Chin. Phys. B

Topological photonic states in gyromagnetic photonic crystals: Physics, properties, and applications

Jianfeng Chen(陈剑锋) and Zhi-Yuan Li(李志远)

Chin. Phys. B, 2022, 31 (11): 114207. DOI: 10.1088/1674-1056/ac92d7

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Topological photonic states (TPSs) as a new type of waveguide state with one-way transport property can resist backscattering and are impervious to defects, disorders and metallic obstacles. Gyromagnetic photonic crystal (GPC) is the first artificial microstructure to implement TPSs, and it is also one of the most important platforms for generating truly one-way TPSs and exploring their novel physical properties, transport phenomena, and advanced applications. Herein, we present a brief review of the fundamental physics, novel properties, and practical applications of TPSs based on GPCs. We first examine chiral one-way edge states existing in uniformly magnetized GPCs of ordered and disordered lattices, antichiral one-way edge states in cross magnetized GPCs, and robust one-way bulk states in heterogeneously magnetized GPCs. Then, we discuss the strongly coupling effect between two co-propagating (or counter-propagating) TPSs and the resulting physical phenomena and device applications. Finally, we analyze the key issues and prospect the future development trends for TPSs in GPCs. The purpose of this brief review is to provide an overview of the main features of TPSs in GPC systems and offer a useful guidance and motivation for interested scientists and engineers working in related scientific and technological areas.

From microelectronics to spintronics and magnonics

Xiu-Feng Han(韩秀峰), Cai-Hua Wan(万蔡华), Hao Wu(吴昊), Chen-Yang Guo(郭晨阳), Ping Tang(唐萍), Zheng-Ren Yan(严政人), Yao-Wen Xing(邢耀文), Wen-Qing He(何文卿), and Guo-Qiang Yu(于国强)

Chin. Phys. B, 2022, 31 (11): 117504. DOI: 10.1088/1674-1056/ac9048

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In this review, the recent developments in microelectronics, spintronics, and magnonics have been summarized and compared. Firstly, the history of the spintronics has been briefly reviewed. Moreover, the recent development of magnonics such as magnon-mediated current drag effect (MCDE), magnon valve effect (MVE), magnon junction effect (MJE), magnon blocking effect (MBE), magnon-mediated nonlocal spin Hall magnetoresistance (MNSMR), magnon-transfer torque (MTT) effect, and magnon resonant tunneling (MRT) effect, magnon skin effect (MSE), etc., existing in magnon junctions or magnon heterojunctions, have been summarized and their potential applications in memory and logic devices, etc., are prospected, from which we can see a promising future for spintronics and magnonics beyond micro-electronics.

Epitaxy of III-nitrides on two-dimensional materials and its applications

Yu Xu(徐俞), Jianfeng Wang(王建峰), Bing Cao(曹冰), and Ke Xu(徐科)

Chin. Phys. B, 2022, 31 (11): 117702. DOI: 10.1088/1674-1056/ac921f

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III-nitride semiconductor materials have excellent optoelectronic properties, mechanical properties, and chemical stability, which have important applications in the field of optoelectronics and microelectronics. Two-dimensional (2D) materials have been widely focused in recent years due to their peculiar properties. With the property of weak bonding between layers of 2D materials, the growth of III-nitrides on 2D materials has been proposed to solve the mismatch problem caused by heterogeneous epitaxy and to develop substrate stripping techniques to obtain high-quality, low-cost nitride materials for high-quality nitride devices and their extension in the field of flexible devices. In this progress report, the main methods for the preparation of 2D materials, and the recent progress and applications of different techniques for the growth of III-nitrides based on 2D materials are reviewed.

Understanding the battery safety improvement enabled by a quasi-solid-state battery design

Luyu Gan(甘露雨), Rusong Chen(陈汝颂), Xiqian Yu(禹习谦), and Hong Li(李泓)

Chin. Phys. B, 2022, 31 (11): 118202. DOI: 10.1088/1674-1056/ac9221

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The rapid development of lithium-ion batteries (LIBs) is faced with challenge of its safety bottleneck, calling for design and chemistry innovations. Among the proposed strategies, the development of solid-state batteries (SSBs) seems the most promising solution, but to date no practical SSB has been in large-scale application. Practical safety performance of SSBs is also challenged. In this article, a brief review on LIB safety issue is made and the safety short boards of LIBs are emphasized. A systematic safety design in quasi-SSB chemistry is proposed to conquer the intrinsic safety weak points of LIBs and the effects are accessed based on existing studies. It is believed that a systematic and targeted solution in SSB chemistry design can effectively improve the battery safety, promoting larger-scale application of LIBs.

Could two-dimensional perovskites fundamentally solve the instability of perovskite photovoltaics

Luoran Chen(陈烙然), Hu Wang(王虎), and Yuchuan Shao(邵宇川)

Chin. Phys. B, 2022, 31 (11): 117803. DOI: 10.1088/1674-1056/ac693e

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The high efficiency and low production cost enable the halide perovskite solar cells as a promising technology for the next generation photovoltaics. Nevertheless, the relatively poor stability of the organic-inorganic halide perovskites hinders their commercial applications. In the past few years, two-dimensional (2D) perovskite has emerged as a more stable alternative to the three-dimensional (3D) counterparts and attracted intense research interests. Although many attempts and advances have been made, it is still ambiguous that whether the 2D perovskites could bring closure to the stability issue. To answer this essential question, a systematic study of the nature of 2D halide perovskites is necessary. Here, we focus on the stability investigations of 2D perovskites from different perspectives, especially light, heat, ion migration and strain. Several remaining challenges and opening problems are also discussed. With further material and device engineering, we believe that the 2D perovskites would promote perovskite solar cells to a promising future.

A silazane additive for CsPbI₂Br perovskite solar cells

Ruiqi Cao(曹瑞琪), Yaochang Yue(乐耀昌), Hong Zhang(张弘), Qian Cheng(程倩), Boxin Wang(王博欣), Shilin Li(李世麟), Yuan Zhang(张渊), Shuhong Li(李书宏), and Huiqiong Zhou(周惠琼)

Chin. Phys. B, 2022, 31 (11): 110101. DOI: 10.1088/1674-1056/ac7c01

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Adding additives into peroskite precursor solution has been proven as a simple and efficient strategy to improve the quality of peroskite films. In this work, we demonstrate an effective additive strategy to improve the quality of all-inorganic perovskite films by adding a novel silazane additive heptamethyldisilazane (HDMS). The power conversion efficiency (PCE) of the optimized devices is enhanced from 14.55% to 15.31% with an open-circuit voltage over 1.26 V due to the higher quality perovskite films with lower trap density after the incorporation of HDMS. More interestingly, the HDMS devices exhibit superior humidity and thermal stability compared with the control ones. This work provides a simple and efficient strategy to enhance the device performance and stability of all-inorganic perovskite solar cells, which could facilitate its commercialization.

Defect physics of the quasi-two-dimensional photovoltaic semiconductor GeSe

Saichao Yan(闫赛超), Jinchen Wei(魏金宸), Shanshan Wang(王珊珊), Menglin Huang(黄梦麟), Yu-Ning Wu(吴宇宁), and Shiyou Chen(陈时友)

Chin. Phys. B, 2022, 31 (11): 116103. DOI: 10.1088/1674-1056/ac685f

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GeSe has recently emerged as a photovoltaic absorber material due to its attractive optical and electrical properties as well as earth abundancy and low toxicity. However, the efficiency of GeSe thin-film solar cells (TFSCs) is still low compared to the Shockley-Queisser limit. Point defects are believed to play important roles in the electrical and optical properties of GeSe thin films. Here, we perform first-principles calculations to study the defect characteristics of GeSe. Our results demonstrate that no matter under the Ge-rich or Se-rich condition, the Fermi level is always located near the valence band edge, leading to the p-type conductivity of undoped samples. Under Se-rich condition, the Ge vacancy (V_Ge) has the lowest formation energy, with a (0/2-) charge-state transition level at 0.22 eV above the valence band edge. The high density (above 10¹⁷ cm^-3) and shallow level of V_Ge imply that it is the p-type origin of GeSe. Under Se-rich growth condition, Se_i has a low formation energy in the neutral state, but it does not introduce any defect level in the band gap, suggesting that it neither contributes to electrical conductivity nor induces non-radiative recombination. In addition, Ge_i introduces a deep charge-state transition level, making it a possible recombination center. Therefore, we propose that the Se-rich condition should be adopted to fabricate high-efficiency GeSe solar cells.

Sputtered SnO₂ as an interlayer for efficient semitransparent perovskite solar cells

Zheng Fang(方正), Liu Yang(杨柳), Yongbin Jin(靳永斌), Kaikai Liu(刘凯凯), Huiping Feng(酆辉平), Bingru Deng(邓冰如), Lingfang Zheng(郑玲芳), Changcai Cui(崔长彩), Chengbo Tian(田成波), Liqiang Xie(谢立强), Xipeng Xu(徐西鹏), and Zhanhua Wei(魏展画)

Chin. Phys. B, 2022, 31 (11): 118801. DOI: 10.1088/1674-1056/ac67c5

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SnO₂ is widely used as the electron transport layer (ETL) in perovskite solar cells (PSCs) due to its excellent electron mobility, low processing temperature, and low cost. And the most common way of preparing the SnO₂ ETL is spin-coating using the corresponding colloid solution. However, the spin-coated SnO₂ layer is sometimes not so compact and contains pinholes, weakening the hole blocking capability. Here, a SnO₂ thin film prepared through magnetron-sputtering was inserted between ITO and the spin-coated SnO₂ acted as an interlayer. This strategy can combine the advantages of efficient electron extraction and hole blocking due to the high compactness of the sputtered film and the excellent electronic property of the spin-coated SnO₂. Therefore, the recombination of photo-generated carriers at the interface is significantly reduced. As a result, the semitransparent perovskite solar cells (with a bandgap of 1.73 eV) based on this double-layered SnO₂ demonstrate a maximum efficiency of 17.7% (stabilized at 17.04%) with negligible hysteresis. Moreover, the shelf stability of the device is also significantly improved, maintaining 95% of the initial efficiency after 800-hours of aging.

TiO₂/SnO₂ electron transport double layers with ultrathin SnO₂ for efficient planar perovskite solar cells

Can Li(李灿), Hongyu Xu(徐宏宇), Chongyang Zhi(郅冲阳), Zhi Wan(万志), and Zhen Li(李祯)

Chin. Phys. B, 2022, 31 (11): 118802. DOI: 10.1088/1674-1056/ac8349

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The electron transport layer (ETL) plays an important role on the performance and stability of perovskite solar cells (PSCs). Developing double ETL is a promising strategy to take the advantages of different ETL materials and avoid their drawbacks. Here, an ultrathin SnO₂ layer of ～ 5 nm deposited by atomic layer deposit (ALD) was used to construct a TiO₂/SnO₂ double ETL, improving the power conversion efficiency (PCE) from 18.02% to 21.13%. The ultrathin SnO₂ layer enhances the electrical conductivity of the double layer ETLs and improves band alignment at the ETL/perovskite interface, promoting charge extraction and transfer. The ultrathin SnO₂ layer also passivates the ETL/perovskite interface, suppressing nonradiative recombination. The double ETL achieves outstanding stability compared with PSCs with TiO₂ only ETL. The PSCs with double ETL retains 85% of its initial PCE after 900 hours illumination. Our work demonstrates the prospects of using ultrathin metal oxide to construct double ETL for high-performance PSCs.

Electron delocalization enhances the thermoelectric performance of misfit layer compound (Sn_1-xBi_xS)_1.2(TiS₂)₂

Xin Zhao(赵昕), Xuanwei Zhao(赵轩为), Liwei Lin(林黎蔚), Ding Ren(任丁), Bo Liu(刘波), and Ran Ang(昂然)

Chin. Phys. B, 2022, 31 (11): 117202. DOI: 10.1088/1674-1056/ac6493

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The misfit layer compound (SnS)_1.2(TiS₂)₂ is a promising low-cost thermoelectric material because of its low thermal conductivity derived from the superlattice-like structure. However, the strong covalent bonds within each constituent layer highly localize the electrons thereby it is highly challenging to optimize the power factor by doping or alloying. Here, we show that Bi doping at the Sn site markedly breaks the covalent bonds networks and highly delocalizes the electrons. This results in a high charge carrier concentration and enhanced power factor throughout the whole temperature range. It is highly remarkable that Bi doping also significantly reduces the thermal conductivity by suppressing the heat conduction carried by phonons, indicating that it independently modulates phonon and charge transport properties. These effects collectively give rise to a maximum ZT of 0.3 at 720 K. In addition, we apply the single Kane band model and the Debye-Callaway model to clarify the electron and phonon transport mechanisms in the misfit layer compound (SnS)_1.2(TiS₂)₂.

Laser-modified luminescence for optical data storage

Xin Wei(魏鑫), Weiwei Zhao(赵伟玮), Ting Zheng(郑婷), Junpeng Lü(吕俊鹏), Xueyong Yuan(袁学勇), and Zhenhua Ni(倪振华)

Chin. Phys. B, 2022, 31 (11): 117901. DOI: 10.1088/1674-1056/ac9824

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The yearly growing quantities of dataflow create a desired requirement for advanced data storage methods. Luminescent materials, which possess adjustable parameters such as intensity, emission center, lifetime, polarization, etc., can be used to enable multi-dimensional optical data storage (ODS) with higher capacity, longer lifetime and lower energy consumption. Multiplexed storage based on luminescent materials can be easily manipulated by lasers, and has been considered as a feasible option to break through the limits of ODS density. Substantial progresses in laser-modified luminescence based ODS have been made during the past decade. In this review, we recapitulated recent advancements in laser-modified luminescence based ODS, focusing on the defect-related regulation, nucleation, dissociation, photoreduction, ablation, etc. We conclude by discussing the current challenges in laser-modified luminescence based ODS and proposing the perspectives for future development.

Photoreflectance system based on vacuum ultraviolet laser at 177.3 nm

Wei-Xia Luo(罗伟霞), Xue-Lu Liu(刘雪璐), Xiang-Dong Luo(罗向东), Feng Yang(杨峰), Shen-Jin Zhang(张申金), Qin-Jun Peng(彭钦军), Zu-Yan Xu(许祖彦), and Ping-Heng Tan(谭平恒)

Chin. Phys. B, 2022, 31 (11): 110701. DOI: 10.1088/1674-1056/ac89e4

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Photoreflectance (PR) spectroscopy is a powerful and non-destructive experimental technique to explore interband transitions of semiconductors. In most PR systems, the photon energy of the pumping beam is usually chosen to be higher than the bandgap energy of the sample. To the best of our knowledge, the highest energy of pumping laser in reported PR systems is 5.08 eV (244 nm), not yet in the vacuum ultraviolet (VUV) region. In this work, we report the design and construction of a PR system pumped by VUV laser of 7.0 eV (177.3 nm). At the same time, dual-modulated technique is applied and a dual channel lock-in-amplifier is integrated into the system for efficient PR measurement. The system's performance is verified by the PR spectroscopy measurement of well-studied semiconductors, which testifies its ability to probe critical-point energies of the electronic band in semiconductors from ultraviolet to near-infrared spectral region.

Amplitude modulation excitation for cancellous bone evaluation using a portable ultrasonic backscatter instrumentation

Boyi Li(李博艺), Chengcheng Liu(刘成成), Xin Liu(刘欣), Tho N. H. T. Tran, Ying Li(李颖), Dan Li(李旦), Dongsheng Bi(毕东生), Duwei Liu(刘度为), and Dean Ta(他得安)

Chin. Phys. B, 2022, 31 (11): 114303. DOI: 10.1088/1674-1056/ac7a18

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The ultrasonic backscatter (UB) has the advantage of non-invasively obtaining bone density and structure, expected to be an assessment tool for early diagnosis osteoporosis. All former UB measurements were based on exciting a short single-pulse and analyzing the ultrasonic signals backscattered in bone. This study aims to examine amplitude modulation (AM) ultrasonic excitation with UB measurements for predicting bone characteristics. The AM multiple lengths excitation and backscatter measurement (AM-UB) functions were integrated into a portable ultrasonic instrument for bone characterization. The apparent integrated backscatter coefficient in the AM excitation (AIB_AM) was evaluated on the AM-UB instrumentation. The correlation coefficients of the AIB_AM estimating volume fraction (BV/TV), structure model index (SMI), and bone mineral density (BMD) were then analyzed. Significant correlations (|R| = 0.82-0.93, p < 0.05) were observed between the AIB_AM, BV/TV, SMI, and BMD. By growing the AM excitation length, the AIB_AM values exhibit more stability both in 1.0-MHz and 3.5-MHz measurements. The recommendations in AM-UB measurement were that the avoided length (T1) should be lower than AM excitation length, and the analysis length (T2) should be enough long but not more than AM excitation length. The authors conducted an AM-UB measurement for cancellous bone characterization. Increasing the AM excitation length could substantially enhance AIB_AM values stability with varying analyzed signals. The study suggests the portable AM-UB instrument with the integration of real-time analytics software that might provide a potential tool for osteoporosis early screening.

A design of resonant cavity with an improved coupling-adjusting mechanism for the W-band EPR spectrometer

Yu He(贺羽), Runqi Kang(康润琪), Zhifu Shi(石致富), Xing Rong(荣星), and Jiangfeng Du(杜江峰)

Chin. Phys. B, 2022, 31 (11): 117601. DOI: 10.1088/1674-1056/ac7bfd

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We report a new design of resonant cavity for a W-band electron paramagnetic resonance (EPR) spectrometer. An improved coupling-adjusting mechanism, which is robust, compact, and suits with both solenoid-type and split-pair magnets, is utilized on the cavity, and thus enables both continuous-wave (CW) and pulsed EPR experiments. It is achieved by a tiny metal cylinder in the iris. The coupling coefficient can be varied from 0.2 to 17.9. Furthermore, two pistons at each end of the cavity allow for adjustment of the resonant frequency. A horizontal TE₀₁₁ geometry also makes the cavity compatible with the two frequently used types of magnets. The coupling-varying ability has been demonstrated by reflection coefficient (S₁₁) measurement. CW and pulsed EPR experiments have been conducted. The performance data indicates a prospect of wide applications of the cavity in fields of physics, chemistry and biology.

Structure of continuous matrix product operator for transverse field Ising model: An analytic and numerical study ^Hot!

Yueshui Zhang(张越水) and Lei Wang(王磊)

Chin. Phys. B, 2022, 31 (11): 110205. DOI: 10.1088/1674-1056/ac8a8f

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We study the structure of the continuous matrix product operator (cMPO)^[1] for the transverse field Ising model (TFIM). We prove TFIM's cMPO is solvable and has the form $T=\rm{e}^{-\frac{1}{2}\hat{H}_{\rm F}}$. $\hat{H}_{\rm F}$ is a non-local free fermionic Hamiltonian on a ring with circumference $\beta$, whose ground state is gapped and non-degenerate even at the critical point. The full spectrum of $\hat{H}_{\rm F}$ is determined analytically. At the critical point, our results verify the state-operator-correspondence^[2] in the conformal field theory (CFT). We also design a numerical algorithm based on Bloch state ansatz to calculate the low-lying excited states of general (Hermitian) cMPO. Our numerical calculations coincide with the analytic results of TFIM. In the end, we give a short discussion about the entanglement entropy of cMPO's ground state.

Switching plasticity in compensated ferrimagnetic multilayers for neuromorphic computing ^Hot!

Weihao Li(李伟浩), Xiukai Lan(兰修凯), Xionghua Liu(刘雄华), Enze Zhang(张恩泽), Yongcheng Deng(邓永城), and Kaiyou Wang(王开友)

Chin. Phys. B, 2022, 31 (11): 117106. DOI: 10.1088/1674-1056/ac89dd

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Current-induced multilevel magnetization switching in ferrimagnetic spintronic devices is highly pursued for the application in neuromorphic computing. In this work, we demonstrate the switching plasticity in Co/Gd ferrimagnetic multilayers where the binary states magnetization switching induced by spin-orbit toque can be tuned into a multistate one as decreasing the domain nucleation barrier. Therefore, the switching plasticity can be tuned by the perpendicular magnetic anisotropy of the multilayers and the in-plane magnetic field. Moreover, we used the switching plasticity of Co/Gd multilayers for demonstrating spike timing-dependent plasticity and sigmoid-like activation behavior. This work gives useful guidance to design multilevel spintronic devices which could be applied in high-performance neuromorphic computing.

Angle-dependent spin wave spectra of permalloy ring arrays Suggested by editors

Shuxuan Wu(吴书旋), Zengtai Zhu(朱增泰), Yunxu Ma(马云旭), Jinwu Wei(魏晋武), Senfu Zhang(张森富), Jianbo Wang(王建波), and Qingfang Liu(刘青芳)

Chin. Phys. B, 2022, 31 (11): 117505. DOI: 10.1088/1674-1056/ac8af9

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We investigated the angle-dependent spin wave spectra of permalloy ring arrays with the fixed outer diameter and various inner diameters by ferromagnetic resonance spectroscopy and micromagnetic simulation. When the field is obliquely applied to the ring, local resonance mode can be observed in different parts of the rings. And the resonance mode will change to perpendicular spin standing waves if the magnetic field is applied along the perpendicular direction. The simulation results demonstrated this evolution and implied more resonance modes that maybe exist. And the mathematical fitting results based on the Kittel equation further proved the existence of local resonance mode.

RNAGCN: RNA tertiary structure assessment with a graph convolutional network Suggested by editors

Chengwei Deng(邓成伟), Yunxin Tang(唐蕴芯), Jian Zhang(张建), Wenfei Li(李文飞), Jun Wang(王骏), and Wei Wang(王炜)

Chin. Phys. B, 2022, 31 (11): 118702. DOI: 10.1088/1674-1056/ac8ce3

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RNAs play crucial and versatile roles in cellular biochemical reactions. Since experimental approaches of determining their three-dimensional (3D) structures are costly and less efficient, it is greatly advantageous to develop computational methods to predict RNA 3D structures. For these methods, designing a model or scoring function for structure quality assessment is an essential step but this step poses challenges. In this study, we designed and trained a deep learning model to tackle this problem. The model was based on a graph convolutional network (GCN) and named RNAGCN. The model provided a natural way of representing RNA structures, avoided complex algorithms to preserve atomic rotational equivalence, and was capable of extracting features automatically out of structural patterns. Testing results on two datasets convincingly demonstrated that RNAGCN performs similarly to or better than four leading scoring functions. Our approach provides an alternative way of RNA tertiary structure assessment and may facilitate RNA structure predictions. RNAGCN can be downloaded from https://gitee.com/dcw-RNAGCN/rnagcn.

Riemann-Hilbert approach and N double-pole solutions for a nonlinear Schrödinger-type equation Suggested by editors

Guofei Zhang(张国飞), Jingsong He(贺劲松), and Yi Cheng(程艺)

Chin. Phys. B, 2022, 31 (11): 110201. DOI: 10.1088/1674-1056/ac7a1b

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We investigate the inverse scattering transform for the Schrödinger-type equation under zero boundary conditions with the Riemann-Hilbert (RH) approach. In the direct scattering process, the properties are given, such as Jost solutions, asymptotic behaviors, analyticity, the symmetries of the Jost solutions and the corresponding spectral matrix. In the inverse scattering process, the matrix RH problem is constructed for this integrable equation base on analyzing the spectral problem. Then, the reconstruction formula of potential and trace formula are also derived correspondingly. Thus, N double-pole solutions of the nonlinear Schrödinger-type equation are obtained by solving the RH problems corresponding to the reflectionless cases. Furthermore, we present a single double-pole solution by taking some parameters, and it is analyzed in detail.

Diffusion dynamics in branched spherical structure Suggested by editors

Kheder Suleiman, Xue-Lan Zhang(张雪岚), Sheng-Na Liu(刘圣娜), and Lian-Cun Zheng(郑连存)

Chin. Phys. B, 2022, 31 (11): 110202. DOI: 10.1088/1674-1056/ac7a16

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Diffusion on a spherical surface with trapping is a common phenomenon in cell biology and porous systems. In this paper, we study the diffusion dynamics in a branched spherical structure and explore the influence of the geometry of the structure on the diffusion process. The process is a spherical movement that occurs only for a fixed radius and is interspersed with a radial motion inward and outward the sphere. Two scenarios govern the transport process in the spherical cavity: free diffusion and diffusion under external velocity. The diffusion dynamics is described by using the concepts of probability density function (PDF) and mean square displacement (MSD) by Fokker-Planck equation in a spherical coordinate system. The effects of dead ends, sphere curvature, and velocity on PDF and MSD are analyzed numerically in detail. We find a transient non-Gaussian distribution and sub-diffusion regime governing the angular dynamics. The results show that the diffusion dynamics strengthens as the curvature of the spherical surface increases and an external force is exerted in the same direction of the motion.

Application of Galerkin spectral method for tearing mode instability

Wu Sun(孙武), Jiaqi Wang(王嘉琦), Lai Wei(魏来), Zhengxiong Wang(王正汹), Dongjian Liu(刘东剑), and Qiaolin He(贺巧琳)

Chin. Phys. B, 2022, 31 (11): 110203. DOI: 10.1088/1674-1056/ac600d

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Magnetic reconnection and tearing mode instability play a critical role in many physical processes. The application of Galerkin spectral method for tearing mode instability in two-dimensional geometry is investigated in this paper. A resistive magnetohydrodynamic code is developed, by the Galerkin spectral method both in the periodic and aperiodic directions. Spectral schemes are provided for global modes and local modes. Mode structures, resistivity scaling, convergence and stability of tearing modes are discussed. The effectiveness of the code is demonstrated, and the computational results are compared with the results using Galerkin spectral method only in the periodic direction. The numerical results show that the code using Galerkin spectral method individually allows larger time step in global and local modes simulations, and has better convergence in global modes simulations.

Dynamical behavior and optimal impulse control analysis of a stochastic rumor spreading model

Liang'an Huo(霍良安) and Xiaomin Chen(陈晓敏)

Chin. Phys. B, 2022, 31 (11): 110204. DOI: 10.1088/1674-1056/ac98fb

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The Internet era has brought great convenience to our life and communication. Meanwhile, it also makes a bunch of rumors propagate faster and causes even more harm to human life. Therefore, it is necessary to perform effective control mechanisms to minimize the negative social impact from rumors. Thereout, firstly, we formulate a rumor spreading model considering psychological factors and thinking time, then, we add white noise (i.e., stochastic interference) and two pulse control strategies which denote education mechanism and refutation mechanism into the model. Secondly, we obtain the global positive solutions and demonstrate the global exponential stability of the unique positive periodic rumor-free solution. Thirdly, we discuss the extinction and persistence of rumor. Moreover, we use Pontriagin's minimum principle to explore the optimal impulse control. Finally, several numerical simulations are carried out to verify the effectiveness and availability of the theoretical analysis. We conclude that the pulse control strategies have a great influence on controlling rumor spreading, and different control strategies should be adopted under different transmission scenarios.

Quantum routing of few photons using a nonlinear cavity coupled to two chiral waveguides

Jian-Shuang Liu(刘建双), Ya Yang(杨亚), Jing Lu(卢竞), and Lan Zhou(周兰)

Chin. Phys. B, 2022, 31 (11): 110301. DOI: 10.1088/1674-1056/ac7f8f

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We investigate few-photon scattering properties in two one-dimensional waveguides chirally coupled to a nonlinear cavity. The quantum states of scattered few photons are solved analytically via a real-space approach, and the solution indicates the few-photon reflection and transmission properties. When inputting two photons of equal energy to resonate with the cavity, the propagation characteristics of the two photons will be interesting, which is different from the previous anti-bunching effects with a quantum emitter. More importantly, when the total energy of the two incident photons equals the energy of a nonlinear cavity accommodating two photons, influence of the bound state will become larger to result in disappearance of antibunching effect. However, the bound state has no effect on probability of routing to another waveguide.

Spin current in a spinor Bose-Einstein condensate induced by a gradient magnetic field Suggested by editors

Li Tian(田丽), Ningxuan Zheng(郑宁宣), Jun Jian(蹇君), Wenliang Liu(刘文良), Jizhou Wu(武寄洲), Yuqing Li(李玉清), Yongming Fu(付永明), Peng Li(李鹏), Vladimir Sovkov, Jie Ma(马杰), Liantuan Xiao(肖连团), and Suotang Jia(贾锁堂)

Chin. Phys. B, 2022, 31 (11): 110302. DOI: 10.1088/1674-1056/ac80ac

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We develop a research of spin currents in a ²³Na spinor Bose-Einstein condensate (BEC) by applying a magnetic field gradient. The spin current is successfully induced by the spin-dependent force arising from the magnetic field gradient. The dynamics of the spin components under the magnetic force is investigated. The study is promising to be extended to produce a longer spin-coherence and to enhance the sensitivity of the spin-mixing interferometry in a spinor BEC.

Analysis of atmospheric effects on the continuous variable quantum key distribution

Tao Liu(刘涛), Shuo Zhao(赵硕), Ivan B. Djordjevic, Shuyu Liu(刘舒宇), Sijia Wang(王思佳), Tong Wu(吴彤), Bin Li(李斌), Pingping Wang(王平平), and Rongxiang Zhang(张荣香)

Chin. Phys. B, 2022, 31 (11): 110303. DOI: 10.1088/1674-1056/ac6b1f

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Atmospheric effects have significant influence on the performance of a free-space optical continuous variable quantum key distribution (CVQKD) system. In this paper, we investigate how the transmittance, excess noise and interruption probability caused by atmospheric effects affect the secret-key rate (SKR) of the CVQKD. Three signal wavelengths, two weather conditions, two detection schemes, and two types of attacks are considered in our investigation. An expression aims at calculating the interruption probability is proposed based on the Kolmogorov spectrum model. The results show that a signal using long working wavelength can propagate much further than that of using short wavelength. Moreover, as the wavelength increases, the influence of interruption probability on the SKR becomes more significant, especially within a certain transmission distance. Therefore, interruption probability must be considered for CVQKD by using long-signal wavelengths. Furthermore, different detection schemes used by the receiver will result in different transmission distances when subjected to individual attacks and collective attacks, respectively.

Topological superconductivity in Janus monolayer transition metal dichalcogenides Suggested by editors

Xian-Dong Li(李现东), Zuo-Dong Yu(余作东), Wei-Peng Chen(陈伟鹏), and Chang-De Gong(龚昌德)

Chin. Phys. B, 2022, 31 (11): 110304. DOI: 10.1088/1674-1056/ac8739

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The Janus monolayer transition metal dichalcogenides (TMDs) $MXY$ ($M={\rm Mo}$, W, $etc$. and $X, Y={\rm S}$, Se, $etc$.) have been successfully synthesized in recent years. The Rashba spin splitting in these compounds arises due to the breaking of out-of-plane mirror symmetry. Here we study the pairing symmetry of superconducting Janus monolayer TMDs within the weak-coupling framework near critical temperature $T_{\rm c}$, of which the Fermi surface (FS) sheets centered around both $ărGamma$ and $K (K')$ points. We find that the strong Rashba splitting produces two kinds of topological superconducting states which differ from that in its parent compounds. More specifically, at relatively high chemical potentials, we obtain a time-reversal invariant $s + f + p$-wave mixed superconducting state, which is fully gapped and topologically nontrivial, $i.e.$, a $\mathbb{Z}_2$ topological state. On the other hand, a time-reversal symmetry breaking $d + p + f$-wave superconducting state appears at lower chemical potentials. This state possess a large Chern number $|C|=6$ at appropriate pairing strength, demonstrating its nontrivial band topology. Our results suggest the Janus monolayer TMDs to be a promising candidate for the intrinsic helical and chiral topological superconductors.

Fringe visibility and correlation in Mach-Zehnder interferometer with an asymmetric beam splitter

Yan-Jun Liu(刘彦军), Mei-Ya Wang(王美亚), Zhong-Cheng Xiang(相忠诚), and Hai-Bin Wu(吴海滨)

Chin. Phys. B, 2022, 31 (11): 110305. DOI: 10.1088/1674-1056/ac8c3b

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We study the wave-particle duality in a general Mach-Zehnder interferometer with an asymmetric beam splitter from the viewpoint of quantum information theory. The correlations (including the classical correlation and the quantum correlation) between the particle and the which-path detector are derived when they are in pure state or mixed state at the output of Mach-Zehnder interferometer. It is found that the fringe visibility and the correlations are effected by the asymmetric beam splitter and the input state of the particle. The complementary relations between the fringe visibility and the correlations are also presented.

Passively stabilized single-photon interferometer

Hai-Long Liu(刘海龙), Min-Jie Wang(王敏杰), Jia-Xin Bao(暴佳鑫), Chao Liu(刘超), Ya Li(李雅), Shu-Jing Li(李淑静), and Hai Wang(王海)

Chin. Phys. B, 2022, 31 (11): 110306. DOI: 10.1088/1674-1056/ac597b

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A single-photon interferometer is a fundamental element in quantum information science. In most previously reported works, single-photon interferometers use an active feedback locking system to stabilize the relative phase between two arms of the interferometer. Here, we use a pair of beam displacers to construct a passively stable single-photon interferometer. The relative phase stabilization between the two arms is achieved by stabilizing the temperature of the beam displacers. A purely polarized single-photon-level pulse is directed into the interferometer input port. By analyzing and measuring the polarization states of the single-photon pulse at the output port, the achieved polarization fidelity of the interferometer is about 99.1 ±0.1%. Our passively stabilized single-photon interferometer provides a key element for generating high-fidelity entanglement between a photon and atomic memory.

Quantum speed limit for mixed states in a unitary system

Jie-Hui Huang(黄接辉), Li-Guo Qin(秦立国), Guang-Long Chen(陈光龙), Li-Yun Hu(胡利云), and Fu-Yao Liu(刘福窑)

Chin. Phys. B, 2022, 31 (11): 110307. DOI: 10.1088/1674-1056/ac76b4

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Since the evolution of a mixed state in a unitary system is equivalent to the joint evolution of the eigenvectors contained in it, we could use the tool of instantaneous angular velocity for pure states to study the quantum speed limit (QSL) of a mixed state. We derive a lower bound for the evolution time of a mixed state to a target state in a unitary system, which automatically reduces to the quantum speed limit induced by the Fubini-Study metric for pure states. The computation of the QSL of a degenerate mixed state is more complicated than that of a non-degenerate mixed state, where we have to make a singular value decomposition (SVD) on the inner product between the two eigenvector matrices of the initial and target states. By combing these results, a lower bound for the evolution time of a general mixed state is presented. In order to compare the tightness among the lower bound proposed here and lower bounds reported in the references, two examples in a single-qubit system and in a single-qutrit system are studied analytically and numerically, respectively. All conclusions derived in this work are independent of the eigenvalues of the mixed state, which is in accord with the evolution properties of a quantum unitary system.

Finite-time complex projective synchronization of fractional-order complex-valued uncertain multi-link network and its image encryption application Suggested by editors

Yong-Bing Hu(胡永兵), Xiao-Min Yang(杨晓敏), Da-Wei Ding(丁大为), and Zong-Li Yang(杨宗立)

Chin. Phys. B, 2022, 31 (11): 110501. DOI: 10.1088/1674-1056/ac7869

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Multi-link networks are universal in the real world such as relationship networks, transportation networks, and communication networks. It is significant to investigate the synchronization of the network with multi-link. In this paper, considering the complex network with uncertain parameters, new adaptive controller and update laws are proposed to ensure that complex-valued multilink network realizes finite-time complex projective synchronization (FTCPS). In addition, based on fractional-order Lyapunov functional method and finite-time stability theory, the criteria of FTCPS are derived and synchronization time is given which is associated with fractional order and control parameters. Meanwhile, numerical example is given to verify the validity of proposed finite-time complex projection strategy and analyze the relationship between synchronization time and fractional order and control parameters. Finally, the network is applied to image encryption, and the security analysis is carried out to verify the correctness of this method.

Interface modulated electron mobility enhancement in core-shell nanowires Suggested by editors

Yan He(贺言), Hua-Kai Xu(许华慨), and Gang Ouyang(欧阳钢)

Chin. Phys. B, 2022, 31 (11): 110502. DOI: 10.1088/1674-1056/ac7b1c

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The transport properties of core-shell nanowires (CSNWs) under interface modulation and confinement are investigated based on the atomic-bond-relaxation (ABR) correlation mechanism and Fermi's golden rule. An analytical expression for the relationship between carrier mobility and interface mismatch strain is derived and the influence of size, shell thickness and alloyed layer on effective mass, band structures, and deformation potential constant are studied. It is found that interface modulation can not only reduce the lattice mismatch to optimize the band alignment, but also participate in the carrier transport for enhancing mobility. Moreover, the underlying mechanism regarding the interface shape dependence of transport properties in CSNWs is clarified. The great enhancement of electron mobility suggests that the interface modulation may become a potential pathway to improving the performance of nanoelectronic devices.

An image encryption algorithm based on spatiotemporal chaos and middle order traversal of a binary tree

Yining Su(苏怡宁), Xingyuan Wang(王兴元), and Shujuan Lin(林淑娟)

Chin. Phys. B, 2022, 31 (11): 110503. DOI: 10.1088/1674-1056/ac6861

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This paper proposes an image encryption algorithm based on spatiotemporal chaos and middle order traversal of a binary tree. Firstly, other programming software is used to perform the middle order traversal, and the plaintext image is sorted according to the middle order traversal sequence on the permutation. Secondly, the chaotic sequence is generated using the coupled map lattice to set the chaotic interference value. Finally, the XOR operation between the adjacent pixel values of the replacement image is completed to generate the ciphertext matrix. The simulation and experimental results show that the proposed algorithm can resist typical attacks and has good robustness.

A spintronic memristive circuit on the optimized RBF-MLP neural network

Yuan Ge(葛源), Jie Li(李杰), Wenwu Jiang(蒋文武), Lidan Wang(王丽丹), and Shukai Duan(段书凯)

Chin. Phys. B, 2022, 31 (11): 110702. DOI: 10.1088/1674-1056/ac6b1d

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A radial basis function network (RBF) has excellent generalization ability and approximation accuracy when its parameters are set appropriately. However, when relying only on traditional methods, it is difficult to obtain optimal network parameters and construct a stable model as well. In view of this, a novel radial basis neural network (RBF-MLP) is proposed in this article. By connecting two networks to work cooperatively, the RBF's parameters can be adjusted adaptively by the structure of the multi-layer perceptron (MLP) to realize the effect of the backpropagation updating error. Furthermore, a genetic algorithm is used to optimize the network's hidden layer to confirm the optimal neurons (basis function) number automatically. In addition, a memristive circuit model is proposed to realize the neural network's operation based on the characteristics of spin memristors. It is verified that the network can adaptively construct a network model with outstanding robustness and can stably achieve 98.33% accuracy in the processing of the Modified National Institute of Standards and Technology (MNIST) dataset classification task. The experimental results show that the method has considerable application value.

Dynamic range and linearity improvement for zero-field single-beam atomic magnetometer

Kai-Feng Yin(尹凯峰), Ji-Xi Lu(陆吉玺), Fei Lu(逯斐), Bo Li(李博), Bin-Quan Zhou(周斌权), and Mao Ye(叶茂)

Chin. Phys. B, 2022, 31 (11): 110703. DOI: 10.1088/1674-1056/ac6010

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Zero-field single-beam atomic magnetometers with transverse parametric modulation for ultra-weak magnetic field detection have attracted widespread attention recently. In this study, we present a comprehensive response model and propose a modification method of conventional first harmonic response by introducing the second harmonic correction. The proposed modification method gives improvement in dynamic range and reduction of linearity error. Additionally, our modification method shows suppression of response instability caused by optical intensity and frequency fluctuations. An atomic magnetometer with single-beam configuration is built to compare the performance between our proposed method and the conventional method. The results indicate that our method's magnetic field response signal achieves a 5-fold expansion of dynamic range from 2 nT to 10 nT, with the linearity error decreased from 5% to 1%. Under the fluctuations of 5% for optical intensity and ±15 GHz detuning of frequency, the proposed modification method maintains intensity-related instability less than 1% and frequency-related instability less than 8% while the conventional method suffers 15% and 38%, respectively. Our method is promising for future high-sensitive and long-term stable optically pumped atomic sensors.

A single dual-mode gas sensor for early safety warning of Li-ion batteries: Micro-scale Li dendrite and electrolyte leakage

Wenjun Yan(闫文君), Zhishen Jin(金志燊), Zhengyang Lin(林政扬), Shiyu Zhou(周诗瑜), Yonghai Du(杜永海), Yulong Chen(陈宇龙), and Houpan Zhou(周后盘)

Chin. Phys. B, 2022, 31 (11): 110704. DOI: 10.1088/1674-1056/ac98a3

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Li dendrites and electrolyte leakage are common causes of Li-ion battery failure. H₂, generated by Li dendrites, and electrolyte vapors have been regarded as gas markers of the early safety warning of Li-ion batteries. SnO₂-based gas sensors, widely used for a variety of applications, are promising for the early safety detection of Li-ion batteries, which are necessary and urgently required for the development of Li-ion battery systems. However, the traditional SnO₂ sensor, with a single signal, cannot demonstrate intelligent multi-gas recognition. Here, a single dual-mode (direct and alternating current modes) SnO₂ sensor demonstrates clear discrimination of electrolyte vapors and H₂, released in different states of Li-ion batteries, together with principal component analysis (PCA) analysis. This work provides insight into the intelligent technology of single gas sensors.

A new global potential energy surface of the ground state of SiH₂⁺ (X²A₁) system and dynamics calculations of the Si⁺ + H₂ (v₀ = 2, j₀ = 0) → SiH⁺ + H reaction

Yong Zhang(张勇), Xiugang Guo(郭秀刚), and Haigang Yang(杨海刚)

Chin. Phys. B, 2022, 31 (11): 113101. DOI: 10.1088/1674-1056/ac7456

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A global potential energy surface (PES) of the ground state of SiH$_{2}^{+}$ system is built by using neural network method based on 18223 ab initio points. The topographic properties of PES are presented and compared with previous theoretical and experimental studies. The results indicate that the spectroscopic parameters obtained from the new PES are in good agreement with the experimental data. In order to further verify the validity of the new PES, a test dynamics calculation of the Si$^{+} +$ H$_{2}$ ($v_0 = 2, j_{0} = 0$) $\to $ H $+$ SiH$^{+}$ reaction has been carried out by using the time-dependent wave packet method. The integral cross sections and rate constants are computed for the title reaction. The reasonable dynamical behavior indicates that the newly constructed PES is suitable for relevant dynamics investigations.

Ultra-wideband surface plasmonic bandpass filter with extremely wide upper-band rejection

Xue-Wei Zhang(张雪伟), Shao-Bin Liu(刘少斌), Qi-Ming Yu(余奇明), Ling-Ling Wang(王玲玲), Kun Liao(廖昆), and Jian Lou(娄健)

Chin. Phys. B, 2022, 31 (11): 114101. DOI: 10.1088/1674-1056/ac6015

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An ultra-wideband bandpass filter (BPF) with a wide out-of-band rejection based on a surface plasmonic waveguide (SPW) slotline with ring grooves is designed and analyzed. A paired microstrip-to-slotline transition is designed for quasi-TEM to TM mode conversion by using a microstrip line with a circular pad and the slotline with the same circular slot. The mode conversion between the TM and the surface plasmon polariton (SPP) mode is realized by using a gradient slotline with ring grooves and an impedance matching technique. The upper cut-off frequencies of the passband can be adjusted by using these proposed SPP units, while the lower frequencies of the passband are created by using the microstrip-to-slotline transitions to give an ultra-wideband BPF. The dispersion curves of SPP units, electric field distribution, and the transmission spectra of the proposed ultra-wideband bandpass filter are all calculated and analyzed by the finite-difference time-domain (FDTD) method. The simulated results show that the presented filter has good performance including a wide 3-dB bandwidth of 149% from 0.57 GHz to 3.93 GHz, an extremely wide 40-dB upper-band rejection from 4.2 GHz to 18.5 GHz, and low loss and high selectivity in the passband. To prove the design validity, a prototype of the BPF has been manufactured and measured, showing a reasonable agreement with simulation results. The unique features of the proposed BPF may make it applicable for integrated circuit and plasmonic devices in microwave or THz frequency ranges.

Switchable vortex beam polarization state terahertz multi-layer metasurface Suggested by editors

Min Zhong(仲敏) and Jiu-Sheng Li(李九生)

Chin. Phys. B, 2022, 31 (11): 114201. DOI: 10.1088/1674-1056/ac7cd2

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We propose a switchable vortex beam polarization state terahertz multi-layer metasurface, which consists of three-layer elliptical metal crosses, four-layer dielectrics, and two-layer hollow metal circles, which are alternately superimposed. Under the normal incidence of left-handed circularly polarized (LCP) wave and the right-handed circularly polarized (RCP) waves, the proposed structure realizes three independent control functions, i.e., focused and vortex beam, vortex beam with different topological charges, and polarization states switching, and azimuth switching of two vortex beams with different polarization states. The results show that the proposed metasurface provides a new idea for investigating the multifunctional terahertz wave modulation devices.

Full color ghost imaging by using both time and code division multiplexing technologies Suggested by editors

Le Wang(王乐), Hui Guo(郭辉), and Shengmei Zhao(赵生妹)

Chin. Phys. B, 2022, 31 (11): 114202. DOI: 10.1088/1674-1056/ac7e33

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We propose a new full color ghost imaging scheme using both time and code division multiplexing technologies. In the scheme, the speckle patterns of three colors (red, green and blue) are modulated with different time slots and codes. The light intensity is sampled by one bucket detector. Then based on the modulated time slots and codes, we can effectively and simultaneously extract three detection component signals corresponding to three color components of objects from the sampling signal of the bucket detector. Finally, three component images resulting from the three component detection signals can be synthesized into a full color image. The experimental results verify the feasibility of our scheme under the limit of the number of time slots and codes. Moreover, our scheme reduces the number of bucket detectors and can realize high quality imaging even in a noisy environment.

Optical properties of He⁺-implanted and diamond blade-diced terbium gallium garnet crystal planar and ridge waveguides

Jia-Li You(游佳丽), Yu-Song Wang(王雨松), Tong Wang(王彤), Li-Li Fu(付丽丽), Qing-Yang Yue(岳庆炀), Xiang-Fu Wang(王祥夫), Rui-Lin Zheng(郑锐林), and Chun-Xiao Liu(刘春晓)

Chin. Phys. B, 2022, 31 (11): 114203. DOI: 10.1088/1674-1056/ac7c02

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Terbium gallium garnet (Tb₃Ga₅O₁₂, TGG) crystal can be used to fabricate various magneto-optical devices due to its optimal Faraday effect. In this work, 400-keV He⁺ ions with a fluence of 6.0×10¹⁶ ions/cm² are irradiated into the TGG crystal for the planar waveguide formation. The precise diamond blade dicing with a rotation speed of 2×10⁴ rpm and a cutting velocity of 0.1 mm/s is performed on the He⁺-implanted TGG planar waveguide for the ridge structure. The dark-mode spectrum of the He⁺-implanted TGG planar waveguide is measured by the prism-coupling method, thereby obtaining the relationship between the reflected light intensity and the effective refractive index. The refractive index profile of the planar waveguide is reconstructed by the reflectivity calculation method. The near-field light intensity distribution of the planar waveguide and the ridge waveguide are recorded by the end-face coupling method. The He⁺-implanted and diamond blade-diced TGG crystal planar and ridge waveguides are promising candidates for integrated magneto-optical devices.

Experimental demonstration of a fast calibration method for integrated photonic circuits with cascaded phase shifters ^Hot!

Junqin Cao(曹君勤), Zhixin Chen(陈志歆), Yaxin Wang(王亚新), Tianfeng Feng(冯田峰), Zhihao Li(李志浩), Zeyu Xing(邢泽宇), Huashan Li(李华山), and Xiaoqi Zhou(周晓祺)

Chin. Phys. B, 2022, 31 (11): 114204. DOI: 10.1088/1674-1056/ac8737

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With the development of research on integrated photonic quantum information processing, the integration level of the integrated quantum photonic circuits has been increasing continuously, which makes the calibration of the phase shifters on the chip increasingly difficult. For the calibration of multiple cascaded phase shifters that is not easy to be decoupled, the resources consumed by conventional brute force methods increase exponentially with the number of phase shifters, making it impossible to calibrate a relatively large number of cascaded phase shifters. In this work, we experimentally validate an efficient method for calibrating cascaded phase shifters that achieves an exponential increase in calibration efficiency compared to the conventional method, thus solving the calibration problem for multiple cascaded phase shifters. Specifically, we experimentally calibrate an integrated quantum photonic circuit with nine cascaded phase shifters and achieve a high-precision calibration with an average fidelity of 99.26%.

Yb:CaF₂–YF₃ transparent ceramics ultrafast laser at dual gain lines Suggested by editors

Xiao-Qin Liu(刘晓琴), Qian-Qian Hao(郝倩倩), Jie Liu(刘杰), Dan-Hua Liu(刘丹华), Wei-Wei Li(李威威), and Liang-Bi Su(苏良碧)

Chin. Phys. B, 2022, 31 (11): 114205. DOI: 10.1088/1674-1056/ac720f

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Yb³⁺:CaF₂-YF₃ transparent ceramics with excellent optical quality was successfully fabricated by hot-pressed method. Pulsed laser properties of this ceramics were investigated for the first time. Laser diode (LD) was applied as the pump source to generate a dual-wavelength mode-locked (ML) laser. The maximum average output power was 310 mW, which represents the highest output power of ultrafast calcium fluoride ceramic laser. The spectrum separated at 1048.9 nm and 1049.7 nm with a total pulse duration of 8.9 ps. The interval period between the beating signals was about 4.3 ps, corresponding to a 0.23 THz beat pulse repetition rate. These results demonstrate its potential in producing dual-wavelength ultrashort pulses. These Yb³⁺:CaF₂-YF₃ ceramics with low-cost and short-preparation period are ideal candidate materials for ultrafast lasers.

Microwave absorption properties regulation and bandwidth formula of oriented Y₂Fe₁₇N_3-δ@SiO₂/PU composite synthesized by reduction-diffusion method ^Hot!

Hao Wang(王浩), Liang Qiao(乔亮), Zu-Ying Zheng(郑祖应), Hong-Bo Hao(郝宏波), Tao Wang(王涛), Zheng Yang(杨正), and Fa-Shen Li(李发伸)

Chin. Phys. B, 2022, 31 (11): 114206. DOI: 10.1088/1674-1056/ac81ac

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As concepts closely related to microwave absorption properties, impedance matching and phase matching were rarely combined with material parameters to regulate properties and explore related mechanisms. In this work, reduction-diffusion method was innovatively applied to synthesize rare earth alloy Y$_{2}$Fe$_{17}$. In order to regulate the electromagnetic parameters of absorbers, the Y$_{2}$Fe$_{17}$N$_{3-\delta }$ particles were coated with silica (Y$_{2}$Fe$_{17}$N$_{3-\delta }$@SiO$_{2}$) and absorbers with different volume fractions were prepared. The relationship between impedance matching, matching thickness, and the strongest reflection loss peak (${\rm RL}_{\rm min}$) was presented obviously. Compared to the microwave absorption properties of Y$_{2}$Fe$_{17}$N$_{3-\delta }$/PU absorber, Y$_{2}$Fe$_{17}$N$_{3-\delta }$@SiO$_{2}$/PU absorbers are more conducive to the realization of microwave absorption material standards which are thin thickness, light weight, strong absorbing intensity, and broad bandwidth. Based on microwave frequency bands, the microwave absorption properties of the absorbers were analyzed and the related parameters were listed. As an important parameter related to perfect matching, reflection factor ($\sqrt {ărepsilon_{\rm r}/\mu_{\rm r}}$) was discussed combined with microwave amplitude attenuation. According to the origin and mathematical model of bandwidth, the formula of EAB (${\rm RL}<-10$ dB) was derived and simplified. The calculated bandwidths agreed well with experimental results.

Coupling characteristics of laterally coupled gratings with slots

Kun Tian(田锟), Yonggang Zou(邹永刚), Linlin Shi(石琳琳), He Zhang(张贺), Yingtian Xu(徐英添), Jie Fan(范杰), Hui Tang(唐慧), and Xiaohui Ma(马晓辉)

Chin. Phys. B, 2022, 31 (11): 114208. DOI: 10.1088/1674-1056/ac5c30

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Laterally-coupled ridge-waveguide distributed feedback lasers fabricated without epitaxial regrowth steps have the advantages of process simplification and low cost. We present a laterally coupled grating with slots. The slots etched between the ridge and grating area are designed to suppress the lateral diffusion of carriers and to reduce the influence of the aspect-ratio-dependent-etching effect on the grating morphology in the etching process. Moreover, the grating height in this structure can be decreased to lower the aspect ratio significantly, which is advantageous over the conventional laterally coupled ridge waveguide gratings. The effects of five main structural parameters on the coupling characteristics of gratings are studied by MODE Solutions. It is found that varying the lateral width of the grating can be used as an effective way to tune the coupling strength; narrow slots (100 nm and 300 nm) and wide ridge (2 μm-4 μm) promote the stability of grating coupling coefficient and device performance. It is important to note that the grating bottom should be fabricated precisely. The comparative study of carrier distribution and mode field distribution shows that the introduction of narrow slots can strengthen the competitive advantage and stability of the fundamental mode.

Yield enhancement of elliptical high harmonics driven by bicircular laser pulses

Xiaofan Zhang(张晓凡) and Xiaosong Zhu(祝晓松)

Chin. Phys. B, 2022, 31 (11): 114209. DOI: 10.1088/1674-1056/ac685b

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We theoretically investigate the yield enhancement of elliptical high harmonics in the interaction of molecules with bicircular laser pulses by solving the time-dependent Schrödinger equation. It is shown that by adjusting the relative intensity ratio of the two bicircular field components in specific ranges the yield of the molecular high harmonics for the plateau and cutoff regions can be respectively enhanced. To analyze this enhancement phenomenon, we calculate the weights of the electron classical trajectories. Additionally, we also study the ellipticity distribution of harmonics for different intensity ratios. We find that these enhanced harmonics are elliptically polarized, which we mainly attribute to the recombination dipole moment of the major weighted trajectories. These enhanced elliptical extreme ultraviolet and soft x-ray radiations may serve as essential tools for exploring the ultrafast dynamics in magnetic materials and chiral media.

An improved lumped parameter model predicting attenuation of earmuff with air leakage

Xu Zhong(仲旭), Zhe Chen(陈哲), and Dong Zhang(章东)

Chin. Phys. B, 2022, 31 (11): 114301. DOI: 10.1088/1674-1056/ac6b20

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Since air leakage is inevitable when earmuffs are worn improperly or together with safety glasses in factory or military, it is required to be considered to accurately predict earmuff attenuation. Besides unwanted air leakage, under controlled air leakage is introduced to earmuff to achieve adjustable attenuations in different signal-to-noise ratios (SNRs) and balance between attenuation and speech intelligibility. This work is to develop an improved lumped parameter model (LPM) to predict earmuff attenuation with consideration of air leakage. Air leakage paths are introduced into conventional LPM without air leakage, and air leakage path impedance is analytically described by Maa's microperforated tube impedance. Earmuff passive attenuation behavior can be analytically described and analyzed with the improved LPM. Finally, the validity of improved LPM is verified experimentally. The results indicate that the improved LPM can predict earmuff attenuation with air leakage, and air leakage deteriorates earmuff attenuation and turns resonance frequency higher.

Effects of mesoscale eddies on the spatial coherence of a middle range sound field in deep water Suggested by editors

Fei Gao(高飞), Fang-Hua Xu(徐芳华), and Zheng-Lin Li(李整林)

Chin. Phys. B, 2022, 31 (11): 114302. DOI: 10.1088/1674-1056/ac6014

Abstract ( 299 )

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Mesoscale eddies have a remarkable influence on the underwater sound field. Many previous studies have investigated the effects of eddies on transmission loss, the convergence zone, time delay, etc. However, the effects of eddies on spatial coherence are less well studied and remain unclear. In this paper, the effects of eddies on spatial coherence at the subsurface in deep water are investigated. The eddy environments are simulated with Gaussian eddy equations, the complex pressure field is obtained using a range-dependent parabolic equation model and the associated mechanism is analyzed based on ray theory and models. The results show that cold/warm mesoscale eddies affect spatial coherence in a high-intensity zone by changing the locations and width of the convergence zone. In the shadow zone, the horizontal correlation radius and the vertical correlation radius increase with range and decrease with depth, and they are increased by warm eddies and decreased by cold eddies, mainly caused by variation of the multipath structure.

Tuning infrared absorption in hyperbolic polaritons coated silk fibril composite Suggested by editors

Lihong Shi(史丽弘) and Jiebin Peng(彭洁彬)

Chin. Phys. B, 2022, 31 (11): 114401. DOI: 10.1088/1674-1056/ac8cdc

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Advanced textiles for thermal management give rise to many functional applications and unveil a new frontier for the study of human thermal comfort. Manipulating the coated quasi-particles between the composite components offers a platform to study the advanced thermoregulatory textiles. Here, we propose that coating the hyperbolic polariton can be an effective tool to tune infrared absorption in hexagonal boron nitride-coated silk composite. Remarkably, we achieve significant tuning of the infrared absorption efficiency of silk fibrils through the designed hexagonal boron nitride film. The underlying mechanism is related to resonance coupling between hyperbolic phonon polaritons. We find a notably high infrared absorption efficiency, nearly 3 orders larger than that without hBN coating, which can be achieved in our composite system. Our results indicate the promising future of advanced polariton-coated textiles and open a pathway to guide the artificial-intelligence design of advanced functional textiles.

Rolling velocity and relative motion of particle detector in local granular flow

Ran Li(李然), Bao-Lin Liu(刘宝林), Gang Zheng(郑刚), and Hui Yang(杨晖)

Chin. Phys. B, 2022, 31 (11): 114501. DOI: 10.1088/1674-1056/ac7dc0

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The velocity of a particle detector in granular flow can be regarded as the combination of rolling and sliding velocities. The study of the contribution of rolling velocity and sliding velocity provides a new explanation to the relative motion between the detector and the local granular flow. In this study, a spherical detector using embedded inertial navigation technology is placed in the chute granular flow to study the movement of the detector relative to the granular flow. It is shown by particle image velocimetry (PIV) that the velocity of chute granular flow conforms to Silbert's formula. And the velocity of the detector is greater than that of the granular flow around it. By decomposing the velocity into sliding and rolling velocity, it is indicated that the movement of the detector relative to the granular flow is mainly caused by rolling. The rolling detail shown by DEM simulation leads to two potential mechanisms based on the position and drive of the detector.

A study of cavitation nucleation in pure water using molecular dynamics simulation

Hua Xie(谢华), Yuequn Xu(徐跃群), and Cheng Zhong(钟成)

Chin. Phys. B, 2022, 31 (11): 114701. DOI: 10.1088/1674-1056/ac588a

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To discover the microscopic mechanism responsible for cavitation nucleation in pure water, nucleation processes in pure water are simulated using the molecular dynamics method. Cavitation nucleation is generated by uniformly stretching the system under isothermal conditions, and the formation and development of cavitation nuclei are simulated and discussed at the molecular level. The processes of energy, pressure, and density are analyzed, and the tensile strength of the pure water and the critical volume of the bubble nuclei are investigated. The results show that critical states exist in the process of cavitation nucleation. In the critical state, the energy, density, and pressure of the system change abruptly, and a stable cavitation nucleus is produced if the energy barrier is broken and the critical volume is exceeded. System pressure and water density are the key factors in the generation of cavitation nuclei. When the critical state is surpassed, the liquid is completely ruptured, and the volume of the cavitation nucleus rapidly increases to larger than 100 nm³; at this point, the surface tension of the bubble dominates the cavitation nucleus, instead of intermolecular forces. The negative critical pressure for bubble nucleation is -198.6 MPa, the corresponding critical volume is 13.84 nm³, and the nucleation rate is 2.42×10³² m^-3·^-1 in pure water at 300 K. Temperature has a significant effect on nucleation: as the temperature rises, nucleation thresholds decrease, and cavitation nucleation occurs earlier.

A theoretical investigation of glide dislocations in BN/AlN heterojunctions

Shujun Zhang(张淑君)

Chin. Phys. B, 2022, 31 (11): 116101. DOI: 10.1088/1674-1056/ac80aa

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Glide dislocations with periodic pentagon-heptagon pairs are investigated within the theory of one-dimensional misfit dislocations in the framework of an improved Peierls-Nabarro (P-N) equation in which the lattice discreteness is fully considered. We find an approximate solution to handle misfit dislocations, where the second-order derivative appears in the improved P-N equation. This result is practical for periodic glide dislocations with narrow width, and those in the BN/AlN heterojunction are studied. The structure of the misfit dislocations and adhesion work are obtained explicitly and verified by first-principles calculations. Compared with shuffle dislocations, the compression force in the tangential direction of glide dislocations has a greater impact on the normal direction, and the contributions of the normal displacement to the interfacial energy cannot simply be ignored.

Equal compressibility structural phase transition of molybdenum at high pressure

Lun Xiong(熊伦), Bin Li(李斌), Fang Miao(苗芳), Qiang Li (李强), Guangping Chen(陈光平), Jinxia Zhu(竹锦霞), Yingchun Ding(丁迎春), and Duanwei He(贺端威)

Chin. Phys. B, 2022, 31 (11): 116102. DOI: 10.1088/1674-1056/ac673a

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We have studied the high-pressure compression behavior of molybdenum up to 60 GPa by synchrotron radial x-ray diffraction (RXRD) in a diamond anvil cell (DAC). It is found that all diffraction peaks of molybdenum undergo a split at around 27 GPa, and we believe that a phase transition from a body-centered cubic structure to a rhombohedral structure at room pressure has occurred. The slope of pressure-volume curve shows continuity before and after this phase transition, when fitting the pressure-volume curves of the body-centered cubic structure at low pressure and the rhombohedral structure at high pressure. A bulk modulus of 261.3 (2.7) GPa and a first-order derivative of the bulk modulus of 4.15 (0.14) are obtained by using the nonhydrostatic compression data at the angle ψ = 54.7° between the diffracting plane normal and stress axis.

Pressure-induced novel structure with graphene-like boron-layer in titanium monoboride

Yuan-Yuan Jin(金园园), Jin-Quan Zhang(张金权), Shan Ling(凌山), Yan-Qi Wang(王妍琪), Song Li(李松), Fang-Guang Kuang(匡芳光), Zhi-Yan Wu(武志燕), and Chuan-Zhao Zhang(张传钊)

Chin. Phys. B, 2022, 31 (11): 116104. DOI: 10.1088/1674-1056/ac9222

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The recent discovery of the novel boron-framework in boron-rich metal borides with complex structures and intriguing features under high pressure has stimulated the search into the unique boron-network in the metal monoborides or boron-deficient metal borides at high pressure. Herein, based on the particle swarm optimization algorithm combined with first-principles calculations, we thoroughly explored the structural evolution and properties of TiB up to 200 GPa. This material undergoes a pressure-induced phase transition of $Pnma$ $\to $ $Cmcm$ $\to $ $Pmmm$. Besides of two known phases $Pnma$ and $Cmcm$, an unexpected orthorhombic $Pmmm$ structure was predicted to be energetically favored in the pressure range of 110.88-200 GPa. Intriguingly, the B covalent network eventually evolved from a one-dimensional zigzag chain in $Pnma$-TiB and $Cmcm$-TiB to a graphene-like B-sheet in $Pmmm$-TiB. On the basis of the microscopic hardness model, the calculated hardness ($H_{\rm v}$) values of $Pnma$ at 1 atm, $Cmcm$ at 100 GPa, and $Pmmm$ at 140 GPa are 36.81 GPa, 25.17 GPa, and 15.36 GPa, respectively. Remarkably, analyses of the density of states, electron localization function and the crystal orbital Hamilton population (COHP) exhibit that the bonding nature in the three TiB structures can be considered as a combination of the B-B and Ti-B covalent interactions. Moreover, the high hardness and excellent mechanical properties of the three TiB polymorphs can be ascribed to the strong B-B and Ti-B covalent bonds.

Lattice thermal conduction in cadmium arsenide Suggested by editors

R F Chinnappagoudra, M D Kamatagi, N R Patil, and N S Sankeshwar

Chin. Phys. B, 2022, 31 (11): 116301. DOI: 10.1088/1674-1056/ac7863

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Lattice thermal conductivity (LTC) of cadmium arsenide (Cd$_{3}$As$_{2}$) is studied over a wide temperature range (1-400 K) by employing the Callaway model. The acoustic phonons are considered to be the major carriers of heat and to be scattered by the sample boundaries, disorder, impurities, and other phonons via both Umklapp and normal phonon processes. Numerical calculations of LTC of Cd$_{3}$As$_{2}$ bring out the relative importance of the scattering mechanisms. Our systematic analysis of recent experimental data on thermal conductivity (TC) of Cd$_{3}$As$_{2}$ samples of different groups, presented in terms of LTC, $\kappa_{\scriptscriptstyle{\rm L}}$, using a nonlinear regression method, reveals good fits to the TC data of the samples considered for $T< \sim 50 $ K, and suggests a value of 0.2 for the Gruneisen parameter. It is, however, found that for $T> 100 $ K the inclusion of the electronic component of TC, $\kappa_{\rm e}$, incorporating contributions from relevant electron scattering mechanisms, is needed to obtain good agreement with the TC data over the wide temperature range. More detailed investigations of TC of Cd$_{3}$As$_{2}$ are required to better understand its suitability in thermoelectric and thermal management devices.

AA-stacked borophene-graphene bilayer as an anode material for alkali-metal ion batteries with a superhigh capacity Suggested by editors

Yi-Bo Liang(梁艺博), Zhao Liu(刘钊), Jing Wang(王静), and Ying Liu(刘英)

Chin. Phys. B, 2022, 31 (11): 116302. DOI: 10.1088/1674-1056/ac7859

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As the lightest two-dimensional material, monolayer borophene exhibits great potential as electrode materials, but it suffers from stability issues in the free-standing form. Here, the striped-borophene and graphene bilayer (sB/Gr) is found to be a high-performance anode material for rechargeable alkali-metal ion batteries. The first-principles results show that all the three alkali-metal atoms, Li, Na, and K, can be strongly adsorbed on sB/Gr with ultra-low diffusion barriers than that on pristine borophene/graphene, indicating good charge-discharge rates. Remarkably, high storage capacities are proposed for LIBs (1880 mA·h/g), NIBs (1648 mA·h/g), and KIBs (470 mA·h/g) with relatively small lattice change rate (<2.9%) in the process of alkali-metal atoms intercalations. These intriguing features of sB/Gr make it an excellent choice for batteries.

Graph dynamical networks for forecasting collective behavior of active matter

Yanjun Liu(刘彦君), Rui Wang(王瑞), Cai Zhao(赵偲), and Wen Zheng(郑文)

Chin. Phys. B, 2022, 31 (11): 116401. DOI: 10.1088/1674-1056/ac7cce

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After decades of theoretical studies, the rich phase states of active matter and cluster kinetic processes are still of research interest. How to efficiently calculate the dynamical processes under their complex conditions becomes an open problem. Recently, machine learning methods have been proposed to predict the degree of coherence of active matter systems. In this way, the phase transition process of the system is quantified and studied. In this paper, we use graph network as a powerful model to determine the evolution of active matter with variable individual velocities solely based on the initial position and state of the particles. The graph network accurately predicts the order parameters of the system in different scale models with different individual velocities, noise and density to effectively evaluate the effect of diverse condition. Compared with the classical physical deduction method, we demonstrate that graph network prediction is excellent, which could save significantly computing resources and time. In addition to active matter, our method can be applied widely to other large-scale physical systems.

Effects of B segregation on Mo-rich phase precipitation in S31254 super-austenitic stainless steels: Experimental and first-principles study

Pan-Pan Xu(徐攀攀), Jin-Yao Ma(马晋遥), Zhou-Hua Jiang(姜周华), Yi Zhang(张翊), Chao-Xiong Liang(梁超雄), Nan Dong(董楠), and Pei-De Han(韩培德)

Chin. Phys. B, 2022, 31 (11): 116402. DOI: 10.1088/1674-1056/ac744a

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Precipitation in super-austenitic stainless steels will significantly affect their corrosion resistance and hot workability. The effects of Cr and Mo on precipitation behaviors were mainly achieved by affecting the driving force for precipitation, especially Mo has a more substantial promotion effect on the formation of the σ phase than Cr. In the present study, B addition to the S31254 super-austenitic stainless steels shows an excellent ability to inhibit precipitation. The effect of B on the precipitation behaviors was investigated by microstructure characterization and theoretical calculations. The experimental observation shows that the small addition of B inhibits the formation of the σ phase along grain boundaries and changes from continuous to intermittent distribution. Moreover, the inhibitory effect increased obviously with the increase of B content. The influence of B addition was theoretically analyzed from the atomic level, and the calculation results demonstrate that B can inhibit the formation of σ phase precipitates by suppressing Mo migration to grain boundaries. It is found that B and Mo are inclined to segregate at Σ 5 and Σ 9 grain boundaries, with B showing the most severe grain boundary segregation tendency. While B distribution at the grain boundary before precipitation begins, the segregation of Mo and Cr will be restrained. Additionally, B's occupation will induce a high potential barrier, making it difficult for Mo to diffuse towards grain boundaries.

Enhanced photon emission by field emission resonances and local surface plasmon in tunneling junction

Jian-Mei Li(李健梅), Dong Hao(郝东), Li-Huan Sun(孙丽欢), Xiang-Qian Tang(唐向前), Yang An(安旸), Xin-Yan Shan(单欣岩), and Xing-Hua Lu(陆兴华)

Chin. Phys. B, 2022, 31 (11): 116801. DOI: 10.1088/1674-1056/ac8732

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We investigated the photon emission spectra on Ag (111) surface excited by tunneling electrons using a low temperature scanning tunneling microscope in ultrahigh vacuum. Characteristic plasmon modes were illustrated as a function of the bias voltage. The one electron excitation process was revealed by the linear relationship between the luminescence intensity and the tunneling current. Luminescence enhancement is observed in the tunneling regime for the relatively high bias voltages, as well as at the field emission resonance with bias voltage increased up to 9 V. Presence of a silver (Ag) nanoparticle in the tunneling junction results in an abnormally strong photon emission at the high field emission resonances, which is explained by the further enhancement due to coupling between the localized surface plasmon and the vacuum. The results are of potential value for applications where ultimate enhancement of photon emission is desired.

Robust and intrinsic type-III nodal points in a diamond-like lattice

Qing-Ya Cheng(程青亚), Yue-E Xie(谢月娥), Xiao-Hong Yan(颜晓红), and Yuan-Ping Chen(陈元平)

Chin. Phys. B, 2022, 31 (11): 117101. DOI: 10.1088/1674-1056/ac7c00

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An ideal type-III nodal point is generated by crossing a completely flat band and a dispersive band along a certain momentum direction. To date, the type-III nodal points found in two-dimensional (2D) materials have been mostly accidental and random rather than ideal cases, and no one mentions what kind of lattice can produce ideal nodal points. Here, we propose that ideal type-III nodal points can be obtained in a diamond-like lattice. The flat bands in the lattice originate from destructive interference of wavefunctions, and thus are intrinsic and robust. Moreover, the specific lattice can be realized in some 2D carbon networks, such as T-graphene and its derivatives. All the carbon structures possess type-III Dirac points. In two of the structures, consisting of triangular carbon rings, the type-III Dirac points are located just on the Fermi level and the Fermi surface is very clean. Our research not only opens a door to finding the ideal type-III Dirac points, but also provides 2D materials for exploring their physical properties experimentally.

Investigation of transport properties of perovskite single crystals by pulsed and DC bias transient current technique

Juan Qin(秦娟), Gang Cao(曹港), Run Xu(徐闰), Jing Lin(林婧), Hua Meng(孟华), Wen-Zhen Wang(王文贞), Zi-Ye Hong(洪子叶), Jian-Cong Cai(蔡健聪), and Dong-Mei Li(李冬梅)

Chin. Phys. B, 2022, 31 (11): 117102. DOI: 10.1088/1674-1056/ac7864

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Time-of-flight (ToF) transient current method is an important technique to study the transport characteristics of semiconductors. Here, both the direct current (DC) and pulsed bias ToF transient current method are employed to investigate the transport properties and electric field distribution inside the MAPbI$_{3}$ single crystal detector. Owing to the almost homogeneous electric field built inside the detector during pulsed bias ToF measurement, the free hole mobility can be directly calculated to be about 22 cm$^{2}\cdot$V$^{-1}\cdot$s$^{-1}$, and the hole lifetime is around 6.5 μs-17.5 μs. Hence, the mobility-lifetime product can be derived to be $1.4\times 10^{-4}$ cm$^{2}\cdot$V$^{-1}$-$3.9\times 10^{-4}$ cm$^{2}\cdot$V$^{-1}$. The transit time measured under the DC bias deviates with increasing voltage compared with that under the pulsed bias, which arises mainly from the inhomogeneous electric field distribution inside the perovskite. The positive space charge density can then be deduced to increase from 3.1$\times10^{10}$ cm$^{-3}$ to 6.89$\times 10^{10}$ cm$^{-3}$ in a bias range of 50 V-150 V. The ToF measurement can provide us with a facile way to accurately measure the transport properties of the perovskite single crystals, and is also helpful in obtaining a rough picture of the internal electric field distribution.

Quantum phase transitions in CePdAl probed by ultrasonic and thermoelectric measurements Suggested by editors

Hengcan Zhao(赵恒灿), Meng Lyu(吕孟), Jiahao Zhang(张佳浩), Shuai Zhang(张帅), and Peijie Sun(孙培杰)

Chin. Phys. B, 2022, 31 (11): 117103. DOI: 10.1088/1674-1056/ac8345

Abstract ( 245 )

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CePdAl has been recently recognized as a frustrated antiferromagnetic heavy-fermion compound with a pressure- or field-tuned, extended quantum critical phase at zero temperature. Identifying characteristic signatures of the emerging quantum critical phase, which are expected to be distinct from those near a quantum critical point, remains challenging. In this work, by performing ultrasonic and thermoelectric measurements down to very low temperatures in a ³He-⁴He dilution refrigerator in the presence of magnetic field, we are able to obtain some crucial thermodynamic and thermal transport features of the quantum critical phase, including a frustration-related elastic softening detected by ultrasound and a Fermi-surface change probed by thermoelectric effect.

Coherent interaction and action-counteraction theory in small polaron systems, and ground state properties

Zhi-Hua Luo(罗质华) and Chao-Fan Yu(余超凡)

Chin. Phys. B, 2022, 31 (11): 117104. DOI: 10.1088/1674-1056/ac67c1

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Based on the coherent interaction and action-counteraction principles, we investigate the ground state properties for small polaron systems, the coherent-squeezed fluctuation correction, and the anomalous lattice quantum fluctuation, with the new variational generator containing correlated squeezed-coherent coupling and quantum entanglement. Noting that $-2t $ is the T.B.A. energy, for the coherent interaction effect, we find the ground-state energy $E_0$ to be $-2.428t$, in which the coherent squeezed fluctuation correction $-A_0 t$ is $-0.463t $ (where $ t $ is the hopping integral, $\omega $ is the phonon frequency), with the electron-one-phonon coupling constant $g=$1 and the electron-two-phonon coupling constant $g_{1}=-0.1$. However, as a result of the action-counteraction effect, $\tilde{{E}}_{0} $ is $-2.788t$, but $-\tilde{{A}}_{0} t$ is $-0.735t$. As to the polaron binding energy $(E_{\rm P} )$, for the coherent interaction effect, $E_{\rm P} $ is $-1.38\omega $, but for the action-counteraction effect, $\tilde{{E}}_{\rm P}$ is $-1.88\omega $. In particular, the electron-two-phonon interaction noticeably enlarges the coherent interaction and the coherent squeezed quantum fluctuation correction. By intervening with the quantum entanglement, the evolutions of the squeezed coherent state and the lattice quantum fluctuation begin to take control. At that time, we encounter a new quantum phase coherence phenomenon — the collapse and revival of inversion repeatedly for the coherent state in the entangled evolution.

A novel Si-rich SiN bilayer passivation with thin-barrier AlGaN/GaN HEMTs for high performance millimeter-wave applications Suggested by editors

Zhihong Chen(陈治宏), Minhan Mi(宓珉瀚), Jielong Liu(刘捷龙), Pengfei Wang(王鹏飞), Yuwei Zhou(周雨威), Meng Zhang(张濛), Xiaohua Ma(马晓华), and Yue Hao(郝跃)

Chin. Phys. B, 2022, 31 (11): 117105. DOI: 10.1088/1674-1056/ac81a6

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We demonstrate a novel Si-rich SiN bilayer passivation technology for AlGaN/GaN high electron mobility transistors (HEMTs) with thin-barrier to minimize surface leakage current to enhance the breakdown voltage. The bilayer SiN with 20-nm Si-rich SiN and 100-nm Si$_{3}$N$_{4}$ was deposited by plasma-enhanced chemical vapor deposition (PECVD) after removing 20-nm SiO$_{2}$ pre-deposition layer. Compared to traditional Si$_{3}$N$_{4}$ passivation for thin-barrier AlGaN/GaN HEMTs, Si-rich SiN bilayer passivation can suppress the current collapse ratio from 18.54% to 8.40%. However, Si-rich bilayer passivation leads to a severer surface leakage current, so that it has a low breakdown voltage. The 20-nm SiO$_{2}$ pre-deposition layer can protect the surface of HEMTs in fabrication process and decrease Ga-O bonds, resulting in a lower surface leakage current. In contrast to passivating Si-rich SiN directly, devices with the novel Si-rich SiN bilayer passivation increase the breakdown voltage from 29 V to 85 V. Radio frequency (RF) small-signal characteristics show that HEMTs with the novel bilayer SiN passivation leads to $f_{\rm T}/f_{\rm max}$ of 68 GHz/102 GHz. At 30 GHz and $V_{\rm DS} = 20$ V, devices achieve a maximum $P_{\rm out}$ of 5.2 W/mm and a peak power-added efficiency (PAE) of 42.2%. These results indicate that HEMTs with the novel bilayer SiN passivation can have potential applications in the millimeter-wave range.

Electron tunneling through double-electric barriers on HgTe/CdTe heterostructure interface Suggested by editors

Liang-Zhong Lin(林亮中), Yi-Yun Ling(凌艺纭), Dong Zhang(张东), and Zhen-Hua Wu(吴振华)

Chin. Phys. B, 2022, 31 (11): 117201. DOI: 10.1088/1674-1056/ac7a0f

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We investigate theoretically the carrier transport in a two-dimensional topological insulator of (001) HgTe/CdTe quantum-well heterostructure with inverted band, and find distinct switchable features of the transmission spectra in the topological edge states by designing the double-electric modulation potentials. The transmission spectra exhibit the significant Fabry-Pérot resonances for the double-electric transport system. Furthermore, the transmission properties show rich behaviors when the Fermi energy lies in the different locations in the energy spectrum and the double-electric barrier regions. The opacity and transparency of the double-modulated barrier regions can be controlled by tuning the modulated potentials, Fermi energy and the length of modulated regions. This electrical switching behavior can be realized by tuning the voltages applied on the metal gates. The Fabry-Pérot resonances leads to oscillations in the transmission which can be observed in experimentally. This electric modulated-mechanism provides us a realistic way to switch the transmission in edge states which can be constructed in low-power information processing devices.

Fluorine-plasma treated AlGaN/GaN high electronic mobility transistors under off-state overdrive stress

Dongyan Zhao(赵东艳), Yubo Wang(王于波), Yanning Chen(陈燕宁), Jin Shao(邵瑾), Zhen Fu(付振), Fang Liu(刘芳), Yanrong Cao(曹艳荣), Faqiang Zhao(赵法强), Mingchen Zhong(钟明琛), Yasong Zhang(张亚松), Maodan Ma(马毛旦), Hanghang Lv(吕航航), Zhiheng Wang(王志恒), Ling Lv(吕玲), Xuefeng Zheng(郑雪峰), and Xiaohua Ma(马晓华)

Chin. Phys. B, 2022, 31 (11): 117301. DOI: 10.1088/1674-1056/ac81a7

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Influences of off-state overdrive stress on the fluorine-plasma treated AlGaN/GaN high-electronic mobility transistors (HEMTs) are experimentally investigated. It is observed that the reverse leakage current between the gate and source decreases after the off-state stress, whereas the current between the gate and drain increases. By analyzing those changes of the reverse currents based on the Frenkel-Poole model, we realize that the ionization of fluorine ions occurs during the off-state stress. Furthermore, threshold voltage degradation is also observed after the off-state stress, but the degradations of AlGaN/GaN HEMTs treated with different F-plasma RF powers are different. By comparing the differences between those devices, we find that the F-ions incorporated in the GaN buffer layer play an important role in averting degradation. Lastly, suggestions to obtain a more stable fluorine-plasma treated AlGaN/GaN HEMT are put forwarded.

Ozone oxidation of 4H-SiC and flat-band voltage stability of SiC MOS capacitors Suggested by editors

Zhi-Peng Yin(尹志鹏), Sheng-Sheng Wei(尉升升), Jiao Bai(白娇), Wei-Wei Xie(谢威威), Zhao-Hui Liu(刘兆慧), Fu-Wen Qin(秦福文), and De-Jun Wang(王德君)

Chin. Phys. B, 2022, 31 (11): 117302. DOI: 10.1088/1674-1056/ac7ccf

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We investigate the effect of ozone (O₃) oxidation of silicon carbide (SiC) on the flat-band voltage (V_fb) stability of SiC metal-oxide-semiconductor (MOS) capacitors. The SiC MOS capacitors are produced by O₃ oxidation, and their V_fb stability under frequency variation, temperature variation, and bias temperature stress are evaluated. Secondary ion mass spectroscopy (SIMS), atomic force microscopy (AFM), and x-ray photoelectron spectroscopy (XPS) indicate that O₃ oxidation can adjust the element distribution near SiC/SiO₂ interface, improve SiC/SiO₂ interface morphology, and inhibit the formation of near-interface defects, respectively. In addition, we elaborate the underlying mechanism through which O₃ oxidation improves the V_fb stability of SiC MOS capacitors by using the measurement results and O₃ oxidation kinetics.

Anisotropic plasmon dispersion and damping in multilayer 8-Pmmn borophene structures Suggested by editors

Kejian Liu(刘可鉴), Jian Li(李健), Qing-Xu Li(李清旭), and Jia-Ji Zhu(朱家骥)

Chin. Phys. B, 2022, 31 (11): 117303. DOI: 10.1088/1674-1056/ac6b2d

Abstract ( 239 )

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We investigate the collective plasma oscillations theoretically in multilayer 8-Pmmn borophene structures, where the tilted Dirac electrons in spatially separated layers are coupled via the Coulomb interaction. We calculate the energy dispersions and Landau dampings of the multilayer plasmon excitations as a function of the total number of layers, the interlayer separation, and the different orientations. Like multilayer graphene, the plasmon spectrum in multilayer borophene consists of one in-phase optical mode and N - 1 out-of-phase acoustical modes. We show that the plasmon modes possess kinks at the boundary of the interband single-particle continuum and the apparent anisotropic behavior. All the plasmon modes approach the same dispersion at a sufficiently large interlayer spacing in the short-wavelength limit. Especially along specific orientations, the optical mode could touch an energy maximum in the nondamping region, which shows non-monotonous behavior. Our work provides an understanding of the multilayer borophene plasmon and may pave the way for multilayer borophene-based plasmonic devices.

Interface engineering of transition metal dichalcogenide/GaN heterostructures: Modified broadband for photoelectronic performance ^Hot!

Yinlu Gao(高寅露), Kai Cheng(程开), Xue Jiang(蒋雪), and Jijun Zhao(赵纪军)

Chin. Phys. B, 2022, 31 (11): 117304. DOI: 10.1088/1674-1056/ac6eee

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The GaN-based heterostructures are widely used in optoelectronic devices, but the complex surface reconstructions and lattice mismatch greatly limit the applications. The stacking of two-dimensional transition metal dichalcogenide (TMD = MoS₂, MoSSe and MoSe₂) monolayers on reconstructed GaN surface not only effectively overcomes the larger mismatch, but also brings about novel electronic and optical properties. By adopting the reconstructed GaN (0001) surface with adatoms (N-ter GaN and Ga-ter GaN), the influences of complicated surface conditions on the electronic properties of heterostructures have been investigated. The passivated N-ter and Ga-ter GaN surfaces push the mid-gap states to the valence bands, giving rise to small bandgaps in heterostructures. The charge transfer between Ga-ter GaN surface and TMD monolayers occurs much easier than that across the TMD/N-ter GaN interfaces, which induces stronger interfacial interaction and larger valence band offset (VBO). The band alignment can be switched between type-I and type-II by assembling different TMD monolayers, that is, MoS₂/N-ter GaN and MoS₂/Ga-ter GaN are type-II, and the others are type-I. The absorption of visible light is enhanced in all considered TMD/reconstructed GaN heterostructures. Additionally, MoSe₂/Ga-ter GaN and MoSSe/N-ter GaN have larger conductor band offset (CBO) of 1.32 eV and 1.29 eV, respectively, extending the range from deep ultraviolet to infrared regime. Our results revel that the TMD/reconstructed GaN heterostructures may be used for high-performance broadband photoelectronic devices.

Steady-state and transient electronic transport properties of β-(Al_xGa_1-x)₂O₃/Ga₂O₃ heterostructures: An ensemble Monte Carlo simulation

Yan Liu(刘妍), Ping Wang(王平), Ting Yang(杨婷), Qian Wu(吴茜), Yintang Yang(杨银堂), and Zhiyong Zhang(张志勇)

Chin. Phys. B, 2022, 31 (11): 117305. DOI: 10.1088/1674-1056/ac7290

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The steady-state and transient electron transport properties of $\beta $-(Al$_{x}$Ga$_{1-x}$)$_{2}$O$_{3}$/Ga$_{2}$O$_{3}$ heterostructures were investigated by Monte Carlo simulation with the classic three-valley model. In particular, the electronic band structures were acquired by first-principles calculations, which could provide precise parameters for calculating the transport properties of the two-dimensional electron gas (2DEG), and the quantization effect was considered in the $\varGamma $ valley with the five lowest subbands. Wave functions and energy eigenvalues were obtained by iteration of the Schrödinger-Poisson equations to calculate the 2DEG scattering rates with five main scattering mechanisms considered. The simulated low-field electron mobilities agree well with the experimental results, thus confirming the effectiveness of our models. The results show that the room temperature electron mobility of the $\beta $-(Al$_{0.188}$Ga$_{0.812}$)$_{2}$O$_{3}$/Ga$_{2}$O$_{3}$ heterostructure at 10 kV$ \cdot$cm$^{-1}$ is approximately 153.669 cm$^{2}\cdot$V$^{-1}\cdot$s$^{-1}$, and polar optical phonon scattering would have a significant impact on the mobility properties at this time. The region of negative differential mobility, overshoot of the transient electron velocity and negative diffusion coefficients are also observed when the electric field increases to the corresponding threshold value or even exceeds it. This work offers significant parameters for the $\beta$-(Al$_{x}$Ga$_{1-x}$)$_{2}$O$_{3}$/Ga$_{2}$O$_{3}$ heterostructure that may benefit the design of high-performance $\beta$-(Al$_{x}$Ga$_{1-x}$)$_{2}$O$_{3}$/Ga$_{2}$O$_{3}$ heterostructure-based devices.

Growth and characterization of superconducting Ca_1-xNa_xFe₂As₂ single crystals by NaAs-flux method

Hong-Lin Zhou(周宏霖), Yu-Hao Zhang(张与豪), Yang Li(李阳), Shi-Liang Li(李世亮), Wen-Shan Hong(洪文山), and Hui-Qian Luo(罗会仟)

Chin. Phys. B, 2022, 31 (11): 117401. DOI: 10.1088/1674-1056/ac834a

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High-quality superconducting Ca$_{1-x}$Na$_x$Fe$_2$As$_2$ single crystals have been successfully grown by the NaAs-flux method, with sodium doping level $x = 0.4$-0.64. The typical sizes of these crystals are more than 10 mm in $ab$-plane and $\sim 0.1$ mm along $c$-axis in thickness. X-ray diffraction, resistance and magnetization measurements are carried out to characterize the quality of these crystals. While no signature of magnetic phase transitions is detected in the normal state, bulk superconductivity is found for these samples, with a sharp transition at $T_{\rm c}$ ranging from 19.8 K ($x = 0.4$) to 34.8 K ($x = 0.64$). The doping dependences of the $c$-axis parameter and $T_{\rm c}$ are consistent with previous reports, suggesting a possible connection between the lattice parameters and superconductivity.

Optical study on topological superconductor candidate Sr-doped Bi₂Se₃ ^Hot!

Jialun Liu(刘佳伦), Chennan Wang(王晨南), Tong Lin(林桐), Liye Cao(曹立叶), Lei Wang(王蕾), Jiaji Li(李佳吉), Zhen Tao(陶镇), Nan Shen(申娜), Rina Wu(乌日娜), Aifang Fang(房爱芳), Nanlin Wang(王楠林), and Rongyan Chen(陈荣艳)

Chin. Phys. B, 2022, 31 (11): 117402. DOI: 10.1088/1674-1056/ac7a10

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Utilizing infrared spectroscopy, we study the charge dynamics of the topological superconductor candidate Sr$_x$Bi$_2$Se$_3$. The frequency-dependent reflectivity $R(\omega$) demonstrates metallic feature and the scattering rate of the free carriers decreases with temperature decreasing. The plasma edge shows a slight blue shift upon cooling, similar to the behavior of Cu$_x$Bi$_2$Se$_3$. As the carrier concentration $n$ obtained by Hall resistivity increases slightly with the decreasing temperature, the effective mass is proved to increase as well, which is in contrast with that of Cu$_x$Bi$_2$Se$_3$.We also perform the ultrafast pump-probe study on the Sr$_{0.2}$Bi$_2$Se$_3$ compounds. Resembling its parent compound Bi$_2$Se$_3$, three distinct relaxation processes are found to contribute to the transient reflectivity. However, the deduced relaxation times are quite different. In addition, the electron-optical-phonon coupling constant is identified to be $\lambda = 0.88$.

Strain-modulated anisotropic Andreev reflection in a graphene-based superconducting junction

Xingfei Zhou(周兴飞), Ziming Xu (许子铭), Deliang Cao(曹德亮), and Fenghua Qi(戚凤华)

Chin. Phys. B, 2022, 31 (11): 117403. DOI: 10.1088/1674-1056/ac7553

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We investigate the Andreev reflection across a uniaxial strained graphene-based superconducting junction. Compared with pristine graphene-based superconducting junction, three opposite properties are found. Firstly, in the regime of the interband conversion of electron-hole, the Andreev retro-reflection happens. Secondly, in the regime of the intraband conversion of electron-hole, the specular Andreev reflection happens. Thirdly, the perfect Andreev reflection, electron-hole conversion with unit efficiency, happens at a nonzero incident angle of electron. These three exotic properties arise from the strain-induced anisotropic band structure of graphene, which breaks up the original relation between the direction of velocity of particle and the direction of the corresponding wavevector. Our finding gives an insight into the understanding of Andreev reflection and provides an alternative method to modulate the Andreev reflection.

Experimental observation of interlayer perpendicular standing spin wave mode with low damping in skyrmion-hosting [Pt/Co/Ta]₁₀ multilayer Suggested by editors

Zhen-Dong Chen(陈振东), Mei-Yang Ma(马眉扬), Sen-Fu Zhang(张森富), Mang-Yuan Ma(马莽原), Zi-Zhao Pan(潘咨兆), Xi-Xiang Zhang(张西祥), Xue-Zhong Ruan(阮学忠), Yong-Bing Xu(徐永兵), and Fu-Sheng Ma(马付胜)

Chin. Phys. B, 2022, 31 (11): 117501. DOI: 10.1088/1674-1056/ac7bf9

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An interlayer perpendicular standing spin wave mode is observed in the skyrmion-hosting [Pt/Co/Ta]₁₀ multilayer by measuring the time-resolved magneto-optical Kerr effect. The observed interlayer mode depends on the interlayer spin-pumping and spin transfer torque among the neighboring Co layers. This mode shows monotonically increasing frequency-field dependence which is similar to the ferromagnetic resonance mode, but within higher frequency range. Besides, the damping of the interlayer mode is found to be a relatively low constant value of 0.027 which is independent of the external field. This work expounds the potential application of the [heavy-metal/ferromagnetic-metal]_n multilayers to skyrmion-based magnonic devices which can provide multiple magnon modes, relatively low damping, and skyrmion states, simultaneously.

CrAlGe: An itinerant ferromagnet with strong tunability by heat treatment Suggested by editors

Zhaokun Dong(董昭昆), Zhen Wang(王振), Te Zhang(张特), Junsen Xiang(项俊森), Shuai Zhang(张帅), Lihua Liu(刘丽华), and Peijie Sun(孙培杰)

Chin. Phys. B, 2022, 31 (11): 117502. DOI: 10.1088/1674-1056/ac7858

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We present a comprehensive investigation on CrAlGe and realize that it is an itinerant ferromagnet with strong tunability of the Curie temperature $T_{\rm C}$ and the spontaneous moment $\mu_0$ depending on annealing heat treatment. While the value of $T_{\rm C}$ was previously reported to be 80 K with $\mu_0\approx$ 0.41$\mu_{\rm B}$, in this work the two quantities attain values as high as 170 K and 0.66$\mu_{\rm B}$, respectively. Heat treatment does not cause changes of the lattice parameters and symmetry, but results in a slight narrowing of the Bragg peaks. The strong tunability of the itinerant ferromagnetism indicates significantly tunable hybridization between the Cr 3d electrons and the conduction bands, in agreement with the dominant Cr-Al/Ge bonds of this compound. Further tuning along the same line towards even stronger or weaker itinerant ferromagnetism promises an interesting follow-up to clarify the localized-itinerant duality of the 3d electrons in this compound.

Magnetic properties and magnetocaloric effect in RE₅₅Co₃₀Al₁₀Si₅ (RE = Er and Tm) amorphous ribbons Suggested by editors

Hao Sun(孙浩), Junfeng Wang(王俊峰), Lu Tian(田路), Jianjian Gong(巩建建), Zhaojun Mo(莫兆军), Jun Shen(沈俊), and Baogen Shen(沈保根)

Chin. Phys. B, 2022, 31 (11): 117503. DOI: 10.1088/1674-1056/ac8733

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The magnetic and magnetocaloric effects (MCE) of the amorphous $RE_{55}$Co$_{30}$Al$_{10}$Si$_{5}$ ($RE={\rm Er}$ and Tm) ribbons were systematically investigated in this paper. Compounds with $R ={\rm Er}$ and Tm undergo a second-order magnetic phase transition from ferromagnetic (FM) to paramagnetic (PM) around Curie temperature $T_{\rm C} \sim 9.3$ K and 3 K, respectively. For Er$_{55}$Co$_{30}$Al$_{10}$Si$_{5}$ compound, an obvious magnetic hysteresis and thermal hysteresis were observed at low field below 6 K, possibly due to spin-glass behavior. Under the field change of 0 T-5 T, the maximum values of magnetic entropy change ($-\Delta S_{\rm M}^{\rm max}$) reach as high as 15.6 J/kg$\cdot$K and 15.7 J/kg$\cdot$K for Er$_{55}$Co$_{30}$Al$_{10}$Si$_{5}$ and Tm$_{55}$Co$_{30}$Al$_{10}$Si$_{5}$ compounds, corresponding refrigerant capacity (RC) values are estimated as 303 J/kg and 189 J/kg, respectively. The large MCE makes amorphous $RE_{55}$Co$_{30}$Al$_{10}$Si$_{5 }$ ($RE={\rm Er}$ and Tm) alloys become very attractive magnetic refrigeration materials in the low-temperature region.

Skyrmion transport driven by pure voltage generated strain gradient Suggested by editors

Shan Qiu(邱珊), Jia-Hao Liu(刘嘉豪), Ya-Bo Chen(陈亚博), Yun-Ping Zhao(赵云平), Bo Wei(危波), and Liang Fang(方粮)

Chin. Phys. B, 2022, 31 (11): 117701. DOI: 10.1088/1674-1056/ac8927

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The magnetic skyrmion transport driven by pure voltage-induced strain gradient is proposed and studied via micromagnetic simulation. Through combining the skyrmion with multiferroic heterojunction, a voltage-induced uniaxial strain gradient is adjusted to move skyrmions. In the system, a pair of short-circuited trapezoidal top electrodes can generate the symmetric strain. Due to the symmetry of strain, the magnetic skyrmion can be driven with a linear motion in the middle of the nanostrip without deviation. We calculate the strain distribution generated by the trapezoidal top electrodes pair, and further investigate the influence of the strain intensity as well as the strain gradient on the skyrmion velocity. Our findings provide a stable and low-energy regulation method for skyrmion transport.

A pure dielectric metamaterial absorber with broadband and thin thickness based on a cross-hole array structure

Wenbo Cao(曹文博), Youquan Wen(温又铨), Chao Jiang(姜超), Yantao Yu(余延涛), Yiyu Wang(王艺宇), Zheyipei Ma(麻哲乂培), Zixiang Zhao(赵子翔), Lanzhi Wang(王兰志), and Xiaozhong Huang(黄小忠)

Chin. Phys. B, 2022, 31 (11): 117801. DOI: 10.1088/1674-1056/ac6492

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A pure dielectric metamaterial absorber with broadband and thin thickness is proposed, whose structure is designed as a periodic cross-hole array. The pure dielectric metamaterial absorber with high permittivity is prepared by ceramic reinforced polymer composites. Compared with those with low permittivity, the absorber with high permittivity is more sensitive to structural parameters, which means that it is easier to optimize the equivalent electromagnetic parameters and achieve wide impedance matching by altering the size or shape of the unit cell. The optimized metamaterial absorber exhibits reflection loss below -10 dB in 7.93 GHz-35.76 GHz with a thickness of 3.5 mm, which shows favorable absorption properties under the oblique incidence of TE polarization (±45°). Whether it is a measured or simulated value, the strongest absorbing peak reaches below -45 dB, which exceeds that of most metamaterial absorbers. The distributions of power loss density and electric and magnetic fields are investigated to study the origin of their strong absorbing properties. Multiple resonance mechanisms are proposed to explain the phenomenon, including polarization relaxation of the dielectric and edge effects of the cross-hole array. This work overcomes the shortcomings of the narrow absorbing bandwidth of dielectrics. It demonstrates that the pure dielectric metamaterial absorber with high permittivity has great potential in the field of microwave absorption.

Computational simulation of ionization processes in single-bubble and multi-bubble sonoluminescence

Jin-Fu Liang(梁金福), De-Feng Xiong(熊德凤), Yu An(安宇), and Wei-Zhong Chen(陈伟中)

Chin. Phys. B, 2022, 31 (11): 117802. DOI: 10.1088/1674-1056/ac6745

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The most recent spectroscopic studies of moving-single bubble sonoluminescence (MSBSL) and multi-bubble sonoluminescence (MBSL) have revealed that hydrated electrons (e$_{{\rm aq}}^{-}$) are generated in MSBSL but absent in MBSL. To explore the mechanism of this phenomenon, we numerically simulate the ionization processes in single- and multi-bubble sonoluminescence in aqueous solution of terbium chloride (TbCl$_{3}$). The results show that the maximum degree of ionization of single-bubble sonoluminescence (SBSL) is approximately 10000 times greater than that of MBSL under certain special physical parameters. The hydrated electrons (e$_{{{\rm aq}}}^{-}$) formed in SBSL are far more than those in MBSL provided these electrons are ejected from a bubble into a liquid. Therefore, the quenching of e$_{{{\rm aq}}}^{-}$ to SBSL spectrum is stronger than that of the MBSL spectrum. This may be the reason that the trivalent terbium [Tb(III)] ion line intensities from SBSL in the TbCl$_{3}$ aqueous solutions with the acceptor of e$_{{{\rm aq}}}^{-}$ are stronger than those of TbCl$_{3}$ aqueous solutions without the acceptor of e$_{{{\rm aq}}}^{-}$. Whereas the Tb(III) ion line intensities from MBSL are not variational, which is significant for exploring the mechanism behind the cavitation and sonoluminescence.

Water adsorption performance of UiO-66 modified by MgCl₂ for heat transformation applications

Jia-Li Liu(刘佳丽), Guo-Dong Fu(付国栋), Ping Wu(吴平), Shang Liu(刘尚), Jin-Guang Yang(杨金光), Shi-Ping Zhang(张师平), Li Wang(王立), Min Xu(许闽), and Xiu-Lan Huai(淮秀兰)

Chin. Phys. B, 2022, 31 (11): 118101. DOI: 10.1088/1674-1056/ac7b1f

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UiO-66 is a potential material for adsorption heat transformation (AHT) with high specific surface area, and excellent thermal and chemical stability. However, the low water adsorption capacity of UiO-66 in the low relative pressure range ($0< P/P_0< 0.3$) limits its application in AHT. We prepare the UiO-66 modified by MgCl$_{2 }$ through using the solvothermal method and impregnation method, and study their water vapor adsorption performances and heat storage capacities. Attributed to the extremely high saturated water uptake and excellent hydrophilicity of MgCl$_{2}$, the water adsorption performance of UiO-66 is improved, although the introduction of MgCl$_{2}$ reduces its specific surface area and pore volume. The water adsorption capacity at $P/P_0=0.3$ and the saturated water adsorption capacity of the UiO-66 (with MgCl$_{2}$ content of 0.57 wt%) modified by the solvothermal method are 0.27 g/g and 0.57 g/g at 298 K, respectively, which are 68.8% and 32.6% higher than the counterparts of pure UiO-66, respectively. Comparing with pure UiO-66, the water adsorption capacity of the UiO-66 (with MgCl$_{2}$ content of 1.02 wt%) modified by the impregnation method is increased by 56.3% and 14.0% at the same pressure, respectively. During 20 water adsorption/desorption cycles, the above two materials show high heat storage densities ($\sim1293 $ J/g and 1378 J/g). Therein, the UiO-66 modified by the solvothermal method exhibits the excellent cyclic stability. These results suggest that the introduction of an appropriate amount of MgCl$_{2}$ makes UiO-66 more suitable for AHT applications.

Significant suppression of residual nitrogen incorporation in diamond film with a novel susceptor geometry employed in MPCVD Suggested by editors

Weikang Zhao(赵伟康), Yan Teng(滕妍), Kun Tang(汤琨), Shunming Zhu(朱顺明), Kai Yang(杨凯), Jingjing Duan(段晶晶), Yingmeng Huang(黄颖蒙), Ziang Chen(陈子昂), Jiandong Ye(叶建东), and Shulin Gu(顾书林)

Chin. Phys. B, 2022, 31 (11): 118102. DOI: 10.1088/1674-1056/ac7298

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This work proposed to change the structure of the sample susceptor of the microwave plasma chemical vapor deposition (MPCVD) reaction chamber, that is, to introduce a small hole in the center of the susceptor to study its suppression effect on the incorporation of residual nitrogen in the MPCVD diamond film. By using COMSOL multiphysics software simulation, the plasma characteristics and the concentration of chemical reactants in the cylindrical cavity of MPCVD system were studied, including electric field intensity, electron number density, electron temperature, the concentrations of atomic hydrogen, methyl, and nitrogenous substances, etc. After introducing a small hole in the center of the molybdenum support susceptor, we found that no significant changes were found in the center area of the plasma, but the electron state in the plasma changed greatly on the surface above the susceptor. The electron number density was reduced by about 40%, while the electron temperature was reduced by about 0.02 eV, and the concentration of atomic nitrogen was decreased by about an order of magnitude. Moreover, we found that if a specific lower microwave input power is used, and a susceptor structure without the small hole is introduced, the change results similar to those in the surface area of the susceptor will be obtained, but the spatial distribution of electromagnetic field and reactant concentration will be changed.

Enhanced and tunable circular dichroism in the visible waveband by coupling of the waveguide mode and local surface plasmon resonances in double-layer asymmetric metal grating

Liu-Li Wang(王刘丽), Yang Gu(顾阳), Yi-Jing Chen(陈怡静), Ya-Xian Ni(倪亚贤), and Wen Dong(董雯)

Chin. Phys. B, 2022, 31 (11): 118103. DOI: 10.1088/1674-1056/ac6494

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Circular dichroism (CD) has shown very interesting possibilities as a means to characterize the chiral signal of a chiral structure. Here, we theoretically demonstrated enhanced and tunable CD in the visible light regime using a composite structure consisting of a double-layer metal grating gaped by a dielectric waveguide layer. Based on the coupling of the waveguide modes and the localized plasmonic resonances, the CD could reach a maximum value as high as 0.52 at 635 nm, which is four times higher than the CD value obtained in a conventional double-layer grating without the waveguide coupling effect. Furthermore, the spectral positions of the enhanced CD bands could be easily tuned by controlling the structural parameters. The proposed hybrid double-grating and waveguide structures could have potential applications in chiral selective imaging, sensing and spectroscopy, especially where the transmission measurement is required.

Enrichment of microplastic pollution by micro-nanobubbles

Jing Wang(王菁), Zihan Wang(王子菡), Fangyuan Pei(裴芳源), and Xingya Wang(王兴亚)

Chin. Phys. B, 2022, 31 (11): 118104. DOI: 10.1088/1674-1056/ac6161

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Microplastic pollution has become a global environmental concern. It has been reported that microplastics are easily accessible to a wide range of aquatic organisms and ultimately enter the human body along the food chain. They pose a severe threat to ecosystems, organisms and even human health due to their durability and persistence. However, how to reduce microplastic pollution still remains a challenge in terms of scientific techniques and policy-making. There is currently still a lack of effective methods for microplastic recycling and removal. Luckily, a new technique, micro-nanobubbles (MNBs), may provide a possible and highly effective method to enrich microplastic pollution: their great advantages^[1] include a high specific surface area, long lifetime and ability to adsorb microplastics of the same size and hydrophobicity. Then they further adsorb on larger bubbles such as microbubbles or millimeter bubbles and float to the water surface together. In this study, we present a new method using MNBs to enrich microplastic pollution with high efficiency. Two types of microplastics, millimeter-scale plastic fragments and microplastic particles, were chosen as the model microplastic pollution systems to study the enrichment efficiency of MNBs on microplastics. Results showed that MNBs can efficiently enrich these microplastics. The enrichment efficiency increases with flotation time until a maximum value is reached. It is proved that MNBs not only collect the microplastic pollution but also reduce detergent use in domestic laundry sewage. This is because detergent, as a surfactant, is easily absorbed on the surface of MNBs and can be collected together with the microplastic pollution. Our research has demonstrated that the MNB technique could be promising for use in microplastic recycling and reducing detergent pollution in daily life.

Accelerated oxygen evolution kinetics on Ir-doped SrTiO₃ perovskite by NH₃ plasma treatment

Li-Li Deng(邓丽丽), Xiao-Ping Ma(马晓萍), Man-Ting Lu(卢曼婷), Yi He(何弈), Rong-Lei Fan(范荣磊), and Yu Xin(辛煜)

Chin. Phys. B, 2022, 31 (11): 118201. DOI: 10.1088/1674-1056/ac70b1

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Exploring low-cost and high-performance catalysts for oxygen evolution reaction (OER) remains to be a great challenge. Iridium-based perovskite oxide has large potential in OER because of its intrinsic activity and outstanding physicochemical properties. In this study, iridium-doped strontium titanate (Ir-STO) solution is brushed on a Ti sheet by the traditional method to obtain the Ir-STO/Ti electrodes after being calcined at a high temperature. The microstructure and electrocatalysis properties of the Ir-STO are further modified by a facile and scalable NH₃-plasma strategy. In addition to the doping of Ir, the NH₃ plasma treatment further results in N-doping into Ir-STO, which enriches active species and causes oxygen vacancies near doped sites. The resulting N, Ir-STO/Ti electrode reveals excellent acidic OER activity with the lowest overpotential of 390 mV at 10 mA/cm² and the smallest Tafel slope of 140 mV/dec after 10-min plasma treatment. Therefore, the great potential of activated N, Ir-STO/Ti is regarded as a catalyst for the OER, and thus making a new opportunity for developing other perovskite catalysts via NH₃ plasma treatment.

Designing current-strain-assisted superconductor-ferromagnet multi-bit memories

Hasnain Mehdi Jafri, Jing Wang(王静), Xiao-Ming Shi(施小明), De-Shan Liang(梁德山), and Hou-Bing Huang(黄厚兵)

Chin. Phys. B, 2022, 31 (11): 118501. DOI: 10.1088/1674-1056/ac7e36

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Current superconducting memory devices lack the basic quality of high memory density for practical memories, mainly due to the size limitations of superconducting quantum interference devices. Here, we propose a superconductor-ferromagnet bilayer device with strain-pulse-assisted multi-bit ladder-type memory, by using strain-engineered ferromagnet domain structure to control carrier concentration in the superconductor, which is simulated by coupled Landau-Lifshitz-Gilbert and Ginzburg-Landau equations. Current- and strain-pulses are observed to deterministically control the resistivity of superconductor for one and two-bit device arrangements. The average carrier concentration of superconductor is observed to have multiple metastable states that can be controllably switched using current-pulse and strain-pulse to determine multiple resistivity states. These findings confirm the eligibility of superconductor-ferromagnet bilayers to be used as ladder-type multibit memories and open a new way for further theoretical and experimental investigations of the cryogenic memories.

Pattern transition and regulation in a subthalamopallidal network under electromagnetic effect

Zilu Cao(曹子露), Lin Du(都琳), Honghui Zhang(张红慧), Yuzhi Zhao(赵玉枝), Zhuan Shen(申转), and Zichen Deng(邓子辰)

Chin. Phys. B, 2022, 31 (11): 118701. DOI: 10.1088/1674-1056/ac80ae

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Although the significant roles of magnetic induction and electromagnetic radiation in the neural system have been widely studied, their influence on Parkinson's disease (PD) has yet to be well explored. By virtue of the magnetic flux variable, this paper studies the transition of firing patterns induced by magnetic induction and the regulation effect of external magnetic radiation on the firing activities of the subthalamopallidal network in basal ganglia. We find: (i) The network reproduces five typical waveforms corresponding to the severity of symptoms: weak cluster, episodic, continuous cluster, episodic, and continuous wave. (ii) Magnetic induction is a double-edged sword for the treatment of PD. Although the increase of magnetic coefficient may lead the physiological firing activity to transfer to pathological firing activity, it also can regulate the pathological intensity firing activity with excessive β-band power transferring to the physiological firing pattern with weak β-band power. (iii) External magnetic radiation could inhibit continuous tremulous firing and β-band power of subthalamic nucleus (STN), which means the severity of symptoms weakened. Especially, the bi-parameter plane of the regulation region shows that a short pulse period of magnetic radiation and a medium level of pulse percentage can well regulate pathological oscillation. This work helps to understand the firing activity of the subthalamopallidal network under electromagnetic effect. It may also provide insights into the mechanisms behind the electromagnetic therapy of PD-related firing activity.

Biased random walk with restart for essential proteins prediction Suggested by editors

Pengli Lu(卢鹏丽), Yuntian Chen(陈云天), Teng Zhang(张腾), and Yonggang Liao(廖永刚)

Chin. Phys. B, 2022, 31 (11): 118901. DOI: 10.1088/1674-1056/ac7a17

Abstract ( 276 )

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Predicting essential proteins is crucial for discovering the process of cellular organization and viability. We propose biased random walk with restart algorithm for essential proteins prediction, called BRWR. Firstly, the common process of practice walk often sets the probability of particles transferring to adjacent nodes to be equal, neglecting the influence of the similarity structure on the transition probability. To address this problem, we redefine a novel transition probability matrix by integrating the gene express similarity and subcellular location similarity. The particles can obtain biased transferring probabilities to perform random walk so as to further exploit biological properties embedded in the network structure. Secondly, we use gene ontology (GO) terms score and subcellular score to calculate the initial probability vector of the random walk with restart. Finally, when the biased random walk with restart process reaches steady state, the protein importance score is obtained. In order to demonstrate superiority of BRWR, we conduct experiments on the YHQ, BioGRID, Krogan and Gavin PPI networks. The results show that the method BRWR is superior to other state-of-the-art methods in essential proteins recognition performance. Especially, compared with the contrast methods, the improvements of BRWR in terms of the ACC results range in 1.4%-5.7%, 1.3%-11.9%, 2.4%-8.8%, and 0.8%-14.2%, respectively. Therefore, BRWR is effective and reasonable.

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