. The G/B ratios indicated that the MB12 should exhibit brittle behavior. In addition, the hardness, Debye temperature, universal anisotropic index, and the percentage of anisotropy in compression and shear are also discussed in detail. We hope our results can inspire further experimental study on these boron-rich alkali-metal compounds.
 Role of Ag microalloying on glass forming ability and crystallization kinetics of ZrCoAgAlNi amorphous alloy A Surendar, K Geetha, C Rajan, and M Alaazim Chin. Phys. B, 2021, 30 (1):  017201.  DOI: 10.1088/1674-1056/abb65e Abstract ( 45 )   HTML ( 1 )   PDF (2191KB) ( 24 )   Bulk metallic glasses (BMGs) with new chemical compositions (ZrCoAgAlNi) were fabricated and the effects of Ag minor addition on the glass forming ability (GFA) and crystallization kinetics were studied. The x-ray diffraction (XRD) test was applied to identify the amorphousness of BMGs or possible crystalline phases. Using differential scanning calorimeter (DSC), the thermal stability and crystallization kinetics under a non-isothermal condition at the different heating rates were studied. Considering the heating rate dependency of glass transition and crystallization kinetics, the activation energy was evaluated and measured for the mentioned processes. It was revealed that the rise in Ag content led to the decrease in activation energy for glass transition, while the activation energy for crystallization increased. The thermal stability and GFA were also studied and it was found that the Ag addition strongly affected the inherent features of BMGs. With the increase in Ag content, the atomic mobility and structural rearrangement changed in the material and consequently, the GFA and thermal stability were significantly improved.
 Electric gating of the multichannel conduction in LaAlO3/SrTiO3 superlattices Hot! Shao-Jin Qi(齐少锦), Xuan Sun(孙璇), Xi Yan(严曦), Hui Zhang(张慧), Hong-Rui Zhang(张洪瑞), Jin-E Zhang(张金娥), Hai-Lin Huang(黄海林), Fu-Rong Han(韩福荣), Jing-Hua Song(宋京华), Bao-Gen Shen(沈保根), and Yuan-Sha Chen(陈沅沙) Chin. Phys. B, 2021, 30 (1):  017301.  DOI: 10.1088/1674-1056/abc54c Abstract ( 162 )   HTML ( 1 )   PDF (874KB) ( 132 )   The electric gating on the transport properties of two-dimensional electron gas (2DEG) at the interface of LaAlO3/SrTiO3 (LAO/STO) heterostructure has attracted great research interest due to its potential application in field-effect devices. Most of previous works of gate effect were focused on the LAO/STO heterostructure containing only one conductive interface. Here, we systematically investigated the gate effect on high-quality LAO/STO superlattices (SLs) fabricated on the TiO2-terminated (001) STO substrates. In addition to the good metallicity of all SLs, we found that there are two types of charge carriers, the majority carriers and the minority carriers, coexisting in the SLs. The sheet resistance of the SLs with a fixed thickness of the LAO layer increases monotonically as the thickness of the STO layer increases. This is derived from the dependence of the minority carrier density on the thickness of STO. Unlike the LAO/STO heterostructure in which minority and majority carriers are simultaneously modulated by the gate effect, the minority carriers in the SLs can be tuned more significantly by the electric gating while the density of majority carriers is almost invariable. Thus, we consider that the minority carriers may mainly exist in the first interface near the STO substrate that is more sensitive to the back-gate voltage, and the majority carriers exist in the post-deposited STO layers. The SL structure provides the space separation for the multichannel conduction in the 2DEG, which opens an avenue for the design of field-effect devices based on LAO/STO heterostructure.
 Self-powered solar-blind photodiodes based on EFG-grown (100)-dominant β-Ga2O3 substrate Xu-Long Chu(褚旭龙), Zeng Liu(刘增), Yu-Song Zhi(支钰崧), Yuan-Yuan Liu(刘媛媛), Shao-Hui Zhang(张少辉), Chao Wu(吴超), Ang Gao(高昂), Pei-Gang Li(李培刚), Dao-You Guo(郭道友), Zhen-Ping Wu(吴真平), and Wei-Hua Tang(唐为华) Chin. Phys. B, 2021, 30 (1):  017302.  DOI: 10.1088/1674-1056/abc546 Abstract ( 130 )   HTML ( 2 )   PDF (1207KB) ( 55 )   We report the edge-defined-film-fed (EFG)-grown β-Ga2O3-based Schottky photodiodes. The device has a reverse leakage current of ∼nA and a rectified ratio of ∼104 at $$\mathrm\pm 5$$ V. In addition, the photodiode detector shows a dark current of 0.3 pA, a photo-responsivity (R) of 2.875 mA/W, a special detectivity (D*) of 1010 Jones, and an external quantum efficiency (EQE) of 1.4% at zero bias, illustrating a self-powered operation. This work may advance the development of the Ga2O3-based Schottky diode solar-blind photodetectors.
 Optical conductivity of twisted bilayer graphene near the magic angle Lu Wen(文露), Zhiqiang Li(李志强), and Yan He(贺言) Chin. Phys. B, 2021, 30 (1):  017303.  DOI: 10.1088/1674-1056/abb65d Abstract ( 124 )   HTML ( 2 )   PDF (1136KB) ( 66 )   We theoretically study the band structure and optical conductivity of twisted bilayer graphene (TBG) near the magic angle considering the effects of lattice relaxation. We show that the optical conductivity spectrum is characterized by a series of peaks associated with the van Hove singularities in the band structure, and the peak energies evolve systematically with the twist angle. Lattice relaxation effects in TBG modify its band structure, especially the flat bands, which leads to significant shifts of the peaks in the optical conductivity. These results demonstrate that spectroscopic features in the optical conductivity can serve as fingerprints for exploring the band structure, band gap, and lattice relaxation in magic-angle TBG as well as identifying its rotation angle.
 Magnetic properties and promising cryogenic magneto-caloric performances of Gd20Ho20Tm20Cu20Ni20 amorphous ribbons Yikun Zhang(张义坤), Bingbing Wu(吴兵兵), Dan Guo(郭丹), Jiang Wang(王江), and Zhongming Ren(任忠鸣) Chin. Phys. B, 2021, 30 (1):  017501.  DOI: 10.1088/1674-1056/abc0d7 Abstract ( 95 )   HTML ( 1 )   PDF (1569KB) ( 46 )   The magnetic cooling utilizing magneto-caloric effect is recognized as promising energy efficiency and environmentally friendly technology. Here we report a systematical study on the microstructures, magnetic properties and cryogenic magneto-caloric performances of the Gd20Ho20Tm20Cu20Ni20 amorphous ribbons. It is found that the ribbons reveal a second-order phase transition and are accompanied by a table-shaped magneto-caloric effect. The calculated magnetic-entropy-change maximum |∆ S M|, temperature averaged entropy change (i.e., TEC(10)), and refrigerant capacity reach 13.9 J/kgK, 13.84 J/kgK and 740 J/kg with magnetic field change of 0-7 T, respectively, indicating that the present Gd20Ho20Tm20Cu20Ni20 amorphous ribbons are good candidates for magnetic cooling.
 Effects of dipolar interactions on the magnetic hyperthermia of Zn0.3Fe2.7O 4 nanoparticles with different sizes Xiang Yu(俞翔), Yan Mi(米岩), Li-Chen Wang(王利晨), Zheng-Rui Li(李峥睿), Di-An Wu(吴迪安), Ruo-Shui Liu(刘若水), and Shu-Li He(贺淑莉) Chin. Phys. B, 2021, 30 (1):  017503.  DOI: 10.1088/1674-1056/abb311 Abstract ( 55 )   HTML ( 1 )   PDF (873KB) ( 21 )   Tumor-targeted magnetic hyperthermia has recently attracted much attention. Magnetic nanoparticles (NPs) are heat mediator nanoprobes in magnetic hyperthermia for cancer treatment. In this paper, single cubic spinel structural Zn0.3Fe2.7O4 magnetic NPs with sizes of 14 nm-20 nm were synthesized, followed by coating with SiO2 shell. The SLP value of Zn0.3Fe2.7O4/SiO2 NPs below 20 nm changes non-monotonically with the concentration of solution under the alternating current (AC) magnetic field of 430 kHz and 27 kA/m. SLP values of all Zn0.3Fe2.7O4/SiO2 NPs appear a peak value with change of solution concentration. The solution concentrations with optimal SLP value decrease with increasing magnetic core size. This work can give guidance to the better prediction and control of the magnetic hyperthermia performance of materials in clinical applications.
 Exact soliton solutions in anisotropic ferromagnetic wires with Dzyaloshinskii-Moriya interaction Qiu-Yan Li(李秋艳), Dun-Zhao(赵敦), and Zai-Dong Li(李再东) Chin. Phys. B, 2021, 30 (1):  017504.  DOI: 10.1088/1674-1056/abca26 Abstract ( 83 )   HTML ( 1 )   PDF (13588KB) ( 97 )   We theoretically investigate the exact soliton solutions of anisotropic ferromagnetic wires with Dzyaloshinskii-Moriya interaction. For example, we give the bright and black soliton solutions. From these results we find that the Dzyaloshinskii-Moriya interaction affects the existence region of soliton, spin-wave transport, and soliton dynamic properties. As the Dzyaloshinskii-Moriya interaction grows, the soliton width is widened, which provides a way to control the soliton dynamics.
 Monolithic epitaxy and optoelectronic properties of single-crystalline γ-In2Se3 thin films on mica Xibo Yin(尹锡波), Yifan Shen(沈逸凡), Chaofan Xu(徐超凡), Jing He(贺靖), Junye Li(李俊烨), Haining Ji(姬海宁), Jianwei Wang(王建伟), Handong Li(李含冬), Xiaohong Zhu(朱小红), Xiaobin Niu(牛晓滨), and Zhiming Wang(王志明) Chin. Phys. B, 2021, 30 (1):  017701.  DOI: 10.1088/1674-1056/abcf32 Abstract ( 90 )   HTML ( 1 )   PDF (2499KB) ( 27 )   The growth of γ -In2Se3 thin films on mica by molecular beam epitaxy is studied. Single-crystalline γ -In2Se3 is achieved at a relatively low growth temperature. An ultrathin β -In2Se3 buffer layer is observed to nucleate and grow through a process of self-organization at initial deposition, which facilitates subsequent monolithic epitaxy of single-crystalline γ -In2Se3 at low temperature. Strong room-temperature photoluminescence and moderate optoelectronic response are observed in the achieved γ -In2Se3 thin films.
 The effects of Er 3 + ion concentration on 2.0-μ m emission performance in Ho 3 + /Tm 3 + co-doped Na 5Y 9F32 single crystal under 800-nm excitation Benli Ding(丁本利), Xiong Zhou(周雄), Jianli Zhang(章践立), Haiping Xia(夏海平), Hongwei Song(宋宏伟), and Baojiu Chen(陈宝玖) Chin. Phys. B, 2021, 30 (1):  017801.  DOI: 10.1088/1674-1056/abaede Abstract ( 77 )   HTML ( 1 )   PDF (1064KB) ( 25 )   Na5Y9F32 single crystals doped with ∼ 0.8-mol% Ho3 + , ∼ 1-mol% Tm3 + , and various Er3 + ion concentrations were prepared by a modified Bridgman method. The effects of Er3 + ion concentration on 2.0-μ m emission excited by an 800-nm laser diode were investigated with the help of their spectroscopic properties. The intensity of 2.0-μ m emission reached to maximum when the Er3 + ion concentration was ∼ 1 mol%. The energy transfer mechanisms between Er3 + , Ho3 + , and Tm3 + ions were identified from the change of the absorption spectra, the emission spectra, and the measured decay curves. The maximum 2.0-μ m emission cross section of the Er3 + /Ho3 + /Tm3 + tri-doped Na5Y9F32 single crystal reached 5.26 × 10 -21 cm2. The gain cross section spectra were calculated according to the absorption and emission cross section spectra. The cross section for ∼ 2.0-μ m emission became a positive gain once the inversion level of population was reached 30%. The energy transfer efficiency was further increased by 11.81% through the incorporation of Er3 + ion into Ho3 + /Tm3 + system estimated from the measured lifetimes of Ho3 + /Tm3 + -and Er3 + /Ho3 + /Tm3 + -doped Na5Y9F32 single crystals. The present results illustrated that the Er3 + /Ho3 + /Tm3 + tri-doped Na5Y9F32 single crystals can be used as promising candidate for 2.0-μ m laser.
 Effect of Sb composition on the band alignment of InAs/GaAsSb quantum dots Guangze Lu(陆光泽), Zunren Lv(吕尊仁), Zhongkai Zhang(张中恺), Xiaoguang Yang(杨晓光), and Tao Yang(杨涛) Chin. Phys. B, 2021, 30 (1):  017802.  DOI: 10.1088/1674-1056/abb309 Abstract ( 85 )   HTML ( 1 )   PDF (658KB) ( 34 )   Aiming to achieve InAs quantum dots (QDs) with a long carrier lifetime, the effects of Sb component in cap layers on the band alignment of the InAs/GaAsSb QDs have been studied. InAs QDs with high density and uniformity have been grown by molecular beam epitaxy. With increasing Sb composition, the InAs/GaAsSb QDs exhibit a significant red-shift and broadening photoluminescence (PL). With a high Sb component of 22%, the longest wavelength emission of the InAs/GaAs0.78Sb0.22 QDs occurs at 1.5 μ m at room temperature. The power-dependence PL measurements indicate that with a low Sb component of 14%, the InAs/GaAs0.86Sb0.14 QDs have a type-I and a type-II carrier recombination processes, respectively. With a high Sb component of 22%, the InAs/GaAs0.78Sb0.22 QDs have a pure type-II band alignment, with three type-II carrier recombination processes. Extracted from time-resolved PL decay traces, the carrier lifetime of the InAs/GaAs0.78Sb0.22 QDs reaches 16.86 ns, which is much longer than that of the InAs/GaAs0.86Sb0.14 QDs (2.07 ns). These results obtained here are meaningful to realize high conversion efficiency intermediate-band QD solar cells and other opto-electronic device.
 Optical properties of several ternary nanostructures Xiao-Long Tang(唐小龙), Xin-Lu Cheng(程新路), Hua-Liang Cao(曹华亮), and Hua-Dong Zeng(曾华东) Chin. Phys. B, 2021, 30 (1):  017803.  DOI: 10.1088/1674-1056/abaee6 Abstract ( 69 )   HTML ( 1 )   PDF (761KB) ( 32 )   To investigate the optical properties of the ternary nanostructures, the nanodisk, core-shell, and three-sphere structures are constructed. The extinction coefficients and electric near-field distributions of these structures are calculated by the discrete dipole approximation (DDA) method. The result shows that the nanodisk structure has the best extinction efficiency in the three structures. Furthermore, several three-material combinations of the nanodisk structures are investigated. The ternary nanodisk structure composed of TiO2 and two noble metals (Au, Ag or Pt) has higher extinction coefficient and near-field intensity than the nanodisk consisting of Au, TiO2 and a semiconductor (PbSe, Ge, MoS2, CdSe, CdS or TiO2). Especially, TiO2/Ag/Pt has the best extinction efficiency and the max electric near-field intensity. And the extinction spectra of TiO2/Ag/Pt and TiO2/Ag/Au structures are complementary in the visible range. This work conduces to the further research into ternary nanostructure and provides essential information about its performance in visible range.
 Quantum plasmons in the hybrid nanostructures of double vacancy defected graphene and metallic nanoarrays Rui Tang(唐睿), Yang Xu(徐阳), Hong Zhang(张红), and Xin-Lu Cheng(程新路) Chin. Phys. B, 2021, 30 (1):  017804.  DOI: 10.1088/1674-1056/abaedb Abstract ( 54 )   HTML ( 1 )   PDF (1336KB) ( 28 )   We study the plasmonic properties of hybrid nanostructures consisting of double vacancy defected graphene (DVDGr) and metallic nanoarrays using the time-dependent density functional theory. It is found that DVDGr with pure and mixed noble/transition-metal nanoarrays can produce a stronger light absorption due to the coherent resonance of plasmons than graphene nanostructures. Comparing with the mixed Au/Pd nanoarrays, pure Au nanoarrays have stronger plasmonic enhancement. Furthermore, harmonics from the hybrid nanostructures exposed to the combination of lasers ranged from ultraviolet to infrared and a controlling pulse are investigated theoretically. The harmonic plateau can be broadened significantly and the energy of harmonic spectra is dramatically extended by the controlling pulse. Thus, it is possible to tune the width and intensity of harmonic spectrum to achieve broadband absorption of radiation. The methodology described here not only improves the understanding of the surface plasmon effect used in a DVDGr-metal optoelectronic device but also may be applicable to different optical technologies.
 Analysis of secondary electron emission using the fractal method Chun-Jiang Bai(白春江), Tian-Cun Hu(胡天存), Yun He(何鋆), Guang-Hui Miao(苗光辉), Rui Wang(王瑞), Na Zhang(张娜), and Wan-Zhao Cui(崔万照) Chin. Phys. B, 2021, 30 (1):  017901.  DOI: 10.1088/1674-1056/abc2be Abstract ( 72 )   HTML ( 1 )   PDF (2312KB) ( 60 )   Based on the rough surface topography with fractal parameters and the Monte-Carlo simulation method for secondary electron emission properties, we analyze the secondary electron yield (SEY) of a metal with rough surface topography. The results show that when the characteristic length scale of the surface, G, is larger than 1× 10-7, the surface roughness increases with the increasing fractal dimension D. When the surface roughness becomes larger, it is difficult for entered electrons to escape surface. As a result, more electrons are collected and then SEY decreases. When G is less than 1× 10-7, the effect of the surface topography can be ignored, and the SEY almost has no change as the dimension D increases. Then, the multipactor thresholds of a C-band rectangular impedance transfer and an ultrahigh-frequency-band coaxial impedance transfer are predicted by the relationship between the SEY and the fractal parameters. It is verified that for practical microwave devices, the larger the parameter G is, the higher the multipactor threshold is. Also, the larger the value of D, the higher the multipactor threshold.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
 Enhanced mobility of MoS2 field-effect transistors by combining defect passivation with dielectric-screening effect Zhao Li(李钊), Jing-Ping Xu(徐静平), Lu Liu(刘璐), and Xin-Yuan Zhao(赵心愿) Chin. Phys. B, 2021, 30 (1):  018102.  DOI: 10.1088/1674-1056/abb30f Abstract ( 172 )   HTML ( 2 )   PDF (878KB) ( 53 )   A facile method of combining the defect engineering with the dielectric-screening effect is proposed to improve the electrical performance of MoS2 transistors. It is found that the carrier mobility of the transistor after the sulfur treatment on the MoS2 channel is greatly enhanced due to the reduction of the sulfur vacancies during vulcanization of MoS2. Furthermore, as compared to those transistors with HfO2 and SiO2 as the gate dielectric, the Al2O3-gate dielectric MoS2 FET shows a better electrical performance after the sulfur treatment, with a lowered subthreshold swing of 179.4 mV/dec, an increased on/off ratio of 2.11 × 106, and an enhanced carrier mobility of 64.74 cm2/Vs (about twice increase relative to the non-treated MoS2 transistor with SiO2 as the gate dielectric). These are mainly attributed to the fact that a suitable k-value gate dielectric can produce a dominant dielectric-screening effect overwhelming the phonon scattering, increasing the carrier mobility, while a larger k-value gate dielectric will enhance the phonon scattering to counteract the dielectric-screening effect, reducing the carrier mobility.
 A MOVPE method for improving InGaN growth quality by pre-introducing TMIn Zi-Kun Cao(曹子坤), De-Gang Zhao(赵德刚), Jing Yang(杨静), Jian-Jun Zhu(朱建军), Feng Liang(梁锋), and Zong-Shun Liu(刘宗顺) Chin. Phys. B, 2021, 30 (1):  018103.  DOI: 10.1088/1674-1056/abb801 Abstract ( 95 )   HTML ( 1 )   PDF (911KB) ( 56 )   We propose a metal organic vapor phase epitaxy (MOVPE) method of pre-introducing TMIn during the growth of u-GaN to improve the subsequent growth of InGaN and discuss the impact of this method in detail. Monitoring the MOVPE by the interference curve generated by the laser incident on the film surface, we found that this method avoided the problem of the excessive InGaN growth rate. Further x-ray diffraction (XRD), photoluminescence (PL), and atomic force microscope (AFM) tests showed that the quality of InGaN is improved. It is inferred that by introducing TMIn in advance, the indium atom can replace the gallium atom in the reactor walls, delivery pipes, and other corners. Hence the auto-incorporation of gallium can be reduced when InGaN is grown, so as to improve the material quality.
 Numerical research on effect of overlap ratio on thermal-stress behaviors of the high-speed laser cladding coating Xiaoxi Qiao(乔小溪), Tongling Xia(夏同领), and Ping Chen(陈平) Chin. Phys. B, 2021, 30 (1):  018104.  DOI: 10.1088/1674-1056/abcf9b Abstract ( 47 )   HTML ( 2 )   PDF (4231KB) ( 53 )   High-speed laser cladding technology, a kind of surface technology to improve the wear-resistance and corrosion-resistance of mechanical parts, has the characterizations of fast scan speed, high powder utilization rate, and high cladding efficiency. However, its thermal-stress evolution process is very complex, which has a great influence on the residual stress and deformation. In the paper, the numerical models for the high-speed laser cladding coatings with overlap ratios of 10%, 30%, and 50% are developed to investigate the influence rules of overlap ratio on the thermal-stress evolution, as well as the residual stresses and deformations. Results show that the heat accumulation can reheat and preheat the adjacent track coating and substrate, resulting in stress release of the previous track coating and decreased longitudinal stress peak of the next track coating. With the overlap ratio increasing, the heat accumulation and the corresponding maximum residual stress position tend to locate in the center of the cladding coating, where the coating has a high crack susceptibility. For a small overlap ratio of 10%, there are abrupt stress changes from tensile stress to compressive stress at the lap joint, due to insufficient input energy in the position. Increasing the overlap ratio can alleviate the abrupt stress change and reduce the residual deformation but increase the average residual stress and enlarge the hardening depth. This study reveals the mechanism of thermal-stress evolution, and provides a theoretical basis for improving the coating quality.
 Continuous-wave operation of InAs/InP quantum dot tunable external-cavity laser grown by metal-organic chemical vapor deposition Yan Wang(王岩), Shuai Luo(罗帅), Haiming Ji(季海铭), Di Qu(曲迪), and Yidong Huang(黄翊东) Chin. Phys. B, 2021, 30 (1):  018106.  DOI: 10.1088/1674-1056/abcfa4 Abstract ( 74 )   HTML ( 1 )   PDF (2142KB) ( 22 )   We demonstrate high-performance broadband tunable external-cavity lasers (ECLs) with the metal-organic chemical vapor deposition (MOCVD) grown InAs/InP quantum dots (QDs) structures. Without cavity facet coatings, the 3-dB spectral bandwidth of the Fabry-Perot (FP) laser is approximately 10.8 nm, while the tuning bandwidth of ECLs is 45 nm. Combined with the anti-reflection (AR) /high-reflection (HR) facet coating, a 92 nm bandwidth tuning range has been obtained with the wavelength covering from 1414 nm to 1506 nm. In most of the tuning range, the threshold current density is lower than 1.5 kA/cm2. The maximum output power of 6.5 mW was achieved under a 500 mA injection current. All achievements mentioned above were obtained under continuous-wave (CW) mode at room temperature (RT).
 Multi-phase-field simulation of austenite peritectic solidification based on a ferrite grain Chao Yang(杨超), Jing Wang(王静), Junsheng Wang(王俊升), Yu Liu(刘瑜), Guomin Han(韩国民), Haifeng Song(宋海峰), and Houbing Huang(黄厚兵) Chin. Phys. B, 2021, 30 (1):  018201.  DOI: 10.1088/1674-1056/abc54b Abstract ( 88 )   HTML ( 1 )   PDF (971KB) ( 62 )   A multi-phase-field model is implemented to investigate the peritectic solidification of Fe-C alloy. The nucleation mode of austenite is based on the local driving force, and two different thicknesses of the primary austenite on the surface of the ferrite equiaxed crystal grain are used as the initial conditions. The simulation shows the multiple interactions of ferrite, austenite, and liquid phases, and the effects of carbon diffusion, which presents the non-equilibrium dynamic process during Fe-C peritectic solidification at the mesoscopic scale. This work not only reveals the influence of the austenite nucleation position, but also clarifies the formation mechanism of liquid phase channels and molten pools. Therefore, the present study contributes to the understanding of the micro-morphology and micro-segregation evolution mechanisms of Fe-C alloy during peritectic solidification.
 Stretchable electromagnetic interference shielding and antenna for wireless strain sensing by anisotropic micron-steel-wire based conductive elastomers Xiaoyu Hu(胡晓宇), Linlin Mou(牟琳琳), and Zunfeng Liu(刘遵峰) Chin. Phys. B, 2021, 30 (1):  018401.  DOI: 10.1088/1674-1056/abc2b3 Abstract ( 70 )   HTML ( 1 )   PDF (1343KB) ( 48 )   We prepare stretchable elastic electromagnetic interference (EMI) shielding and stretchable antenna for wireless strain sensing using an elastic composite comprising commercial steel wool as a conducting element. The prepared elastic conductor shows anisotropic electrical properties in response to the external force. In the stretchable range, the electrical resistance abnormally decreases with the increase of tensile deformation. The EMI shielding effectiveness of the elastic conductor can reach above -30 dB under 80% tensile strain. The resonance frequency of the dipole antenna prepared by the elastic conductor is linearly correlated with the tensile strain, which can be used as a wireless strain sensor. The transmission efficiency is stable at about -15 dB when stretched to 50% strain, with attenuation less than 5%. The current research provides an effective solution for stretchable EMI shielding and wireless strain sensing integrated with signal transmission by an antenna.
 Influences of increasing gate stem height on DC and RF performances of InAlAs/InGaAs InP-based HEMTs Zhi-Hang Tong(童志航), Peng Ding(丁芃), Yong-Bo Su(苏永波), Da-Hai Wang(王大海), and Zhi Jin(金智) Chin. Phys. B, 2021, 30 (1):  018501.  DOI: 10.1088/1674-1056/abb30d Abstract ( 109 )   HTML ( 2 )   PDF (2201KB) ( 30 )   The T-gate stem height of InAlAs/InGaAs InP-based high electron mobility transistor (HEMT) is increased from 165 nm to 250 nm. The influences of increasing the gate stem height on the direct current (DC) and radio frequency (RF) performances of device are investigated. A 120-nm-long gate, 250-nm-high gate stem device exhibits a higher threshold voltage (V th) of 60 mV than a 120-nm-long gate devices with a short gate stem, caused by more Pt distributions on the gate foot edges of the high Ti/Pt/Au gate. The Pt distribution in Schottky contact metal is found to increase with the gate stem height or the gate length increasing, and thus enhancing the Schottky barrier height and expanding the gate length，which can be due to the increased internal tensile stress of Pt. The more Pt distributions for the high gate stem device also lead to more obvious Pt sinking, which reduces the distance between the gate and the InGaAs channel so that the transconductance (g m) of the high gate stem device is 70 mS/mm larger than that of the short stem device. As for the RF performances, the gate extrinsic parasitic capacitance decreases and the intrinsic transconductance increases after the gate stem height has been increased, so the RF performances of device are obviously improved. The high gate stem device yields a maximum f t of 270 GHz and f max of 460 GHz, while the short gate stem device has a maximum f t of 240 GHz and the f max of 370 GHz.
 Novel CMOS image sensor pixel to improve charge transfer speed and efficiency by overlapping gate and temporary storage diffusing node Cui Yang(杨翠), Guo-Liang Peng(彭国良), Wei Mao(毛维), Xue-Feng Zheng(郑雪峰), Chong Wang(王冲), Jin-Cheng Zhang(张进成), and Yue Hao(郝跃) Chin. Phys. B, 2021, 30 (1):  018502.  DOI: 10.1088/1674-1056/abc53f Abstract ( 103 )   HTML ( 1 )   PDF (1320KB) ( 75 )   A novel CMOS image sensor (CIS) pinned photodiode (PPD) pixel, named as O-T pixel, is proposed and investigated by TCAD simulations. Compared with the conventional PPD pixel, the proposed pixel features the overlapping gate (OG) and the temporary storage diffusing (TSD) region, based on which the several-nanosecond-level charge transfer could be achieved and the complete charge transfer from the PPD to the floating node (FD) could be realized. And systematic analyses of the influence of the doping conditions of the proposed processes, the OG length, and the photodiode length on the transfer performances of the proposed pixel are conducted. Optimized simulation results show that the total charge transfer time could reach about 5.862 ns from the photodiode to the sensed node and the corresponding charge transfer efficiency could reach as high as 99.995% in the proposed pixel with 10 μm long photodiode and 2.22 μm long OG. These results demonstrate a great potential of the proposed pixel in high-speed applications.
 Retrieval of multiple scattering contrast from x-ray analyzer-based imaging Heng Chen(陈恒), Bo Liu(刘波), Li-Ming Zhao(赵立明), Kun Ren(任坤), and Zhi-Li Wang(王志立) Chin. Phys. B, 2021, 30 (1):  018701.  DOI: 10.1088/1674-1056/abbbed Abstract ( 60 )   HTML ( 1 )   PDF (623KB) ( 26 )   We present a moment-based alternative approach to retrieve multiple scattering contrasts from x-ray analyzer-based imaging. By use of the properties of moments of convolutions, the multiple-image radiography approach is theoretically validated. Furthermore, higher order moments of the object scattering distribution, inaccessible in multiple-image radiography, are simultaneously provided by this alternative approach. It is experimentally demonstrated that the skew and kurtosis information related to the distribution of sub-pixel features within the object can be obtained from those complementary contrasts. Finally, the sensitivity of the retrieved multiple scattering contrasts is investigated experimentally. The finding that the sensitivity is inversely proportional to the square root of the detected photon number essentially indicates that the retrieval of moments with an order higher than two can be achieved without increasing exposure time or dose. The presented alternative approach provides an access to the exploitation of multiple scattering contrasts, which is expected to be useful in biomedical research, materials science, security screening, etc.
 Effect of interaction between loop bases and ions on stability of G-quadruplex DNA Han-Zhen Qiao(乔汉真), Yuan-Yan Wu(吴园燕), Yusong Tu(涂育松), and Cong-Min Ji(祭聪敏) Chin. Phys. B, 2021, 30 (1):  018702.  DOI: 10.1088/1674-1056/abb7f7 Abstract ( 75 )   HTML ( 1 )   PDF (4147KB) ( 24 )   G-quadruplexes (GQs) are guanine-rich, non-canonical nucleic acid structures that play fundamental roles in biological processes. The topology of GQs is associated with the sequences and lengths of DNA, the types of linking loops, and the associated metal cations. However, our understanding on the basic physical properties of the formation process and the stability of GQs is rather limited. In this work, we employed ab initio, molecular dynamics (MD), and steered MD (SMD) simulations to study the interaction between loop bases and ions, and the effect on the stability of G-quadruplex DNA, the Drude oscillator model was used in MD and SMD simulations as a computationally efficient manner method for modeling electronic polarization in DNA ion solutions. We observed that the binding energy between DNA bases and ions (K + /Na + ) is about the base stacking free energies indicates that there will be a competition among the binding of M + -base, H-bonds between bases, and the base-stacking while ions were bound in loop of GQs. Our SMD simulations indicated that the side loop inclined to form the base stacking while the loop sequence was Thy or Ade, and the cross-link loop upon the G-tetrads was not easy to form the base stacking. The base stacking side loop complex K + was found to have a good stabilization synergy. Although a stronger interaction was observed to exist between Cyt and K + , such an interaction was unable to promote the stability of the loop with the sequence Cyt.
 Network analysis and spatial agglomeration of China's high-speed rail: A dual network approach Wei Wang(王微), Wen-Bo Du(杜文博), Wei-Han Li(李威翰), Lu (Carol) Tong(佟路), and Jiao-E Wang(王姣娥) Chin. Phys. B, 2021, 30 (1):  018901.  DOI: 10.1088/1674-1056/abaee3 Abstract ( 133 )   HTML ( 2 )   PDF (1498KB) ( 75 )   China has the largest high-speed railway (HSR) system in the world, and it has gradually reshaped the urban network. The HSR system can be represented as different types of networks in terms of the nodes and various relationships (i.e., linkages) between them. In this paper, we first introduce a general dual network model, including a physical network (PN) and a logical network (LN) to provide a comparative analysis for China's high-speed rail network via complex network theory. The PN represents a layout of stations and rail tracks, and forms the basis for operating all trains. The LN is a network composed of the origin and destination stations of each high-speed train and the train flows between them. China's high-speed railway (CHSR) has different topological structures and link strengths for PN in comparison with the LN. In the study, the community detection is used to analyze China's high-speed rail networks and several communities are found to be similar to the layout of planned urban agglomerations in China. Furthermore, the hierarchies of urban agglomerations are different from each other according to the strength of inter-regional interaction and intra-regional interaction, which are respectively related to location and spatial development strategies. Moreover, a case study of the Yangtze River Delta shows that the hub stations have different resource divisions and are major contributors to the gap between train departure and arrival flows.
 A new heuristics model of simulating pedestrian dynamics based on Voronoi diagram Xin-Sen Wu(武鑫森), Hao Yue(岳昊), Qiu-Mei Liu(刘秋梅), Xu Zhang(张旭), and Chun-Fu Shao(邵春福) Chin. Phys. B, 2021, 30 (1):  018902.  DOI: 10.1088/1674-1056/abb3f5 Abstract ( 81 )   HTML ( 2 )   PDF (4016KB) ( 37 )   A new heuristics model based on the Voronoi diagram is presented to simulate pedestrian dynamics with the non-crowded state, in which these mechanisms of preference demand evading and surpassing, microscopic anti-deadlock, and site-fine-tuning are considered. The preference demand describes the willingness determination of detouring or following other pedestrians. In the evading and surpassing mechanisms, in order to achieve a balance between avoiding conflicts and minimizing detour distances, a new pair of concepts: "allow-areas and denial-areas" are introduced to divide the feasible region for pedestrians detour behaviors, in which the direction and magnitude of detour velocity are determined. A microscopic anti-deadlock mechanism is inserted to avoid deadlock problem of the counter-directional pedestrian. A site-fine-tuning mechanism is introduced to describe the behavior of avoiding getting too close to the neighbors in pedestrian movement. The presented model is verified through multiple scenarios, including the uni-or bi-direction pedestrian flow in the corridor without obstacles, the uni-direction pedestrian flow in the corridor with obstacles, and the pedestrian evacuation from a room with single-exit. The simulation results show that the velocity-density relationship is consistent with empirical data. Some self-organizing phenomena, such as lanes formation and arching are observed in the simulation. When pedestrians detour an obstacle, the avoiding area before the obstacle and the unoccupied area after the obstacle can be observed. When pedestrians evacuate through a bottleneck without panic, the fan-shaped crowd can be found, which is consistent with the actual observation. It is also found that the behavior of following others in an orderly manner is more conducive to the improvement of the overall movement efficiency when the crowd moves in a limited space.
ERRATUM
 Erratum to "Fabrication of Tl2Ba2CaCu2O8 superconducting films without thallium pellets" Teng-Da Xu(徐腾达), Jian Xing(邢建), Li-Tian Wang(王荔田), Jin-Li Zhang(张金利), Sheng-Hui Zhao(赵生辉), Yang Xiong(熊阳), Xin-Jie Zhao(赵新杰), Lu Ji(季鲁), Xu Zhang(张旭), and Ming He(何明) Chin. Phys. B, 2021, 30 (1):  019901.  DOI: 10.1088/1674-1056/abd46c Abstract ( 129 )   HTML ( 3 )   PDF (598KB) ( 17 )   Figure 2 in the original paper (Chin. Phys. B 27057403 (2018)]) is replaced by a new one.
ISSN 1674-1056   CN 11-5639/O4
, Vol. 30, No. 1