Chin. Phys. B

Anomalous valley Hall effect in two-dimensional valleytronic materials

Hongxin Chen(陈洪欣), Xiaobo Yuan(原晓波), and Junfeng Ren(任俊峰)

Chin. Phys. B, 2024, 33 (4): 047304. DOI: 10.1088/1674-1056/ad1c59

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The anomalous valley Hall effect (AVHE) can be used to explore and utilize valley degrees of freedom in materials, which has potential applications in fields such as information storage, quantum computing and optoelectronics. AVHE exists in two-dimensional (2D) materials possessing valley polarization (VP), and such 2D materials usually belong to the hexagonal honeycomb lattice. Therefore, it is necessary to achieve valleytronic materials with VP that are more readily to be synthesized and applicated experimentally. In this topical review, we introduce recent developments on realizing VP as well as AVHE through different methods, i.e., doping transition metal atoms, building ferrovalley heterostructures and searching for ferrovalley materials. Moreover, 2D ferrovalley systems under external modulation are also discussed. 2D valleytronic materials with AVHE demonstrate excellent performance and potential applications, which offer the possibility of realizing novel low-energy-consuming devices, facilitating further development of device technology, realizing miniaturization and enhancing functionality of them.

Transport properties of Hall-type quantum states in disordered bismuthene

Jiaojiao Zhou(周娇娇), Jiangying Yu(余江应), Shuguang Cheng(成淑光), and Hua Jiang(江华)

Chin. Phys. B, 2024, 33 (4): 047105. DOI: 10.1088/1674-1056/ad2605

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Bismuthene, an inherently hexagonal structure characterized by a huge bulk gap, offers a versatile platform for investigating the electronic transport of various topological quantum states. Using nonequilibrium Green's function method and Landauer—Büttiker formula, we thoroughly investigate the transport properties of various Hall-type quantum states, including quantum spin Hall (QSH) edge states, quantum valley Hall kink (QVHK) states, and quantum spin—valley Hall kink (QSVHK) states, in the presence of various disorders. Based on the exotic transport features, a spin—valley filter, capable of generating a highly spin- and valley-polarized current, is proposed. The valley index and the spin index of the filtered QSVHK state are determined by the staggered potential and the intrinsic spin—orbit coupling, respectively. The efficiency of the spin—valley filter is supported by the spacial current distribution, the valley-resolved conductance, and the spin-resolved conductance. Compared with a sandwich structure for QSVHK, our proposed spin—valley filter can work with a much smaller size and is more accessible in the experiment.

Strong field ionization of molecules on the surface of nanosystems

Qiwen Qu(曲棋文), Fenghao Sun(孙烽豪), Jiawei Wang(王佳伟), Jian Gao(高健), Hui Li(李辉), and Jian Wu(吴健)

Chin. Phys. B, 2024, 33 (4): 047803. DOI: 10.1088/1674-1056/ad2509

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Besides the diverse investigations on the interactions between intense laser fields and molecular systems, extensive research has been recently dedicated to exploring the response of nanosystems excited by well-tailored femtosecond laser fields. Due to the fact that nanostructures hold peculiar effects when illuminated by laser pulses, the underlying mechanisms and the corresponding potential applications can make significant improvements in both fundamental research and development of novel techniques. In this review, we provide a summarization of the strong field ionization occurring on the surface of nanosystems. The molecules attached to the nanoparticle surface perform as the precursor in the ionization and excitation of the whole nanosystem, the fundamental processes of which are yet to be discovered. We discuss the influence on nanoparticle constituents, geometric shapes and sizes, as well as the specific waveforms of the excitation laser fields. The intriguing characteristics observed in surface ion emission reflect how enhanced near field affects the localized ionizations and nanoplasma expansions, thereby paving the way for further precision controls on the light-and-matter interactions in the extreme spatial temporal levels.

Plasmon-induced nonlinear response on gold nanoclusters

Yuhui Song(宋玉慧), Yifei Cao(曹逸飞), Sichen Huang(黄思晨), Kaichao Li(李凯超), Ruhai Du(杜如海), Lei Yan(严蕾), Zhengkun Fu(付正坤), and Zhenglong Zhang(张正龙)

Chin. Phys. B, 2024, 33 (4): 044204. DOI: 10.1088/1674-1056/ad1a8b

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The plasmon-induced nonlinear response has attracted great attention in micro-nano optics and optoelectronics applications, yet the underlying microscopic mechanism remains elusive. In this study, the nonlinear response of gold nanoclusters when exposed to a femtosecond laser pulse was investigated using time-dependent density functional theory. It was observed that the third-order tunneling current was augmented in plasmonic dimers, owing to a greater number of electrons in the dimer being excited from occupied to unoccupied states. These findings provide profound theoretical insights and enable the realization of accurate regulation and control of nonlinear effects induced by plasmons at the atomic level.

General three-dimensional thermal illusion metamaterials

Tianfeng Liu(刘天丰), Zhaochen Wang(王兆宸), Zhan Zhu(朱展), and Run Hu(胡润)

Chin. Phys. B, 2024, 33 (4): 044401. DOI: 10.1088/1674-1056/ad09aa

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Thermal illusion aims to create fake thermal signals or hide the thermal target from the background thermal field to mislead infrared observers, and illusion thermotics was proposed to regulate heat flux with artificially structured metamaterials for thermal illusion. Most theoretical and experimental works on illusion thermotics focus on two-dimensional materials, while heat transfer in real three-dimensional (3D) objects remains elusive, so the general 3D illusion thermotics is urgently demanded. In this study, we propose a general method to design 3D thermal illusion metamaterials with varying illusions at different sizes and positions. To validate the generality of the 3D method for thermal illusion metamaterials, we realize thermal functionalities of thermal shifting, splitting, trapping, amplifying and compressing. In addition, we propose a special way to simplify the design method under the condition that the size of illusion target is equal to the size of original heat source. The 3D thermal illusion metamaterial paves a general way for illusion thermotics and triggers the exploration of illusion metamaterials for more functionalities and applications.

Thermal transport in composition graded silicene/germanene heterostructures

Zengqiang Cao(曹增强), Chaoyu Wang(王超宇), Honggang Zhang(张宏岗), Bo You(游波), and Yuxiang Ni(倪宇翔)

Chin. Phys. B, 2024, 33 (4): 044402. DOI: 10.1088/1674-1056/ad1500

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Through equilibrium and non-equilibrium molecular dynamics simulations, we have demonstrated the inhibitory effect of composition graded interface on thermal transport behavior in lateral heterostructures. Specifically, we investigated the influence of composition gradient length and heterogeneous particles at the silicene/germanene (SIL/GER) heterostructure interface on heat conduction. Our results indicate that composition graded interface at the interface diminishes the thermal conductivity of the heterostructure, with a further reduction observed as the length increases, while the effect of the heterogeneous particles can be considered negligible. To unveil the influence of composition graded interface on thermal transport, we conducted phonon analysis and identified the presence of phonon localization within the interface composition graded region. Through these analyses, we have determined that the decrease in thermal conductivity is correlated with phonon localization within the heterostructure, where a stronger degree of phonon localization signifies poorer thermal conductivity in the material. Our research findings not only contribute to understanding the impact of interface gradient-induced phonon localization on thermal transport but also offer insights into the modulation of thermal conductivity in heterostructures.

Influence of substrate effect on near-field radiative modulator based on biaxial hyperbolic materials

Ruiyi Liu(刘睿一), Haotuo Liu(刘皓佗), Yang Hu(胡杨), Zheng Cui(崔峥), and Xiaohu Wu(吴小虎)

Chin. Phys. B, 2024, 33 (4): 044403. DOI: 10.1088/1674-1056/ad2a6c

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Relative rotation between the emitter and receiver could effectively modulate the near-field radiative heat transfer (NFRHT) in anisotropic media. Due to the strong in-plane anisotropy, natural hyperbolic materials can be used to construct near-field radiative modulators with excellent modulation effects. However, in practical applications, natural hyperbolic materials need to be deposited on the substrate, and the influence of substrate on modulation effect has not been studied yet. In this work, we investigate the influence of substrate effect on near-field radiative modulator based on α-MoO₃. The results show that compared to the situation without a substrate, the presence of both lossless and lossy substrate will reduce the modulation contrast (MC) for different film thicknesses. When the real or imaginary component of the substrate permittivity increases, the mismatch of hyperbolic phonon polaritons (HPPs) weakens, resulting in a reduction in MC. By reducing the real and imaginary components of substrate permittivity, the MC can be significantly improved, reaching 4.64 for ε_s = 3 at t = 10 nm. This work indicates that choosing a substrate with a smaller permittivity helps to achieve a better modulation effect, and provides guidance for the application of natural hyperbolic materials in the near-field radiative modulator.

Controlled thermally-driven mass transport in carbon nanotubes using carbon hoops

Yaolong Li(李耀隆), Songyuan Li(李松远), Meifen Wang(王美芬), and Renliang Zhang(张任良)

Chin. Phys. B, 2024, 33 (4): 046101. DOI: 10.1088/1674-1056/ad14ff

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Controlling mass transportation using intrinsic mechanisms is a challenging topic in nanotechnology. Herein, we employ molecular dynamics simulations to investigate the mass transport inside carbon nanotubes (CNT) with temperature gradients, specifically the effects of adding a static carbon hoop to the outside of a CNT on the transport of a nanomotor inside the CNT. We reveal that the underlying mechanism is the uneven potential energy created by the hoops, i.e., the hoop outside the CNT forms potential energy barriers or wells that affect mass transport inside the CNT. This fundamental control of directional mass transportation may lead to promising routes for nanoscale actuation and energy conversion.

Phonon transport properties of Janus Pb₂XAs(X = P, Sb, and Bi) monolayers: A DFT study

Jiaxin Geng(耿嘉鑫), Pei Zhang(张培), Zhunyun Tang(汤准韵), and Tao Ouyang(欧阳滔)

Chin. Phys. B, 2024, 33 (4): 046501. DOI: 10.1088/1674-1056/ad2260

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Grasping the underlying mechanisms behind the low lattice thermal conductivity of materials is essential for the efficient design and development of high-performance thermoelectric materials and thermal barrier coating materials. In this paper, we present a first-principles calculations of the phonon transport properties of Janus Pb₂PAs and Pb₂SbAs monolayers. Both materials possess low lattice thermal conductivity, at least two orders of magnitude lower than graphene and h-BN. The room temperature thermal conductivity of Pb₂SbAs (0.91 W/mK) is only a quarter of that of Pb₂PAs (3.88 W/mK). We analyze in depth the bonding, lattice dynamics, and phonon mode level information of these materials. Ultimately, it is determined that the synergistic effect of low group velocity due to weak bonding and strong phonon anharmonicity is the fundamental cause of the intrinsic low thermal conductivity in these Janus structures. Relative regular residual analysis further indicates that the four-phonon processes are limited in Pb₂PAs and Pb₂SbAs, and the three-phonon scattering is sufficient to describe their anharmonicity. In this study, the thermal transport properties of Janus Pb₂PAs and Pb₂SbAs monolayers are illuminated based on fundamental physical mechanisms, and the low lattice thermal conductivity endows them with the potential applications in the field of thermal barriers and thermoelectrics.

Wide frequency phonons manipulation in Si nanowire by introducing nanopillars and nanoparticles

Yatao Li(李亚涛), Yingguang Liu(刘英光), Xin Li(李鑫), Hengxuan Li(李亨宣), Zhixiang Wang(王志香), and Jiuyi Zhang(张久意)

Chin. Phys. B, 2024, 33 (4): 046502. DOI: 10.1088/1674-1056/ad0290

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The combination of different nanostructures can hinder phonons transmission in a wide frequency range and further reduce the thermal conductivity (TC). This will benefit the improvement and application of thermoelectric conversion, insulating materials and thermal barrier coatings, etc. In this work, the effects of nanopillars and Ge nanoparticles (GNPs) on the thermal transport of Si nanowire (SN) are investigated by nonequilibrium molecular dynamics (NEMD) simulation. By analyzing phonons transport behaviors, it is confirmed that the introduction of nanopillars leads to the occurrence of low-frequency phonons resonance, and nanoparticles enhance high-frequency phonons interface scattering and localization. The results show that phonons transport in the whole frequency range can be strongly hindered by the simultaneous introduction of nanopillars and nanoparticles. In addition, the effects of system length, temperature, sizes and numbers of nanoparticles on the TC are investigated. Our work provides useful insights into the effective regulation of the TC of nanomaterials.

Diameter-dependent ultra-high thermoelectric performance of ZnO nanowires

Yinan Nie(聂祎楠), Guihua Tang(唐桂华), Yifei Li(李一斐), Min Zhang(张敏), and Xin Zhao(赵欣)

Chin. Phys. B, 2024, 33 (4): 047301. DOI: 10.1088/1674-1056/ad11e5

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Zinc oxide (ZnO) shows great potential in electronics, but its large intrinsic thermal conductivity limits its thermoelectric applications. In this work, we explore the significant carrier transport capacity and diameter-dependent thermoelectric characteristics of wurtzite-ZnO<0001> nanowires based on first-principles and molecular dynamics simulations. Under the synergistic effect of band degeneracy and weak phonon—electron scattering, P-type (ZnO)₇₃ nanowires achieve an ultra-high power factor above 1500 μW· cm^-1· K^-2 over a wide temperature range. The lattice thermal conductivity and carrier transport properties of ZnO nanowires exhibit a strong diameter size dependence. When the ZnO nanowire diameter exceeds 12.72 Å, the carrier transport properties increase significantly, while the thermal conductivity shows a slight increase with the diameter size, resulting in a ZT value of up to 6.4 at 700 K for P-type (ZnO)₇₃. For the first time, the size effect is also illustrated by introducing two geometrical configurations of the ZnO nanowires. This work theoretically depicts the size optimization strategy for the thermoelectric conversion of ZnO nanowires.

Phonon resonance modulation in weak van der Waals heterostructures: Controlling thermal transport in graphene—silicon nanoparticle systems

Yi Li(李毅), Yinong Liu(刘一浓), and Shiqian Hu(胡世谦)

Chin. Phys. B, 2024, 33 (4): 047401. DOI: 10.1088/1674-1056/ad1501

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The drive for efficient thermal management has intensified with the miniaturization of electronic devices. This study explores the modulation of phonon transport within graphene by introducing silicon nanoparticles influenced by van der Waals forces. Our approach involves the application of non-equilibrium molecular dynamics to assess thermal conductivity while varying the interaction strength, leading to a noteworthy reduction in thermal conductivity. Furthermore, we observe a distinct attenuation in length-dependent behavior within the graphene—nanoparticles system. Our exploration combines wave packet simulations with phonon transmission calculations, aligning with a comprehensive analysis of the phonon transport regime to unveil the underlying physical mechanisms at play. Lastly, we conduct transient molecular dynamics simulations to investigate interfacial thermal conductance between the nanoparticles and the graphene, revealing an enhanced thermal boundary conductance. This research not only contributes to our understanding of phonon transport but also opens a new degree of freedom for utilizing van der Waals nanoparticle-induced resonance, offering promising avenues for the modulation of thermal properties in advanced materials and enhancing their performance in various technological applications.

Thermal conductivity of GeTe crystals based on machine learning potentials

Jian Zhang(张健), Hao-Chun Zhang(张昊春), Weifeng Li(李伟峰), and Gang Zhang(张刚)

Chin. Phys. B, 2024, 33 (4): 047402. DOI: 10.1088/1674-1056/ad1b42

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GeTe has attracted extensive research interest for thermoelectric applications. In this paper, we first train a neuro-evolution potential (NEP) based on a dataset constructed by ab initio molecular dynamics, with the Gaussian approximation potential (GAP) as a reference. The phonon density of states is then calculated by two machine learning potentials and compared with density functional theory results, with the GAP potential having higher accuracy. Next, the thermal conductivity of a GeTe crystal at 300 K is calculated by the equilibrium molecular dynamics method using both machine learning potentials, and both of them are in good agreement with the experimental results; however, the calculation speed when using the NEP potential is about 500 times faster than when using the GAP potential. Finally, the lattice thermal conductivity in the range of 300 K—600 K is calculated using the NEP potential. The lattice thermal conductivity decreases as the temperature increases due to the phonon anharmonic effect. This study provides a theoretical tool for the study of the thermal conductivity of GeTe.

Near-field radiative heat transfer between nanoporous GaN films

Xiaozheng Han(韩晓政), Jihong Zhang(张纪红), Haotuo Liu(刘皓佗), Xiaohu Wu(吴小虎), and Huiwen Leng(冷惠文)

Chin. Phys. B, 2024, 33 (4): 047801. DOI: 10.1088/1674-1056/ad09a9

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Photon tunneling effects give rise to surface waves, amplifying radiative heat transfer in the near-field regime. Recent research has highlighted that the introduction of nanopores into materials creates additional pathways for heat transfer, leading to a substantial enhancement of near-field radiative heat transfer (NFRHT). Being a direct bandgap semiconductor, GaN has high thermal conductivity and stable resistance at high temperatures, and holds significant potential for applications in optoelectronic devices. Indeed, study of NFRHT between nanoporous GaN films is currently lacking, hence the physical mechanism for adding nanopores to GaN films remains to be discussed in the field of NFRHT. In this work, we delve into the NFRHT of GaN nanoporous films in terms of gap distance, GaN film thickness and the vacuum filling ratio. The results demonstrate a 27.2% increase in heat flux for a 10 nm gap when the nanoporous filling ratio is 0.5. Moreover, the spectral heat flux exhibits redshift with increase in the vacuum filling ratio. To be more precise, the peak of spectral heat flux moves from ω = 1.31×10¹⁴ rad·s^-1 to ω = 1.23×10¹⁴ rad·s^-1 when the vacuum filling ratio changes from f = 0.1 to f = 0.5; this can be attributed to the excitation of surface phonon polaritons. The introduction of graphene into these configurations can highly enhance the NFRHT, and the spectral heat flux exhibits a blueshift with increase in the vacuum filling ratio, which can be explained by the excitation of surface plasmon polaritons. These findings offer theoretical insights that can guide the extensive utilization of porous structures in thermal control, management and thermal modulation.

Building and characterizing a stylus ion-trap system

Tai-Hao Cui(崔太豪), Ya-Qi Wei(魏雅琪), Ji Li(李冀), Quan Yuan(袁泉), Shuang-Qing Dai(戴双晴), Pei-Dong Li(李沛东), Fei Zhou(周飞), Jian-Qi Zhang(张建奇), Zhu-Jun Zheng(郑驻军), Liang Chen(陈亮), and Mang Feng(冯芒)

Chin. Phys. B, 2024, 33 (4): 043701. DOI: 10.1088/1674-1056/ad22d9

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Cold trapped ions can be excellent sensors for ultra-precision detection of physical quantities, which strongly depends on the measurement situation at hand. The stylus ion trap, formed by two concentric cylinders over a ground plane, holds the promise of relatively simple structure and larger solid angle for optical access and fluorescence collection in comparison with the conventional ion traps. Here we report our fabrication and characterization of the first stylus ion trap constructed in China, aiming for studying quantum optics and sensing weak electric fields in the future. We have observed the stable confinement of the ion in the trapping potential for more than two hours and measured the heating rate of the trap to be dε/dt=7.10±0.13 meV/s by the Doppler recooling method. Our work starts a way to building practical quantum sensors with high efficiency of optical collection and with ultimate goal for contributing to future quantum information technology.

Probing the peripheral self-generated magnetic field distribution in laser-plasma magnetic reconnection with Martin—Puplett interferometer polarimeter

Ya-Peng Zhang(张雅芃), Jia-Wen Yao(姚嘉文), Zheng-Dong Liu(刘正东), Zuo-Lin Ma(马作霖), and Jia-Yong Zhong(仲佳勇)

Chin. Phys. B, 2024, 33 (4): 045206. DOI: 10.1088/1674-1056/ad24db

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Magnetic reconnection of the self-generated magnetic fields in laser-plasma interaction is an important laboratory method for modeling high-energy density astronomical and astrophysical phenomena. We use the Martin—Puplett interferometer (MPI) polarimeter to probe the peripheral magnetic fields generated in the common magnetic reconnection configuration, two separated coplanar plane targets, in laser-target interaction. We introduce a new method that can obtain polarization information from the interference pattern instead of the sinusoidal function fitting of the intensity. A bidirectional magnetic field is observed from the side view, which is consistent with the magneto-hydro-dynamical (MHD) simulation results of self-generated magnetic field reconnection. We find that the cancellation of reverse magnetic fields after averaging and integration along the observing direction could reduce the magnetic field strength by one to two orders of magnitude. It indicates that imaging resolution can significantly affect the accuracy of measured magnetic field strength.

Polarization control of above-threshold ionization spectrum in elliptically polarized two-color laser fields Suggested by editors

Fa-Cheng Jin(金发成), Hui-Hui Yang(杨慧慧), Xiao-Hong Song(宋晓红), Fei Li(李飞), Ling-Ling Du(杜玲玲), Hong-Jie Xue(薛红杰), Li-Min Wei(魏丽敏), Yue Bai(白悦), Hao-Xiang Liu(刘浩翔), Bing-Bing Wang(王兵兵), and Wei-Feng Yang(杨玮枫)

Chin. Phys. B, 2024, 33 (4): 043301. DOI: 10.1088/1674-1056/ad24d8

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We study the above-threshold ionization (ATI) process of atoms exposed to fundamental and high-frequency lasers with arbitrary ellipticity by applying the frequency-domain theory. It is found that the angular-resolved ATI spectrum is sensitive to ellipticities of two lasers and emitted angles of the photoelectron. Particularly for the photon energy of the high-frequency laser more than atomic ionization potential, the width of plateau tends to a constant with increasing ellipticity of fundamental field, the dip structure disappears with increasing ellipticity of the high-frequency field. With the help of the quantum channel analysis, it is shown that the angular distribution depends mainly on the ellipticity of high-frequency field in the case that its frequency is high. Moreover, one can see that the maximal and minimal energies in quantum numerical results are in good agreement with the classical prediction. Our investigation may provide theoretical support for experimental research on polarization control of ionization in elliptically polarized two-color laser fields.

Coexistence of Dirac and Weyl points in non-centrosymmetric semimetal NbIrTe₄ ^Hot!

Qingxin Liu(刘清馨), Yang Fu(付阳), Pengfei Ding(丁鹏飞), Huan Ma(马欢), Pengjie Guo(郭朋杰), Hechang Lei(雷和畅), and Shancai Wang(王善才)

Chin. Phys. B, 2024, 33 (4): 047104. DOI: 10.1088/1674-1056/ad2a79

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Using angle-resolved photoemission spectroscopy and density functional theory calculations methods, we investigate the electronic structures and topological properties of ternary tellurides NbIrTe₄, a candidate for type-II Weyl semimetal. We demonstrate the presence of several Fermi arcs connecting their corresponding Weyl points on both termination surfaces of the topological material. Our analysis reveals the existence of Dirac points, in addition to Weyl points, giving both theoretical and experimental evidences of the coexistence of Dirac and Weyl points in a single material. These findings not only confirm NbIrTe₄ as a unique topological semimetal but also open avenues for exploring novel electronic devices based on its coexisting Dirac and Weyl fermions.

Improving the electrical performances of InSe transistors by interface engineering ^Hot!

Tianjun Cao(曹天俊), Song Hao(郝松), Chenchen Wu(吴晨晨), Chen Pan(潘晨), Yudi Dai(戴玉頔), Bin Cheng(程斌), Shi-Jun Liang(梁世军), and Feng Miao(缪峰)

Chin. Phys. B, 2024, 33 (4): 047302. DOI: 10.1088/1674-1056/ad24d7

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InSe has emerged as a promising candidate for next-generation electronics due to its predicted ultrahigh electrical performance. However, the efficacy of the InSe transistor in meeting application requirements is hindered due to its sensitivity to interfaces. In this study, we have achieved notable enhancement in the electrical performance of InSe transistors through interface engineering. We engineered an InSe/h-BN heterostructure, effectively suppressing dielectric layer-induced scattering. Additionally, we successfully established excellent metal—semiconductor contacts using graphene ribbons as a buffer layer. Through a methodical approach to interface engineering, our graphene/InSe/h-BN transistor demonstrates impressive on-state current, field-effect mobility, and on/off ratio at room temperature, reaching values as high as 1.1 mA/μm, 904 cm²·V^-1·s^-1, and >10⁶, respectively. Theoretical computations corroborate that the graphene/InSe heterostructure shows significant interlayer charge transfer and weak interlayer interaction, contributing to the enhanced performance of InSe transistors. This research offers a comprehensive strategy to elevate the electrical performance of InSe transistors, paving the way for their utilization in future electronic applications.

Symmetry transformation of nonlinear optical current of tilted Weyl nodes and application to ferromagnetic MnBi₂Te₄ ^Hot!

Zhuo-Cheng Lu(卢倬成) and Ji Feng(冯济)

Chin. Phys. B, 2024, 33 (4): 047303. DOI: 10.1088/1674-1056/ad2bfb

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A Weyl node is characterized by its chirality and tilt. We develop a theory of how nth-order nonlinear optical conductivity behaves under transformations of anisotropic tensor and tilt, which clarifies how chirality-dependent and -independent parts of optical conductivity transform under the reversal of tilt and chirality. Built on this theory, we propose ferromagnetic m MnBi₂Te₄ as a magnetoelectrically regulated, terahertz optical device, by magnetoelectrically switching the chirality-dependent and -independent DC photocurrents. These results are useful for creating nonlinear optical devices based on the topological Weyl semimetals.

Structure and superconducting properties of Ru_1-xMo_x (x = 0.1—0.9) alloys Suggested by editors

Yang Fu(付阳), Chunsheng Gong(龚春生), Zhijun Tu(涂志俊), Shangjie Tian(田尚杰), Shouguo Wang(王守国), and Hechang Lei(雷和畅)

Chin. Phys. B, 2024, 33 (4): 047404. DOI: 10.1088/1674-1056/ad2a73

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We report the detailed crystal structures and physical properties of Ru_1-xMo_x alloys in the solid solution range of x= 0.1—0.9. Structure characterizations indicate that the crystal structure changes from the hcp-Mg-type, to β-CrFe-type, and then bcc-W-type. The measurements of physical properties show that the Ru_1-xMo_x samples with x≥ 0.2 are superconductors and the superconducting transition temperature T_c as a function of Mo content exhibits a dome-like behavior.

Co-doped BaFe₂As₂ Josephson junction fabricated with a focused helium ion beam ^Hot!

Ziwen Chen(陈紫雯), Yan Zhang(张焱), Ping Ma(马平), Zhongtang Xu(徐中堂), Yulong Li(李宇龙), Yue Wang(王越), Jianming Lu(路建明), Yanwei Ma(马衍伟), and Zizhao Gan(甘子钊)

Chin. Phys. B, 2024, 33 (4): 047405. DOI: 10.1088/1674-1056/ad21f7

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Josephson junction plays a key role not only in studying the basic physics of unconventional iron-based superconductors but also in realizing practical application of thin-film based devices, therefore the preparation of high-quality iron pnictide Josephson junctions is of great importance. In this work, we have successfully fabricated Josephson junctions from Co-doped BaFe₂As₂ thin films using a direct junction fabrication technique which utilizes high energy focused helium ion beam (FHIB). The electrical transport properties were investigated for junctions fabricated with various He⁺ irradiation doses. The junctions show sharp superconducting transition around 24 K with a narrow transition width of 2.5 K, and a dose correlated foot-structure resistance which corresponds to the effective tuning of junction properties by He⁺ irradiation. Significant J_c suppression by more than two orders of magnitude can be achieved by increasing the He⁺ irradiation dose, which is advantageous for the realization of low noise ion pnictide thin film devices. Clear Shapiro steps are observed under 10 GHz microwave irradiation. The above results demonstrate the successful fabrication of high quality and controllable Co-doped BaFe₂As₂ Josephson junction with high reproducibility using the FHIB technique, laying the foundation for future investigating the mechanism of iron-based superconductors, and also the further implementation in various superconducting electronic devices.

Robust T_c in element molybdenum up to 160 GPa Suggested by editors

Xinyue Wu(吴新月), Shumin Guo(郭淑敏), Jianning Guo(郭鉴宁), Su Chen(陈诉), Yulong Wang(王煜龙), Kexin Zhang(张可欣), Chengcheng Zhu(朱程程), Chenchen Liu(刘晨晨), Xiaoli Huang(黄晓丽), Defang Duan(段德芳), and Tian Cui(崔田)

Chin. Phys. B, 2024, 33 (4): 047406. DOI: 10.1088/1674-1056/ad2a78

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Element superconductors with the single atoms provide clean and fundamental platforms for studying superconductivity. Although elements with d electrons are usually not favored by conventional BCS, the record superconducting critical temperature (T_c) in element scandium (Sc) has further ignited the intensive attention on transition metals. The element molybdenum (Mo) with a half-full d-orbital is studied in our work, which fills the gap in the study of Mo under high pressure and investigates the pressure dependence of superconductivity. In this work, we exhibit a robust superconductivity of Mo in the pressure range of 5 GPa to 160 GPa via high-pressure electrical transport measurements, the T_c varies at a rate of 0.013 K/GPa to 8.56 K at 160 GPa. Moreover, the superconductivity is evidenced by the T_c shifting to lower temperature under applied magnetic fields, and the upper critical magnetic fields are extrapolated by the WHH equation and GL equation; the results indicate that the maximum upper critical magnetic field is estimated to be 8.24 T at 137 GPa. We further investigate the superconducting mechanism of Mo, the theoretical calculations indicate that the superconductivity can be attributed to the strong coupling between the electrons from the partially filled d band and the phonons from the frequency zone of 200—400 cm^-1.

Localization effect in single crystal of RuAs₂ ^Hot!

Zhe-Kai Yi(易哲铠), Qi Liu(刘琪), Shuang-Kui Guang(光双魁), Sheng Xu(徐升), Xiao-Yu Yue(岳小宇), Hui Liang(梁慧), Na Li(李娜), Ying Zhou(周颖), Dan-Dan Wu(吴丹丹), Yan Sun(孙燕), Qiu-Ju Li(李秋菊), Peng Cheng(程鹏), Tian-Long Xia(夏天龙), Xue-Feng Sun(孙学峰), and Yi-Yan Wang(王义炎)

Chin. Phys. B, 2024, 33 (4): 047501. DOI: 10.1088/1674-1056/ad23d9

Abstract ( 212 )

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We report the magnetotransport and thermal properties of RuAs₂ single crystal. RuAs₂ exhibits semiconductor behavior and localization effect. The crossover from normal state to diffusive transport in the weak localization (WL) state and then to variable range hopping (VRH) transport in the strong localization state has been observed. The transitions can be reflected in the measurement of resistivity and Seebeck coefficient. Negative magnetoresistance (NMR) emerges with the appearance of localization effect and is gradually suppressed in high magnetic field. The temperature dependent phase coherence length extracted from the fittings of NMR also indicates the transition from WL to VRH. The measurement of Hall effect reveals an anomaly of temperature dependent carrier concentration caused by localization effect. Our findings show that RuAs₂ is a suitable platform to study the localized state.

BaTiO₃/p-GaN/Au self-driven UV photodetector with bipolar photocurrent controlled by ferroelectric polarization Suggested by editors

Wushuang Han(韩无双), Kewei Liu(刘可为), Jialin Yang(杨佳霖), Yongxue Zhu(朱勇学), Zhen Cheng(程祯), Xing Chen(陈星), Binghui Li(李炳辉), Lei Liu(刘雷), and Dezhen Shen(申德振)

Chin. Phys. B, 2024, 33 (4): 047701. DOI: 10.1088/1674-1056/ad2607

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Ferroelectric materials are promising candidates for ultraviolet photodetectors due to their ferroelectric effect. In this work, a BaTiO₃/p-GaN/Au hybrid heterojunction—Schottky self-driven ultraviolet photodetector was fabricated with excellent bipolar photoresponse property. At 0 V bias, the direction of the photocurrent can be switched by flipping the depolarization field of BaTiO₃, which allows the performance of photodetectors to be controlled by the ferroelectric effect. Meanwhile, a relatively large responsivity and a fast response speed can be also observed. In particular, when the depolarization field of BaTiO₃ is in the same direction of the built-in electric field of the Au/p-GaN Schottky junction (up polarized state), the photodetector exhibits a high responsivity of 18 mA/W at 360 nm, and a fast response speed of < 40 ms at 0 V. These findings pave a new way for the preparation of high-performance photodetectors with bipolar photocurrents.

Stable photocurrent—voltage characteristics of perovskite single crystal detectors obtained by pulsed bias Suggested by editors

Xin Liu(刘新), Zhi-Long Chen(陈之龙), Hu Wang(王虎), Wen-Qing Zhang(张雯清), Hao Dong(董昊), Peng-Xiang Wang(王鹏祥), and Yu-Chuan Shao(邵宇川)

Chin. Phys. B, 2024, 33 (4): 048101. DOI: 10.1088/1674-1056/ad23d7

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Photocurrent—voltage characterization is a crucial method for assessing key parameters in x-ray or γ -ray semiconductor detectors, especially the carrier mobility lifetime product. However, the high biases during photocurrent measurements tend to cause severe ion migration, which can lead to the instability and inaccuracy of the test results. Given the mixed electronic—ionic characteristics, it is imperative to devise novel methods capable of precisely measuring photocurrent—voltage characteristics under high bias conditions, free from interference caused by ion migration. In this paper, pulsed bias is employed to explore the photocurrent—voltage characteristics of MAPbBr₃ single crystals. The method yields stable photocurrent—voltage characteristics at a pulsed bias of up to 30 V, proving to be effective in mitigating ion migration. Through fitting the modified Hecht equation, we determined the mobility lifetime products of 1.0×10^-2 cm²· V^-1 for hole and 2.78×10^-3 cm²· V^-1 for electron. This approach offers a promising solution for accurately measuring the transport properties of carriers in perovskite.

Quantum control based on three forms of Lyapunov functions

Guo-Hui Yu(俞国慧) and Hong-Li Yang(杨洪礼)

Chin. Phys. B, 2024, 33 (4): 040201. DOI: 10.1088/1674-1056/ad11e6

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This paper introduces the quantum control of Lyapunov functions based on the state distance, the mean of imaginary quantities and state errors. In this paper, the specific control laws under the three forms are given. Stability is analyzed by the LaSalle invariance principle and the numerical simulation is carried out in a 2D test system. The calculation process for the Lyapunov function is based on a combination of the average of virtual mechanical quantities, the particle swarm algorithm and a simulated annealing algorithm. Finally, a unified form of the control laws under the three forms is given.

Higher-dimensional Chen—Lee—Liu equation and asymmetric peakon soliton Suggested by editors

Qiao-Hong Han(韩巧红) and Man Jia(贾曼)

Chin. Phys. B, 2024, 33 (4): 040202. DOI: 10.1088/1674-1056/ad1822

Abstract ( 132 )

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Integrable systems play a crucial role in physics and mathematics. In particular, the traditional (1+1)-dimensional and (2+1)-dimensional integrable systems have received significant attention due to the rarity of integrable systems in higher dimensions. Recent studies have shown that abundant higher-dimensional integrable systems can be constructed from (1+1)-dimensional integrable systems by using a deformation algorithm. Here we establish a new (2+1)-dimensional Chen—Lee—Liu (C—L—L) equation using the deformation algorithm from the (1+1)-dimensional C—L—L equation. The new system is integrable with its Lax pair obtained by applying the deformation algorithm to that of the (1+1)-dimension. It is challenging to obtain the exact solutions for the new integrable system because the new system combines both the original C—L—L equation and its reciprocal transformation. The traveling wave solutions are derived in implicit function expression, and some asymmetry peakon solutions are found.

Thermal-contact capacity of one-dimensional attractive Gaudin—Yang model

Xiao-Min Zhang(张小敏), Song Cheng(程颂), and Yang-Yang Chen(陈洋洋)

Chin. Phys. B, 2024, 33 (4): 040203. DOI: 10.1088/1674-1056/ad21f4

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Tan's contact $\mathcal{C}$ is an important quantity measuring the two-body correlations at short distances in a dilute system. Here we make use of the technique of exactly solved models to study the thermal-contact capacity $\mathcal{K}_{\scriptscriptstyle{\rm T}}$, i.e., the derivative of $\mathcal{C}$ with respect to temperature in the attractive Gaudin—Yang model. It is found that $\mathcal{K}_{\scriptscriptstyle{\rm T}}$ is useful in identifying the low temperature phase diagram, and using the obtained analytical expression of $\mathcal{K}_{\scriptscriptstyle{\rm T}}$, we study its critical behavior and the scaling law. Especially, we show $\mathcal{K}_{\scriptscriptstyle{\rm T}}$ versus temperature and thus the non-monotonic tendency of $\mathcal{C}$ in a tiny interval, for both spin-balanced and imbalanced phases. Such a phenomenon is merely observed in multi-component systems such as $SU(2)$ Fermi gases and spinor bosons, indicating the crossover from the Tomonaga—Luttinger liquid to the spin-coherent liquid.

Observer-based dynamic event-triggered control for distributed parameter systems over mobile sensor-plus-actuator networks

Wenying Mu(穆文英), Bo Zhuang(庄波), and Fang Qiu(邱芳)

Chin. Phys. B, 2024, 33 (4): 040204. DOI: 10.1088/1674-1056/ad1a8c

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We develop a policy of observer-based dynamic event-triggered state feedback control for distributed parameter systems over a mobile sensor-plus-actuator network. It is assumed that the mobile sensing devices that provide spatially averaged state measurements can be used to improve state estimation in the network. For the purpose of decreasing the update frequency of controller and unnecessary sampled data transmission, an efficient dynamic event-triggered control policy is constructed. In an event-triggered system, when an error signal exceeds a specified time-varying threshold, it indicates the occurrence of a typical event. The global asymptotic stability of the event-triggered closed-loop system and the boundedness of the minimum inter-event time can be guaranteed. Based on the linear quadratic optimal regulator, the actuator selects the optimal displacement only when an event occurs. A simulation example is finally used to verify that the effectiveness of such a control strategy can enhance the system performance.

Target layer state estimation in multi-layer complex dynamical networks considering nonlinear node dynamics Suggested by editors

Yayong Wu(吴亚勇), Xinwei Wang(王欣伟), and Guo-Ping Jiang(蒋国平)

Chin. Phys. B, 2024, 33 (4): 040205. DOI: 10.1088/1674-1056/ad20d7

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In many engineering networks, only a part of target state variables are required to be estimated. On the other hand, multi-layer complex network exists widely in practical situations. In this paper, the state estimation of target state variables in multi-layer complex dynamical networks with nonlinear node dynamics is studied. A suitable functional state observer is constructed with the limited measurement. The parameters of the designed functional observer are obtained from the algebraic method and the stability of the functional observer is proven by the Lyapunov theorem. Some necessary conditions that need to be satisfied for the design of the functional state observer are obtained. Different from previous studies, in the multi-layer complex dynamical network with nonlinear node dynamics, the proposed method can estimate the state of target variables on some layers directly instead of estimating all the individual states. Thus, it can greatly reduce the placement of observers and computational cost. Numerical simulations with the three-layer complex dynamical network composed of three-dimensional nonlinear dynamical nodes are developed to verify the effectiveness of the method.

Cryptanalysis of efficient semi-quantum secret sharing protocol using single particles

Gan Gao(高甘)

Chin. Phys. B, 2024, 33 (4): 040301. DOI: 10.1088/1674-1056/ad2bee

Abstract ( 156 )

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In paper [Chin. Phys. B 32 070308 (2023)], Xing et al. proposed a semi-quantum secret sharing protocol by using single particles. We study the security of the proposed protocol and find that it is not secure, that is, the three dishonest agents, Bob, Charlie and Emily can collude to obtain Alice's secret without the help of David.

Integer multiple quantum image scaling based on NEQR and bicubic interpolation

Shuo Cai(蔡硕), Ri-Gui Zhou(周日贵), Jia Luo(罗佳), and Si-Zhe Chen(陈思哲)

Chin. Phys. B, 2024, 33 (4): 040302. DOI: 10.1088/1674-1056/ad1b40

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As a branch of quantum image processing, quantum image scaling has been widely studied. However, most of the existing quantum image scaling algorithms are based on nearest-neighbor interpolation and bilinear interpolation, the quantum version of bicubic interpolation has not yet been studied. In this work, we present the first quantum image scaling scheme for bicubic interpolation based on the novel enhanced quantum representation (NEQR). Our scheme can realize synchronous enlargement and reduction of the image with the size of 2ⁿ×2ⁿ by integral multiple. Firstly, the image is represented by NEQR and the original image coordinates are obtained through multiple CNOT modules. Then, 16 neighborhood pixels are obtained by quantum operation circuits, and the corresponding weights of these pixels are calculated by quantum arithmetic modules. Finally, a quantum matrix operation, instead of a classical convolution operation, is used to realize the sum of convolution of these pixels. Through simulation experiments and complexity analysis, we demonstrate that our scheme achieves exponential speedup over the classical bicubic interpolation algorithm, and has better effect than the quantum version of bilinear interpolation.

Analysis of learnability of a novel hybrid quantum—classical convolutional neural network in image classification

Tao Cheng(程涛), Run-Sheng Zhao(赵润盛), Shuang Wang(王爽), Rui Wang(王睿), and Hong-Yang Ma(马鸿洋)

Chin. Phys. B, 2024, 33 (4): 040303. DOI: 10.1088/1674-1056/ad1926

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We design a new hybrid quantum—classical convolutional neural network (HQCCNN) model based on parameter quantum circuits. In this model, we use parameterized quantum circuits (PQCs) to redesign the convolutional layer in classical convolutional neural networks, forming a new quantum convolutional layer to achieve unitary transformation of quantum states, enabling the model to more accurately extract hidden information from images. At the same time, we combine the classical fully connected layer with PQCs to form a new hybrid quantum—classical fully connected layer to further improve the accuracy of classification. Finally, we use the MNIST dataset to test the potential of the HQCCNN. The results indicate that the HQCCNN has good performance in solving classification problems. In binary classification tasks, the classification accuracy of numbers 5 and 7 is as high as 99.71%. In multivariate classification, the accuracy rate also reaches 98.51%. Finally, we compare the performance of the HQCCNN with other models and find that the HQCCNN has better classification performance and convergence speed.

Quantum generative adversarial networks based on a readout error mitigation method with fault tolerant mechanism

Run-Sheng Zhao(赵润盛), Hong-Yang Ma(马鸿洋), Tao Cheng(程涛), Shuang Wang(王爽), and Xing-Kui Fan(范兴奎)

Chin. Phys. B, 2024, 33 (4): 040304. DOI: 10.1088/1674-1056/ad02e7

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Readout errors caused by measurement noise are a significant source of errors in quantum circuits, which severely affect the output results and are an urgent problem to be solved in noisy-intermediate scale quantum (NISQ) computing. In this paper, we use the bit-flip averaging (BFA) method to mitigate frequent readout errors in quantum generative adversarial networks (QGAN) for image generation, which simplifies the response matrix structure by averaging the qubits for each random bit-flip in advance, successfully solving problems with high cost of measurement for traditional error mitigation methods. Our experiments were simulated in Qiskit using the handwritten digit image recognition dataset under the BFA-based method, the Kullback—Leibler (KL) divergence of the generated images converges to 0.04, 0.05, and 0.1 for readout error probabilities of p=0.01, p=0.05, and p=0.1, respectively. Additionally, by evaluating the fidelity of the quantum states representing the images, we observe average fidelity values of 0.97, 0.96, and 0.95 for the three readout error probabilities, respectively. These results demonstrate the robustness of the model in mitigating readout errors and provide a highly fault tolerant mechanism for image generation models.

Coherence of nonlinear Bloch dynamics of Bose—Einstein condensates in deep optical lattices

Ai-Xia Zhang(张爱霞), Wei Zhang(张薇), Jie Wang(王杰), Xiao-Wen Hu(胡潇文), Lai-Lai Mi(米来来), and Ju-Kui Xue(薛具奎)

Chin. Phys. B, 2024, 33 (4): 040305. DOI: 10.1088/1674-1056/ad1b46

Abstract ( 86 )

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Atomic interaction leads to dephasing and damping of Bloch oscillations (BOs) in optical lattices, which limits observation and applications of BOs. How to obtain persistent BOs is particularly important. Here, the nonlinear Bloch dynamics of the Bose—Einstein condensate with two-body and three-body interactions in deep optical lattices is studied. The damping rate induced by interactions is obtained. The damping induced by two-body interaction plays a dominant role, while the damping induced by three-body interaction is weak. However, when the two-body and three-body interactions satisfy a threshold, long-lived coherent BOs are observed. Furthermore, the Bloch dynamics with periodical modulation of linear force is studied. The frequencies of linear force corresponding to resonance and pseudoresonance are obtained, and rich dynamical phenomena, i.e., stable and strong BOs, drifting and dispersion of wave packet, are predicted. The controllable Bloch dynamics is provided with the periodic modulation of the linear force.

Double quantum images encryption scheme based on chaotic system

She-Xiang Jiang(蒋社想), Yang Li(李杨), Jin Shi(石锦), and Ru Zhang(张茹)

Chin. Phys. B, 2024, 33 (4): 040306. DOI: 10.1088/1674-1056/ad1174

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This paper explores a double quantum images representation (DNEQR) model that allows for simultaneous storage of two digital images in a quantum superposition state. Additionally, a new type of two-dimensional hyperchaotic system based on sine and logistic maps is investigated, offering a wider parameter space and better chaotic behavior compared to the sine and logistic maps. Based on the DNEQR model and the hyperchaotic system, a double quantum images encryption algorithm is proposed. Firstly, two classical plaintext images are transformed into quantum states using the DNEQR model. Then, the proposed hyperchaotic system is employed to iteratively generate pseudo-random sequences. These chaotic sequences are utilized to perform pixel value and position operations on the quantum image, resulting in changes to both pixel values and positions. Finally, the ciphertext image can be obtained by qubit-level diffusion using two XOR operations between the position-permutated image and the pseudo-random sequences. The corresponding quantum circuits are also given. Experimental results demonstrate that the proposed scheme ensures the security of the images during transmission, improves the encryption efficiency, and enhances anti-interference and anti-attack capabilities.

Recurrent neural network decoding of rotated surface codes based on distributed strategy

Fan Li(李帆), Ao-Qing Li(李熬庆), Qi-Di Gan(甘启迪), and Hong-Yang Ma(马鸿洋)

Chin. Phys. B, 2024, 33 (4): 040307. DOI: 10.1088/1674-1056/ad2bef

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Quantum error correction is a crucial technology for realizing quantum computers. These computers achieve fault-tolerant quantum computing by detecting and correcting errors using decoding algorithms. Quantum error correction using neural network-based machine learning methods is a promising approach that is adapted to physical systems without the need to build noise models. In this paper, we use a distributed decoding strategy, which effectively alleviates the problem of exponential growth of the training set required for neural networks as the code distance of quantum error-correcting codes increases. Our decoding algorithm is based on renormalization group decoding and recurrent neural network decoder. The recurrent neural network is trained through the ResNet architecture to improve its decoding accuracy. Then we test the decoding performance of our distributed strategy decoder, recurrent neural network decoder, and the classic minimum weight perfect matching (MWPM) decoder for rotated surface codes with different code distances under the circuit noise model, the thresholds of these three decoders are about 0.0052, 0.0051, and 0.0049, respectively. Our results demonstrate that the distributed strategy decoder outperforms the other two decoders, achieving approximately a 5 % improvement in decoding efficiency compared to the MWPM decoder and approximately a 2 % improvement compared to the recurrent neural network decoder.

Non-Gaussian quantum states generated via quantum catalysis and their statistical properties

Xiao-Yan Zhang(张晓燕), Chun-Yan Yang(杨春燕), Ji-Suo Wang(王继锁), and Xiang-Guo Meng(孟祥国)

Chin. Phys. B, 2024, 33 (4): 040308. DOI: 10.1088/1674-1056/ad2a74

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A new kind of non-Gaussian quantum catalyzed state is proposed via multiphoton measurements and two-mode squeezing as an input of thermal state. The characteristics of the generated multiphoton catalysis output state depends on the thermal parameter, catalyzed photon number and squeezing parameter. We then analyze the nonclassical properties by examining the photon number distribution, photocount distribution and partial negativity of the Wigner function. Our findings indicate that nonclassicality can be achieved through the implementation of multiphoton catalysis operations and modulated by the thermal parameter, catalyzed photon number and squeezing parameter.

Harmonic balance simulation of the influence of component uniformity and reliability on the performance of a Josephson traveling wave parametric amplifier

Yuzhen Zheng(郑煜臻), Kanglin Xiong(熊康林), Jiagui Feng(冯加贵), and Hui Yang(杨辉)

Chin. Phys. B, 2024, 33 (4): 040401. DOI: 10.1088/1674-1056/ad0624

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A Josephson traveling wave parametric amplifier (JTWPA), which is a quantum-limited amplifier with high gain and large bandwidth, is the core device of large-scale measurement and control systems for quantum computing. A typical JTWPA consists of thousands of Josephson junctions connected in series to form a transmission line and hundreds of shunt LC resonators periodically loaded along the line for phase matching. Because the variation of these capacitors and inductors can be detrimental to their high-frequency characteristics, the fabrication of a JTWPA typically necessitates precise processing equipment. To guide the fabrication process and further improve the design for manufacturability, it is necessary to understand how each electronic component affects the amplifier. In this paper, we use the harmonic balance method to conduct a comprehensive study on the impact of nonuniformity and fabrication yield of the electronic components on the performance of a JTWPA. The results provide insightful and scientific guidance for device design and fabrication processes.

Thermodynamics in a quantum corrected Reissner—Nordström—AdS black hole and its GUP-corrections

Jian-Jun Song(宋建君) and Cheng-Zhou Liu(刘成周)

Chin. Phys. B, 2024, 33 (4): 040402. DOI: 10.1088/1674-1056/ad1a8a

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We calculate the thermodynamic quantities in the quantum corrected Reissner—Nordström—AdS (RN-AdS) black hole, and examine their quantum corrections. By analyzing the mass and heat capacity, we give the critical state and the remnant state, respectively, and discuss their consistency. Then, we investigate the quantum tunneling from the event horizon of massless scalar particle by using the null geodesic method, and charged massive boson W^± and fermions by using the Hamilton—Jacob method. It is shown that the same Hawking temperature can be obtained from these tunneling processes of different particles and methods. Next, by using the generalized uncertainty principle (GUP), we study the quantum corrections to the tunneling and the temperature. Then the logarithmic correction to the black hole entropy is obtained.

View of thermodynamic phase transition of the charged Gauss—Bonnet AdS black hole via the shadow

Ke-Jian He(何柯腱), Sen Guo(郭森), Zhi Luo(罗智), and Guo-Ping Li(李国平)

Chin. Phys. B, 2024, 33 (4): 040403. DOI: 10.1088/1674-1056/ad225d

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We examine thermodynamic phase transition (PT) of the charged Gauss—Bonnet AdS black hole (BH) by utilizing the shadow radius. In this system, we rescale the corresponding Gauss—Bonnet coefficient α by a factor of 1/(D-4), and ensure that α is positive to avoid any singularity problems. The equation derived for the shadow radius indicates that it increases as the event horizon radius increases, making it an independent variable for determining BH temperature. By investigating the PT curve in relation to shadows, we can observe that the shadow radius can be used as an alternative to the event horizon radius in explaining the phenomenon of BH PT. Furthermore, the results indicate that an increase in the parameter α corresponds to a decrease in the temperature of the BH. By utilizing the relationship between the temperature and the shadow radius, it is possible to obtain the thermal profile of the Gauss—Bonnet AdS BH. It is evident that there is an N-type variation in temperature for pressures P<P_c. Additionally, as the parameter α increases, the region covered by shadow expands while the temperature decreases. The utilization of BH shadows as a probe holds immense significance in gaining a deeper understanding of BH thermodynamic behavior.

Computing large deviation prefactors of stochastic dynamical systems based on machine learning

Yang Li(李扬), Shenglan Yuan(袁胜兰), Linghongzhi Lu(陆凌宏志), and Xianbin Liu(刘先斌)

Chin. Phys. B, 2024, 33 (4): 040501. DOI: 10.1088/1674-1056/ad12a8

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We present a large deviation theory that characterizes the exponential estimate for rare events in stochastic dynamical systems in the limit of weak noise. We aim to consider a next-to-leading-order approximation for more accurate calculation of the mean exit time by computing large deviation prefactors with the aid of machine learning. More specifically, we design a neural network framework to compute quasipotential, most probable paths and prefactors based on the orthogonal decomposition of a vector field. We corroborate the higher effectiveness and accuracy of our algorithm with two toy models. Numerical experiments demonstrate its powerful functionality in exploring the internal mechanism of rare events triggered by weak random fluctuations.

Influencer identification of dynamical networks based on an information entropy dimension reduction method

Dong-Li Duan(段东立), Si-Yuan Ji(纪思源), and Zi-Wei Yuan(袁紫薇)

Chin. Phys. B, 2024, 33 (4): 040502. DOI: 10.1088/1674-1056/ad102e

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Identifying critical nodes or sets in large-scale networks is a fundamental scientific problem and one of the key research directions in the fields of data mining and network science when implementing network attacks, defense, repair and control. Traditional methods usually begin from the centrality, node location or the impact on the largest connected component after node destruction, mainly based on the network structure. However, these algorithms do not consider network state changes. We applied a model that combines a random connectivity matrix and minimal low-dimensional structures to represent network connectivity. By using mean field theory and information entropy to calculate node activity, we calculated the overlap between the random parts and fixed low-dimensional parts to quantify the influence of node impact on network state changes and ranked them by importance. We applied this algorithm and the proposed importance algorithm to the overall analysis and stratified analysis of the C. elegans neural network. We observed a change in the critical entropy of the network state and by utilizing the proposed method we can calculate the nodes that indirectly affect muscle cells through neural layers.

Emergent topological ordered phase for the Ising-XY model revealed by cluster-updating Monte Carlo method Suggested by editors

Heyang Ma(马赫阳), Wanzhou Zhang(张万舟), Yanting Tian(田彦婷), Chengxiang Ding(丁成祥), and Youjin Deng(邓友金)

Chin. Phys. B, 2024, 33 (4): 040503. DOI: 10.1088/1674-1056/ad1d4d

Abstract ( 130 )

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The two-component cold atom systems with anisotropic hopping amplitudes can be phenomenologically described by a two-dimensional Ising-XY coupled model with spatial anisotropy. At low temperatures, theoretical predictions [Phys. Rev. A 72 053604 (2005)] and [arXiv: 0706.1609] indicate the existence of a topological ordered phase characterized by Ising and XY disorder but with 2XY ordering. However, due to ergodic difficulties faced by Monte Carlo methods at low temperatures, this topological phase has not been numerically explored. We propose a linear cluster updating Monte Carlo method, which flips spins without rejection in the anisotropy limit but does not change the energy. Using this scheme and conventional Monte Carlo methods, we succeed in revealing the nature of topological phases with half-vortices and domain walls. In the constructed global phase diagram, Ising and XY-type transitions are very close to each other and differ significantly from the schematic phase diagram reported earlier. We also propose and explore a wide range of quantities, including magnetism, superfluidity, specific heat, susceptibility, and even percolation susceptibility, and obtain consistent and reliable results. Furthermore, we observed first-order transitions characterized by common intersection points in magnetizations for different system sizes, as opposed to the conventional phase transition where Binder cumulants of various sizes share common intersections. The critical exponents of different types of phase transitions are reasonably fitted. The results are useful to help cold atom experiments explore the half-vortex topological phase.

Chimera states of phase oscillator populations with nonlocal higher-order couplings Suggested by editors

Yonggang Wu(伍勇刚), Huajian Yu(余华健), Zhigang Zheng(郑志刚), and Can Xu(徐灿)

Chin. Phys. B, 2024, 33 (4): 040504. DOI: 10.1088/1674-1056/ad1481

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The chimera states underlying many realistic dynamical processes have attracted ample attention in the area of dynamical systems. Here, we generalize the Kuramoto model with nonlocal coupling incorporating higher-order interactions encoded with simplicial complexes. Previous works have shown that higher-order interactions promote coherent states. However, we uncover the fact that the introduced higher-order couplings can significantly enhance the emergence of the incoherent state. Remarkably, we identify that the chimera states arise as a result of multi-attractors in dynamic states. Importantly, we review that the increasing higher-order interactions can significantly shape the emergent probability of chimera states. All the observed results can be well described in terms of the dimension reduction method. This study is a step forward in highlighting the importance of nonlocal higher-order couplings, which might provide control strategies for the occurrence of spatial—temporal patterns in networked systems.

Localized wave solutions and interactions of the (2+1)-dimensional Hirota—Satsuma—Ito equation Suggested by editors

Qiankun Gong(巩乾坤), Hui Wang(王惠), and Yunhu Wang(王云虎)

Chin. Phys. B, 2024, 33 (4): 040505. DOI: 10.1088/1674-1056/ad1f4c

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This paper studies the (2+1)-dimensional Hirota—Satsuma—Ito equation. Based on an associated Hirota bilinear form, lump-type solution, two types of interaction solutions, and breather wave solution of the (2+1)-dimensional Hirota—Satsuma—Ito equation are obtained, which are all related to the seed solution of the equation. It is interesting that the rogue wave is aroused by the interaction between one-lump soliton and a pair of resonance stripe solitons, and the fusion and fission phenomena are also found in the interaction between lump solitons and one-stripe soliton. Furthermore, the breather wave solution is also obtained by reducing the two-soliton solutions. The trajectory and period of the one-order breather wave are analyzed. The corresponding dynamical characteristics are demonstrated by the graphs.

Dynamics analysis and cryptographic implementation of a fractional-order memristive cellular neural network model

Xinwei Zhou(周新卫), Donghua Jiang(蒋东华), Jean De Dieu Nkapkop, Musheer Ahmad, Jules Tagne Fossi, Nestor Tsafack, and Jianhua Wu(吴建华)

Chin. Phys. B, 2024, 33 (4): 040506. DOI: 10.1088/1674-1056/ad03dd

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Due to the fact that a memristor with memory properties is an ideal electronic component for implementation of the artificial neural synaptic function, a brand-new tristable locally active memristor model is first proposed in this paper. Here, a novel four-dimensional fractional-order memristive cellular neural network (FO-MCNN) model with hidden attractors is constructed to enhance the engineering feasibility of the original CNN model and its performance. Then, its hardware circuit implementation and complicated dynamic properties are investigated on multi-simulation platforms. Subsequently, it is used toward secure communication application scenarios. Taking it as the pseudo-random number generator (PRNG), a new privacy image security scheme is designed based on the adaptive sampling rate compressive sensing (ASR-CS) model. Eventually, the simulation analysis and comparative experiments manifest that the proposed data encryption scheme possesses strong immunity against various security attack models and satisfactory compression performance.

A redundant subspace weighting procedure for clock ensemble

Hai Xu(徐海), Yu Chen(陈煜), Mo-Chi Liu(刘默驰), and Yu-Zhuo Wang(王玉琢)

Chin. Phys. B, 2024, 33 (4): 040601. DOI: 10.1088/1674-1056/ad1b43

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A redundant-subspace-weighting (RSW)-based approach is proposed to enhance the frequency stability on a time scale of a clock ensemble. In this method, multiple overlapping subspaces are constructed in the clock ensemble, and the weight of each clock in this ensemble is defined by using the spatial covariance matrix. The superimposition average of covariances in different subspaces reduces the correlations between clocks in the same laboratory to some extent. After optimizing the parameters of this weighting procedure, the frequency stabilities of virtual clock ensembles are significantly improved in most cases.

Low-energy inelastic electron scattering from carbon monoxide: Excitation and de-excitation of the X¹Σ⁺, a³Π, a'³Σ⁺, A¹Π, d³Δ, e³Σ-, I¹Σ- and D¹Δ electronic states

Pengyu Wei(卫鹏宇), Chaowen Huang(黄朝文), Xinlu Cheng(程新路), and Hong Zhang(张红)

Chin. Phys. B, 2024, 33 (4): 043101. DOI: 10.1088/1674-1056/ad123e

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Cross-sections for electronic excitation and de-excitation among the ground state and lowest-lying seven electronic excited states of carbon monoxide (CO) by low-energy electron impact are computed using the $R$-matrix method. The excitation cross-sections from the ground state to the electronic states ${\rm a}^{3}\Pi $, ${\rm a}^{\prime 3}\Sigma^{+}$ and ${\rm A}^{1}\Pi $ agree with previous experimental and theoretical results. In addition, the cross-sections for the ${\rm I}^{1}\Sigma^{-}$ and ${\rm D}^{1}\Delta $ states of CO, which will cascade to CO ${\rm a}^{\prime 3}\Sigma^{+}$ and ${\rm A}^{1}\Pi $ states, are calculated. Furthermore, in contrast to the typical increase in electronic excitation cross-sections with collision energy, the de-excitation cross-sections show a negative trend with increasing energy.

A proposal for detecting weak electromagnetic waves around 2.6 μm wavelength with Sr optical clock

Ruo-Shui Han(韩弱水), Wei Wang(王伟), and Tao Wang(汪涛)

Chin. Phys. B, 2024, 33 (4): 043201. DOI: 10.1088/1674-1056/ad1b45

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Infrared signal detection is widely used in many fields. Due to the detection principle, however, the accuracy and range of detection are limited. Thanks to the ultra stability of the ⁸⁷Sr optical lattice clock, external infrared electromagnetic wave disturbances can be responded to. Utilizing the ac Stark shift of the clock transition, we propose a new method to detect infrared signals. According to our calculations, the theoretical detection accuracy in the vicinity of its resonance band of 2.6 μm can reach the order of 10^-14 W, while the minimum detectable signal of common detectors is on the order of 10^-10 W.

Absolute partial and total ionization cross sections of carbon monoxide with electron collision from 350 eV to 8000 eV Suggested by editors

Taj Wali Khan, Weizhe Huang(黄伟哲), Enliang Wang(王恩亮), Xu Shan(单旭), and Xiangjun Chen(陈向军)

Chin. Phys. B, 2024, 33 (4): 043401. DOI: 10.1088/1674-1056/ad20dd

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The absolute partial and total cross sections for electron impact ionization of carbon monoxide are reported for electron energies from 350 eV to 8000 eV. The product ions (CO⁺, C⁺, O⁺, CO²⁺, C²⁺, and O²⁺) are measured by employing an ion imaging mass spectrometer and two ion-pair dissociation channels (C⁺ + O⁺ and C²⁺ + O⁺) are identified. The absolute cross sections for producing individual ions and their total, as well as for the ion-pair dissociation channels are obtained by normalizing the data of CO⁺ to that of Ar⁺ from CO—Ar mixture target with a fixed 1:1 ratio. The overall errors are evaluated by considering various kinds of uncertainties. A comprehensive comparison is made with the available data, which shows a good agreement with each other over the energy ranges that are overlapped. This work presents new cross-section data with electron energies above 1000 eV.

Accelerated generation of holograms with ultra-low memory symmetrically high-compressed look-up table

Yan Yang(杨燕), Jianying Zhu(朱建英), Minyuan Sun(孙敏远), and Yong Bi(毕勇)

Chin. Phys. B, 2024, 33 (4): 044201. DOI: 10.1088/1674-1056/ad1e67

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Computer-generated holography technology has been widely applied, and as research in this field deepens, the demand for memory and computational power in small AR and VR devices continues to increase. This paper presents a hologram generation method, i.e., a symmetrically high-compressed look-up table method, which can reduce memory usage by 50%. In offline computing, half of the basic horizontal and vertical modulation factors are stored, halving the memory requirements without affecting inline speed. Currently, its potential extends to various holographic applications, including the production of optical diffraction elements.

Effectively modulating spatial vortex four-wave mixing in a diamond atomic system

Nuo Ba(巴诺), Ming-Qi Jiang(姜明奇), Jin-You Fei(费金友), Dan Wang(王丹), Hai-Lin Jiang(蒋海林), Lei Wang(王磊), and Hai-Hua Wang(王海华)

Chin. Phys. B, 2024, 33 (4): 044202. DOI: 10.1088/1674-1056/ad0771

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Due to the spatial characteristics of orbital angular momentum, vortex fields can be applied in the fields of quantum storage and quantum information. We study the realization of spatially modulated vortex fields based on four-wave mixing in a four-level atomic system with a diamond structure. The intensity and spiral phase of the vortex field are effectively transferred to the generated four-wave mixing field. By changing the detuning of the probe field, the phase and intensity of the generated vertex four-wave mixing field can be changed. When the probe field takes a large detuning value, the spatial distribution of the intensity and phase of the vertex four-wave mixing field can be effectively tuned by adjusting the Rabi frequency or detuning value of the coupled field. At the same time, we also provide a detailed explanation based on the dispersion relationship, and the results agree well with our simulation results.

Topological edge and corner states of valley photonic crystals with zipper-like boundary conditions Suggested by editors

Yun-Feng Shen(沈云峰), Xiao-Fang Xu(许孝芳), Ming Sun(孙铭), Wen-Ji Zhou(周文佶), and Ya-Jing Chang(常雅箐)

Chin. Phys. B, 2024, 33 (4): 044203. DOI: 10.1088/1674-1056/ad1e6a

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We present a stable valley photonic crystal (VPC) unit cell with C_3v symmetric quasi-ring-shaped dielectric columns and realize its topological phase transition by breaking mirror symmetry. Based on this unit cell structure, topological edge states (TESs) and topological corner states (TCSs) are realized. We obtain a new type of wave transmission mode based on photonic crystal zipper-like boundaries and apply it to a beam splitter assembled from rectangular photonic crystals (PCs). The constructed beam splitter structure is compact and possesses frequency separation functions. In addition, we construct a box-shaped triangular PC structures with zipper-like boundaries and discover phenomena of TCSs in the corners, comparing its corner states with those formed by other boundaries. Based on this, we explore the regularities of the electric field patterns of TESs and TCSs, explain the connection between the characteristic frequencies and locality of TCSs, which helps better control photons and ensures low power consumption of the system.

Sensing the heavy water concentration in an H₂O—D₂O mixture by solid—solid phononic crystals

Mohammadreza Rahimi and Ali Bahrami

Chin. Phys. B, 2024, 33 (4): 044301. DOI: 10.1088/1674-1056/ad0bf5

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A new method based on phononic crystals is presented to detect the concentration of heavy water (D₂O) in an H₂O—D₂O mixture. Results have been obtained and analyzed in the concentration range of 0%—10% and 90%—100% D₂O. A proposed structure of tungsten scatterers in an aluminum host is studied. In order to detect the target material, a cavity region is considered as a sound wave resonator in which the target material with different concentrations of D₂O is embedded. By changing the concentration of D₂O in the H₂O—D₂O mixture, the resonance frequency undergoes a frequency shift. Each 1% change in D₂O concentration in the H₂O—D₂O mixture causes a frequency change of about 120 Hz. The finite element method is used as the numerical method to calculate and analyze the natural frequencies and transmission spectra of the proposed sensor. The performance evaluation index shows a high Q factor up to 1475758 and a high sensitivity up to 13075, which are acceptable values for sensing purposes. The other figures of merit related to the detection performance also indicate high-quality performance of the designed sensor.

Passive particles driven by self-propelled particle: The wake effect

Kai-Xuan Zheng(郑凯选), Jing-Wen Wang(汪静文), Shi-Feng Wang(王世锋), and De-Ming Nie(聂德明)

Chin. Phys. B, 2024, 33 (4): 044501. DOI: 10.1088/1674-1056/ad1a8d

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This work focuses on numerically studying hydrodynamic interaction between a passive particle and a self-propelled particle, termed a squirmer, by using a two-dimensional lattice Boltzmann method (LBM). It is found that the squirmer can capture a passive particle and propel it simultaneously, provided the passive particle is situated within the squirmer's wake. Our research shows that the critical capture distance, which determines whether the particle is captured, primarily depends on the intensity of the squirmer's dipolarity. The stronger dipolarity of squirmer results in an increased critical capture distance. Conversely, the Reynolds number is found to have minimal influence on this interaction. Interestingly, the passive particle, when driven by the squirmer's wake, contributes to a reduction in the squirmer's drag. This results in a mutual acceleration for both particles. Our findings can provide valuable perspectives for formulating the principles of reducing the drag of micro-swimmers and help to achieve the goal of using micro-swimmers to transport goods without physical tethers.

Effect of granular shape on radial segregation in a two-dimensional drum

Yue Xu(徐悦), Ran Li(李然), Zhipeng Chi(迟志鹏), Wenzheng Xiu(修文正), Qicheng Sun(孙其诚), and Hui Yang(杨晖)

Chin. Phys. B, 2024, 33 (4): 044502. DOI: 10.1088/1674-1056/ad1092

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Granular segregation is widely observed in nature and industry. Most research has focused on segregation caused by differences in the size and density of spherical grains. However, due to the fact that grains typically have different shapes, the focus is shifting towards shape segregation. In this study, experiments are conducted by mixing cubic and spherical grains. The results indicate that spherical grains gather at the center and cubic grains are distributed around them, and the degree of segregation is low. Through experiments, a structured analysis of local regions is conducted to explain the inability to form stable segregation patterns with obviously different geometric shapes. Further, through simulations, the reasons for the central and peripheral distributions are explained by comparing velocities and the number of collisions of the grains in the flow layer.

Molecular dynamics simulation of the flow mechanism of shear-thinning fluids in a microchannel

Gang Yang(杨刚), Ting Zheng(郑庭), Qihao Cheng(程启昊), and Huichen Zhang(张会臣)

Chin. Phys. B, 2024, 33 (4): 044701. DOI: 10.1088/1674-1056/ad08a7

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Shear-thinning fluids have been widely used in microfluidic systems, but their internal flow mechanism is still unclear. Therefore, in this paper, molecular dynamics simulations are used to study the laminar flow of shear-thinning fluid in a microchannel. We validated the feasibility of our simulation method by evaluating the mean square displacement and Reynolds number of the solution layers. The results show that the change rule of the fluid system's velocity profile and interaction energy can reflect the shear-thinning characteristics of the fluids. The velocity profile resembles a top-hat shape, intensifying as the fluid's power law index decreases. The interaction energy between the wall and the fluid decreases gradually with increasing velocity, and a high concentration of non-Newtonian fluid reaches a plateau sooner. Moreover, the velocity profile of the fluid is related to the molecule number density distribution and their values are inversely proportional. By analyzing the radial distribution function, we found that the hydrogen bonds between solute and water molecules weaken with the increase in velocity. This observation offers an explanation for the shear-thinning phenomenon of the non-Newtonian flow from a micro perspective.

Dynamic modeling of cavitation bubble clusters: Effects of evaporation, condensation, and bubble—bubble interaction Suggested by editors

Long Xu(许龙), Xin-Rui Yao(姚昕锐), and Yang Shen(沈阳)

Chin. Phys. B, 2024, 33 (4): 044702. DOI: 10.1088/1674-1056/ad181f

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We present a dynamic model of cavitation bubbles in a cluster, in which the effects of evaporation, condensation, and bubble—bubble interactions are taken into consideration. Under different ultrasound conditions, we examine how the dynamics of cavitation bubbles are affected by several factors, such as the locations of the bubbles, the ambient radius, and the number of bubbles. Herein the variations of bubble radius, energy, temperature, pressure, and the quantity of vapor molecules are analyzed. Our findings reveal that bubble—bubble interactions can restrict the expansion of bubbles, reduce the exchange of energy among vapor molecules, and diminish the maximum internal temperature and pressure when bursting. The ambient radius of bubbles can influence the intensities of their oscillations, with clusters comprised of smaller bubbles creating optimal conditions for generating high-temperature and high-pressure regions. Moreover, an increase in the number of bubbles can further inhibit cavitation activities. The frequency, pressure and waveform of the driving wave can also exert a significant influence on cavitation activities, with rectangular waves enhancing and triangular waves weakening the cavitation of bubbles in the cluster. These results provide a theoretical basis for understanding the dynamics of cavitation bubbles in a bubble cluster, and the factors that affect their behaviors.

Magnetic diagnostics layout design for CFETR plasma equilibrium reconstruction

Qingze Yu(于庆泽), Yao Huang(黄耀), Zhengping Luo(罗正平), Yuehang Wang(汪悦航), Zijie Liu(刘自结), Wangyi Rui(芮望颐), Kai Wu(吴凯), Bingjia Xiao(肖炳甲), and Jiangang Li(李建刚)

Chin. Phys. B, 2024, 33 (4): 045201. DOI: 10.1088/1674-1056/ad23d6

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Plasma equilibrium reconstruction provides essential information for tokamak operation and physical analysis. An extensive and reliable set of magnetic diagnostics is required to obtain accurate plasma equilibrium. This study designs and optimizes the magnetic diagnostics layout for the reconstruction of the equilibrium of the plasma according to the scientific objectives, engineering design parameters, and limitations of the Chinese Fusion Engineering Test Reactor (CFETR). Based on the CFETR discharge simulation, magnetic measurement data are employed to reconstruct consistent plasma equilibrium parameters, and magnetic diagnostics' number and position are optimized by truncated Singular value decomposition, verifying the redundancy reliability of the magnetic diagnostics layout design. This provides a design solution for the layout of the magnetic diagnostics system required to control the plasma equilibrium of CFETR, and the developed design and optimization method can provide effective support to design magnetic diagnostics systems for future magnetic confinement fusion devices.

Error field penetration in J-TEXT tokamak based on two-fluid drift-MHD model Suggested by editors

Wen Wang(王文), Tao Xu(徐涛), Yi Zhang(张仪), and the J-TEXT team

Chin. Phys. B, 2024, 33 (4): 045202. DOI: 10.1088/1674-1056/ad1e6b

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An externally generated resonant magnetic perturbation can induce complex non-ideal MHD responses in their resonant surfaces. We have studied the plasma responses using Fitzpatrick's improved two-fluid model and program LAYER. We calculated the error field penetration threshold for J-TEXT. In addition, we find that the island width increases slightly as the error field amplitude increases when the error field amplitude is below the critical penetration value. However, the island width suddenly jumps to a large value because the shielding effect of the plasma against the error field disappears after the penetration. By scanning the natural mode frequency, we find that the shielding effect of the plasma decreases as the natural mode frequency decreases. Finally, we obtain the m/n=2/1 penetration threshold scaling on density and temperature.

Influence of extraction voltage on electron and ion behavior characteristics

Ao Xu(徐翱), Pingping Gan(甘娉娉), Yuanjie Shi(石元杰), and Lei Chen(陈磊)

Chin. Phys. B, 2024, 33 (4): 045203. DOI: 10.1088/1674-1056/ad1820

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The characteristics of the extracted ion current have a significant impact on the design and testing of ion source performance. In this paper, a 2D in space and 3D in velocity space particle in cell (2D3V PIC) method is utilized to simulate plasma motion and ion extraction characteristics under various initial plasma velocity distributions and extraction voltages in a Cartesian coordinate system. The plasma density is of the order of 10¹⁵ m^-3—10¹⁶ m^-3 and the extraction voltage is of the order of 100 V—1000 V. The study investigates the impact of various extraction voltages on the velocity and density distributions of electrons and positive ions, and analyzes the influence of different initial plasma velocity distributions on the extraction current. The simulation results reveal that the main reason for the variation of extraction current is the space-charge force formed by the relative aggregation of positive and negative net charges. This lays the foundation for a deeper understanding of extraction beam characteristics.

Simulation of deuterium pellet ablation and deposition in the EAST tokamak with HPI2 code

Da-Zheng Li(李大正), Jie Zhang(张洁), Ji-Lei Hou(侯吉磊), Mao Li(李懋), and Ji-Zhong Sun(孙继忠)

Chin. Phys. B, 2024, 33 (4): 045204. DOI: 10.1088/1674-1056/ad1e68

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Pellet injection is a primary method for fueling the plasma in magnetic confinement devices. For that goal the knowledges of pellet ablation and deposition profiles are critical. In the present study, the pellet fueling code HPI2 was used to predict the ablation and deposition profiles of deuterium pellets injected into a typical H-mode discharge on the EAST tokamak. Pellet ablation and deposition profiles were evaluated for various pellet injection locations, with the aim at optimizing the pellet injection to obtain a deep fueling depth. In this study, we investigate the effect of the injection angle on the deposition depth of the pellet at different velocities and sizes. The ablation and deposition of the injected pellet are mainly studied at each injection position for three different injection angles: 0°, 45°, and 60°. The pellet injection on the high field side (HFS) can achieve a more ideal deposition depth than on the low field side (LFS). Among these angles, horizontal injection on the middle plane is relatively better on either the HFS or the LFS. When the injection location is 0.468 m below the middle plane on the HFS or 0.40 m above the middle plane of the LFS, it can achieve a similar deposition depth to the one of its corresponding side. When the pre-cooling effect is taken into account, the deposition depth is predicted to increase only slightly when the pellet is launched from the HFS. The findings of this study will serve as a reference for the update of pellet injection systems for the EAST tokamak.

Plasma potential measurements using an emissive probe made of oxide cathode

Jian-Quan Li(李建泉), Hai-Jie Ma(马海杰), and Wen-Qi Lu(陆文琪)

Chin. Phys. B, 2024, 33 (4): 045205. DOI: 10.1088/1674-1056/ad1821

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A novel emissive probe consisting of an oxide cathode coating is developed to achieve a low operating temperature and long service life. The properties of the novel emissive probe are investigated in detail, in comparison with a traditional tungsten emissive probe, including the operating temperature, the electron emission capability and the plasma potential measurement. Studies of the operating temperature and electron emission capability show that the tungsten emissive probe usually works at a temperature of 1800 K—2200 K while the oxide cathode emissive probe can function at about 1200 K—1400 K. In addition, plasma potential measurements using the oxide cathode emissive probe with different techniques have been accomplished in microwave electron cyclotron resonance plasmas with different discharge powers. It is found that a reliable plasma potential can be obtained using the improved inflection point method and the hot probe with zero emission limit method, while the floating point method is invalid for the oxide cathode emissive probe.

Stability and melting behavior of boron phosphide under high pressure Suggested by editors

Wenjia Liang(梁文嘉), Xiaojun Xiang(向晓君), Qian Li(李倩), Hao Liang(梁浩), and Fang Peng(彭放)

Chin. Phys. B, 2024, 33 (4): 046201. DOI: 10.1088/1674-1056/ad23d4

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Boron phosphide (BP) has gained significant research attention due to its unique photoelectric and mechanical properties. In this work, we investigated the stability of BP under high pressure using x-ray diffraction and scanning electron microscope. The phase diagram of BP was explored in both B-rich and P-rich environments, revealing crucial insight into its behavior at 5.0 GPa. Additionally, we measured the melting curve of BP from 8.0 GPa to 15.0 GPa. Our findings indicate that the stability of BP under high pressure is improved within B-rich and P-rich environments. Furthermore, we report a remarkable observation of melting curve frustration at 10.0 GPa. This study will enhance our understanding of stability of BP under high pressure, shedding light on its potential application in semiconductor, thermal, and light-transmitting devices.

In situ observation of the phase transformation kinetics of bismuth during shock release

Jiangtao Li(李江涛), Qiannan Wang(王倩男), Liang Xu(徐亮), Lei Liu(柳雷), Hang Zhang(张航), Sota Takagi, Kouhei Ichiyanagi, Ryo Fukaya, Shunsuke Nozawa, and Jianbo Hu(胡建波)

Chin. Phys. B, 2024, 33 (4): 046401. DOI: 10.1088/1674-1056/ad0ec6

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A time-resolved x-ray diffraction technique is employed to monitor the structural transformation of laser-shocked bismuth. Results reveal a retarded transformation from the shock-induced Bi-V phase to a metastable Bi-IV phase during the shock release, instead of the thermodynamically stable Bi-III phase. The emergence of the metastable Bi-IV phase is understood by the competitive interplay between two transformation pathways towards the Bi-IV and Bi-III, respectively. The former is more rapid than the latter because the Bi-V to B-IV transformation is driven by interaction between the closest atoms while the Bi-V to B-III transformation requires interaction between the second-closest atoms. The nucleation time for the Bi-V to Bi-IV transformation is determined to be 5.1±0.9 ns according to a classical nucleation model. This observation demonstrates the importance of the formation of the transient metastable phases, which can change the phase transformation pathway in a dynamic process.

Local thermal conductivity of inhomogeneous nano-fluidic films:A density functional theory perspective

Zongli Sun(孙宗利), Yanshuang Kang(康艳霜), and Yanmei Kang(康艳梅)

Chin. Phys. B, 2024, 33 (4): 046503. DOI: 10.1088/1674-1056/ad18a9

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Combining the mean field Pozhar—Gubbins (PG) theory and the weighted density approximation, a novel method for local thermal conductivity of inhomogeneous fluids is proposed. The correlation effect that is beyond the mean field treatment is taken into account by the simulation-based empirical correlations. The application of this method to confined argon in slit pore shows that its prediction agrees well with the simulation results, and that it performs better than the original PG theory as well as the local averaged density model (LADM). In its further application to the nano-fluidic films, the influences of fluid parameters and pore parameters on the thermal conductivity are calculated and investigated. It is found that both the local thermal conductivity and the overall thermal conductivity can be significantly modulated by these parameters. Specifically, in the supercritical states, the thermal conductivity of the confined fluid shows positive correlation to the bulk density as well as the temperature. However, when the bulk density is small, the thermal conductivity exhibits a decrease-increase transition as the temperature is increased. This is also the case in which the temperature is low. In fact, the decrease—increase transition in both the small-bulk-density and low-temperature cases arises from the capillary condensation in the pore. Furthermore, smaller pore width and/or stronger adsorption potential can raise the critical temperature for condensation, and then are beneficial to the enhancement of the thermal conductivity. These modulation behaviors of the local thermal conductivity lead immediately to the significant difference of the overall thermal conductivity in different phase regions.

Microscopic growth mechanism and edge states of monolayer 1T'-MoTe₂ Suggested by editors

Haipeng Zhao(赵海鹏), Yin Liu(刘隐), Shengguo Yang(杨胜国), Chenfang Lin(林陈昉), Mingxing Chen(陈明星), Kai Braun, Xinyi Luo(罗心仪), Siyu Li(李思宇), Anlian Pan(潘安练), and Xiao Wang(王笑)

Chin. Phys. B, 2024, 33 (4): 046801. DOI: 10.1088/1674-1056/ad16d5

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Transition metal ditellurides (TMTDs) have versatile physical properties, including non-trivial topology, Weyl semimetal states and unique spin texture. Controlled growth of high-quality and large-scale monolayer TMTDs with preferred crystal phases is crucial for their applications. Here, we demonstrate the epitaxial growth of 1T'-MoTe₂ on Au (111) and graphitized silicon carbide (Gr/SiC) by molecular beam epitaxy (MBE). We investigate the morphology of the grown 1T'-MoTe₂ at the atomic level by scanning tunnelling microscopy (STM) and reveal the corresponding microscopic growth mechanism. It is found that the unique ordered Te structures preferentially deposited on Au (111) regulate the growth of monolayer single crystal 1T'-MoTe₂, while the Mo clusters were preferentially deposited on the Gr/SiC substrate, which impedes the ordered growth of monolayer MoTe₂. We confirm that the size of single crystal 1T'-MoTe₂ grown on Au (111) is nearly two orders of magnitude larger than that on Gr/SiC. By scanning tunnelling spectroscopy (STS), we observe that the STS spectrum of the monolayer 1T'-MoTe₂ nano-island at the edge is different from that at the interior, which exhibits enhanced conductivity.

Spin direction dependent quantum anomalous Hall effect in two-dimensional ferromagnetic materials

Yu-Xian Yang(杨宇贤) and Chang-Wen Zhang(张昌文)

Chin. Phys. B, 2024, 33 (4): 047101. DOI: 10.1088/1674-1056/ad1380

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We propose a scheme for realizing the spin direction-dependent quantum anomalous Hall effect (QAHE) driven by spin—orbit couplings (SOC) in two-dimensional (2D) materials. Based on the sp³ tight-binding (TB) model, we find that these systems can exhibit a QAHE with out-of-plane and in-plane magnetization for the weak and strong SOC, respectively, in which the mechanism of quantum transition is mainly driven by the band inversion of p_x,y/p_z orbitals. As a concrete example, based on first-principles calculations, we realize a real material of monolayer 1T-SnN₂/PbN₂ exhibiting the QAHE with in-plane/out-of-plane magnetization characterized by the nonzero Chern number C and topological edge states. These findings provide useful guidance for the pursuit of a spin direction-dependent QAHE and hence stimulate immediate experimental interest.

Research of caged dynamics of clusters center atoms in Pd₈₂Si₁₈ amorphous alloy Suggested by editors

Yong-He Deng(邓永和), Bei Chen(陈贝), Qing-Hua Qi(祁清华), Bing-Bing Li(李兵兵), Ming Gao(高明), Da-Dong Wen(文大东), Xiao-Yun Wang(王小云), and Ping Peng(彭平)

Chin. Phys. B, 2024, 33 (4): 047102. DOI: 10.1088/1674-1056/ad1d4e

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To date, there is still a lack of a comprehensive explanation for caged dynamics which is regarded as one of the intricate dynamic behaviors in amorphous alloys. This study focuses on Pd₈₂Si₁₈ as the research object to further elucidate the underlying mechanism of caged dynamics from multiple perspectives, including the cage's lifetime, atomic local environment, and atomic potential energy. The results reveal that Si atoms exhibit a pronounced cage effect due to the hindrance of Pd atoms, resulting in an anomalous peak in the non-Gaussian parameters. An in-depth investigation was conducted on the caged dynamics differences between fast and slow Si atoms. In comparison to fast Si atoms, slow Si atoms were surrounded by more Pd atoms and occupied lower potential energy states, resulting in smaller diffusion displacements for the slow Si atoms. Concurrently, slow Si atoms tend to be in the centers of smaller clusters with coordination numbers of 9 and 10. During the isothermal relaxation process, clusters with coordination numbers 9 and 10 have longer lifetimes, suggesting that the escape of slow Si atoms from their cages is more challenging. The findings mentioned above hold significant implications for understanding the caged dynamics.

Actively tuning anisotropic light—matter interaction in biaxial hyperbolic material α-MoO₃ using phase change material VO₂ and graphene

Kun Zhou(周昆), Yang Hu(胡杨), Biyuan Wu(吴必园), Xiaoxing Zhong(仲晓星), and Xiaohu Wu(吴小虎)

Chin. Phys. B, 2024, 33 (4): 047103. DOI: 10.1088/1674-1056/ad23d2

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Anisotropic hyperbolic phonon polaritons (PhPs) in natural biaxial hyperbolic material α-MoO₃ has opened up new avenues for mid-infrared nanophotonics, while active tunability of α-MoO₃ PhPs is still an urgent problem necessarily to be solved. In this study, we present a theoretical demonstration of actively tuning α-MoO₃ PhPs using phase change material VO₂ and graphene. It is observed that α-MoO₃ PhPs are greatly dependent on the propagation plane angle of PhPs. The insulator-to-metal phase transition of VO₂ has a significant effect on the hybridization PhPs of the α-MoO₃/VO₂ structure and allows to obtain actively tunable α-MoO₃ PhPs, which is especially obvious when the propagation plane angle of PhPs is 90°. Moreover, when graphene surface plasmon sources are placed at the top or bottom of α-MoO₃ in α-MoO₃/VO₂ structure, tunable coupled hyperbolic plasmon—phonon polaritons inside its Reststrahlen bands (RBs) and surface plasmon—phonon polaritons outside its RBs can be achieved. In addition, the above-mentioned α-MoO₃-based structures also lead to actively tunable anisotropic spontaneous emission (SE) enhancement. This study may be beneficial for realization of active tunability of both PhPs and SE of α-MoO₃, and facilitate a deeper understanding of the mechanisms of anisotropic light—matter interaction in α-MoO₃ using functional materials.

Anisotropic spin transport and photoresponse characteristics detected by tip movement in magnetic single-molecule junction

Deng-Hui Chen(陈登辉), Zhi Yang(羊志), Xin-Yu Fu(付新宇), Shen-Ao Qin(秦申奥), Yan Yan(严岩), Chuan-Kui Wang(王传奎), Zong-Liang Li(李宗良), and Shuai Qiu(邱帅)

Chin. Phys. B, 2024, 33 (4): 047201. DOI: 10.1088/1674-1056/ad1e65

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Orientation-dependent transport properties induced by anisotropic molecules are enticing in single-molecule junctions. Here, using the first-principles method, we theoretically investigate spin transport properties and photoresponse characteristics in trimesic acid magnetic single-molecule junctions with different molecular adsorption orientations and electrode contact sites. The transport calculations indicate that a single-molecule switch and a significant enhancement of spin transport and photoresponse can be achieved when the molecular adsorption orientation changes from planar geometry to upright geometry. The maximum spin polarization of current and photocurrent in upright molecular junctions exceeds 90%. Moreover, as the Ni tip electrode moves, the tunneling magnetoresistance of upright molecular junctions can be increased to 70%. The analysis of the spin-dependent PDOS elucidates that the spinterfaces between organic molecule and ferromagnetic electrodes are modulated by molecular adsorption orientation, where the molecule in upright molecular junctions yields higher spin polarization. Our theoretical work paves the way for designing spintronic devices and optoelectronic devices with anisotropic functionality base on anisotropic molecules.

Spin-polarized pairing induced by the magnetic field in the Bernal bilayer graphene Suggested by editors

Yan Huang(黄妍) and Tao Zhou(周涛)

Chin. Phys. B, 2024, 33 (4): 047403. DOI: 10.1088/1674-1056/ad102f

Abstract ( 113 )

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Recent experimental findings have demonstrated the occurrence of superconductivity in Bernal bilayer graphene when induced by a magnetic field. In this study, we conduct a theoretical investigation of the potential pairing symmetry within this superconducting system. By developing a theoretical model, we primarily calculate the free energy of the system with p+ip-wave parallel spin pairing, p+ip-wave anti-parallel spin pairing and d+id-wave pairing symmetry. Our results confirm that the magnetic field is indeed essential for generating the superconductivity. We discover that the p+ip-wave parallel spin pairing leads to a lower free energy for the system. The numerical calculations of the energy band structure, zero-energy spectral function and density of states for each of the three pairing symmetries under consideration show a strong consistency with the free energy results.

Analytical solutions to the precession relaxation of magnetization with uniaxial anisotropy

Ze-Nan Zhang(张泽南), Zhen-Lin Jia(贾镇林), and De-Sheng Xue(薛德胜)

Chin. Phys. B, 2024, 33 (4): 047502. DOI: 10.1088/1674-1056/ad08a3

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Based on the Landau--Lifshitz--Gilbert (LLG) equation, the precession relaxation of magnetization is studied when the external field ${{\bm H}}$ is parallel to the uniaxial anisotropic field ${{\bm H}}_{\rm k}$. The evolution of three-component magnetization is solved analytically under the condition of $H=nH_{\rm k}$ ($n =3$, 1 and 0). It is found that with an increase of ${{\bm H}}$ or a decrease of the initial polar angle of magnetization, the relaxation time decreases and the angular frequency of magnetization increases. For comparison, the analytical solution for $H_{\rm k}=0$ is also given. When the magnetization becomes stable, the angular frequency is proportional to the total effective field acting on the magnetization. The analytical solutions are not only conducive to the understanding of the precession relaxation of magnetization, but also can be used as a standard model to test the numerical calculation of LLG equation.

Wedge-shaped HfO₂ buffer layer-induced field-free spin—orbit torque switching of HfO₂/Pt/Co structure

Jian-Hui Chen(陈建辉), Meng-Fan Liang(梁梦凡), Yan Song(宋衍), Jun-Jie Yuan(袁俊杰), Meng-Yang Zhang(张梦旸), Yong-Ming Luo(骆泳铭), and Ning-Ning Wang(王宁宁)

Chin. Phys. B, 2024, 33 (4): 047503. DOI: 10.1088/1674-1056/ad1a88

Abstract ( 149 )

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Field-free spin—orbit torque (SOT) switching of perpendicular magnetization is essential for future spintronic devices. This study demonstrates the field-free switching of perpendicular magnetization in an HfO₂/Pt/Co/TaO_x structure, which is facilitated by a wedge-shaped HfO₂ buffer layer. The field-free switching ratio varies with HfO₂ thickness, reaching optimal performance at 25 nm. This phenomenon is attributed to the lateral anisotropy gradient of the Co layer, which is induced by the wedge-shaped HfO₂ buffer layer. The thickness gradient of HfO₂ along the wedge creates a corresponding lateral anisotropy gradient in the Co layer, correlating with the switching ratio. These findings indicate that field-free SOT switching can be achieved through designing buffer layer, offering a novel approach to innovating spin—orbit device.

Enhanced stability of FA-based perovskite: Rare-earth metal compound EuBr₂ doping Suggested by editors

Minna Hou(候敏娜), Xu Guo(郭旭), Meidouxue Han(韩梅斗雪), Juntao Zhao(赵均陶), Zhiyuan Wang(王志元), Yi Ding(丁毅), Guofu Hou(侯国付), Zongsheng Zhang(张宗胜), and Xiaoping Han(韩小平)

Chin. Phys. B, 2024, 33 (4): 047802. DOI: 10.1088/1674-1056/ad23d5

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It is highly desirable to enhance the long-term stability of perovskite solar cells (PSCs) so that this class of photovoltaic cells can be effectively used for the commercialization purposes. In this contribution, attempts have been made to use the two-step sequential method to dope EuBr₂ into FAMAPbI₃ perovskite to promote the stability. It is shown that the device durability at 85 ℃ in air with RH of 20%—40% is improved substantially, and simultaneously the champion device efficiency of 23.04% is achieved. The enhancement in stability is attributed to two points: (i) EuBr₂ doping effectively inhibits the decomposition and α—δ phase transition of perovskite under ambient environment, and (ii) EuBr₂ aggregates in the oxidized format of Eu(BrO₃)₃ at perovskite grain boundaries and surface, hampering humidity erosion and mitigates degradation through coordination with H₂O.

Physical mechanism of secondary-electron emission in Si wafers Suggested by editors

Yanan Zhao(赵亚楠), Xiangzhao Meng(孟祥兆), Shuting Peng(彭淑婷), Guanghui Miao(苗光辉), Yuqiang Gao(高玉强), Bin Peng(彭斌), Wanzhao Cui(崔万照), and Zhongqiang Hu(胡忠强)

Chin. Phys. B, 2024, 33 (4): 047901. DOI: 10.1088/1674-1056/ad1175

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CMOS-compatible RF/microwave devices, such as filters and amplifiers, have been widely used in wireless communication systems. However, secondary-electron emission phenomena often occur in RF/microwave devices based on silicon (Si) wafers, especially in the high-frequency range. In this paper, we have studied the major factors that influence the secondary-electron yield (SEY) in commercial Si wafers with different doping concentrations. We show that the SEY is suppressed as the doping concentration increases, corresponding to a relatively short effective escape depth λ. Meanwhile, the reduced narrow band gap is beneficial in suppressing the SEY, in which the absence of a shallow energy band below the conduction band will easily capture electrons, as revealed by first-principles calculations. Thus, the new physical mechanism combined with the effective escape depth and band gap can provide useful guidance for the design of integrated RF/microwave devices based on Si wafers.

Effect of external magnetic field on the instability of THz plasma waves in nanoscale graphene field-effect transistors Suggested by editors

Liping Zhang(张丽萍), Zongyao Sun(孙宗耀), Jiani Li(李佳妮), and Junyan Su(苏俊燕)

Chin. Phys. B, 2024, 33 (4): 048102. DOI: 10.1088/1674-1056/ad1e66

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The instability of plasma waves in the channel of field-effect transistors will cause the electromagnetic waves with THz frequency. Based on a self-consistent quantum hydrodynamic model, the instability of THz plasmas waves in the channel of graphene field-effect transistors has been investigated with external magnetic field and quantum effects. We analyzed the influence of weak magnetic fields, quantum effects, device size, and temperature on the instability of plasma waves under asymmetric boundary conditions numerically. The results show that the magnetic fields, quantum effects, and the thickness of the dielectric layer between the gate and the channel can increase the radiation frequency. Additionally, we observed that increase in temperature leads to a decrease in both oscillation frequency and instability increment. The numerical results and accompanying images obtained from our simulations provide support for the above conclusions.

Pre-existing orthorhombic embryos-induced hexagonal—orthorhombic martensitic transformation in MnNiSi_1-x(CoNiGe)_x alloy Suggested by editors

Ting-Ting Zhang(张婷婷), Yuan-Yuan Gong(龚元元), Zi-Qian Lu(鲁子骞), and Feng Xu(徐锋)

Chin. Phys. B, 2024, 33 (4): 048103. DOI: 10.1088/1674-1056/ad188d

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The thermal—elastic martensitic transformation from high-temperature Ni$_{2}$In-type hexagonal structure to low-temperature TiNiSi-type orthorhombic structure has been widely studied in Mn$MX$ ($M={\rm Ni}$ or Co, and $X={\rm Ge}$ or Si) alloys. However, the answer to how the orthorhombic martensite nucleates and grows within the hexagonal parent is still unclear. In this work, the hexagonal—orthorhombic martensitic transformation in a Co and Ge co-substituted MnNiSi is investigated. One can find some orthorhombic laths embedded in the hexagonal parent at a temperature above the martensitic transformation start temperature ($M_{\rm s}$). With the the sample cooing to $M_{\rm s}$, the laths turn broader, indicating that the martensitic transformation starts from these pre-existing orthorhombic laths. Microstructure observation suggests that these pre-existing orthorhombic laths do not originate from the hexagonal—orthorhombic martensitic transformation because of the difference between atomic occupations of doping elements in the hexagonal parent and those in the pre-existing orthorhombic laths. The phenomenological crystallographic theory and experimental investigations prove that the pre-existing orthorhombic lath and generated orthorhombic martensite have the same crystallography relationship to the hexagonal parent. Therefore, the orthorhombic martensite can take these pre-existing laths as embryos and grow up. This work implies that the martensitic transformation in MnNiSi$_{1-x}$(CoNiGe)$_{x}$ alloy is initiated by orthorhombic embryos.

Phase-field simulations of the effect of temperature and interface for zirconium δ-hydrides Suggested by editors

Zi-Hang Chen(陈子航), Jie Sheng(盛杰), Yu Liu(刘瑜), Xiao-Ming Shi(施小明), Houbing Huang(黄厚兵), Ke Xu(许可), Yue-Chao Wang(王越超), Shuai Wu(武帅), Bo Sun(孙博), Hai-Feng Liu(刘海风), and Hai-Feng Song(宋海峰)

Chin. Phys. B, 2024, 33 (4): 048201. DOI: 10.1088/1674-1056/ad1f4d

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Hydride precipitation in zirconium cladding materials can damage their integrity and durability. Service temperature and material defects have a significant effect on the dynamic growth of hydrides. In this study, we have developed a phase-field model based on the assumption of elastic behaviour within a specific temperature range (613 K—653 K). This model allows us to study the influence of temperature and interfacial effects on the morphology, stress, and average growth rate of zirconium hydride. The results suggest that changes in temperature and interfacial energy influence the length-to-thickness ratio and average growth rate of the hydride morphology. The ultimate determinant of hydride orientation is the loss of interfacial coherency, primarily induced by interfacial dislocation defects and quantifiable by the mismatch degree q. An escalation in interfacial coherency loss leads to a transition of hydride growth from horizontal to vertical, accompanied by the onset of redirection behaviour. Interestingly, redirection occurs at a critical mismatch level, denoted as q_c, and remains unaffected by variations in temperature and interfacial energy. However, this redirection leads to an increase in the maximum stress, which may influence the direction of hydride crack propagation. This research highlights the importance of interfacial coherency and provides valuable insights into the morphology and growth kinetics of hydrides in zirconium alloys.

Interfacial DMI in Fe/Pt thin films grown on different buffer layers

Wen-Jun Zhang(张文君), Fei Wei(魏菲), Bing Liu(刘冰), Yang Zhou(周阳), Shi-Shou Kang(康仕寿), and Bing Sun(孙兵)

Chin. Phys. B, 2024, 33 (4): 048501. DOI: 10.1088/1674-1056/ad1b41

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We study the interfacial Dzyaloshinskii—Moriya interactions (i-DMI) of Fe/Pt bilayers grown on Si substrates with MgO, SiO₂, or Ta each as a buffer layer on the basis of wave-vector-resolved Brillouin light scattering (BLS) measurement. The obtained i-DMI energy values for Fe/Pt on MgO, Ta, and SiO₂ buffer layers are 0.359, 0.321, and 0.274 mJ/m², respectively. The large i-DMI value observed in Fe/Pt system on the MgO buffer layer can be attributed to the good interfacial quality and the Rshaba effect at the MgO/Fe interface. Moreover, the MgO/Fe/Pt system, benefiting from better sample quality, exhibits a lower damping factor. Furthermore, layer-resolved first-principles calculations are carried out to gain a more in-depth understanding of the origin of the i-DMI in the Fe/Pt system. The results indicate that in the Fe(110)/Pt(111) system, the substantial DMI energy between Fe spins at the interface is related to a significant change in spin—orbit coupling (SOC) energy in the neighboring Pt layer. In contrast, for the MgO(002)/Fe(002) system, both the DMI and its related SOC energy are concentrated at the interfacial Fe layer. Our investigation will provide a valuable insight into the spintronic community in exploring novel devices with chirality dependence.

High-resolution imaging of magnetic fields of banknote anti-counterfeiting strip using fiber diamond probe Suggested by editors

Xu-Tong Zhao(赵旭彤), Fei-Yue He(何飞越), Ya-Wen Xue(薛雅文), Wen-Hao Ma(马文豪), Xiao-Han Yin(殷筱晗), Sheng-Kai Xia(夏圣开), Ming-Jing Zeng(曾明菁), and Guan-Xiang Du(杜关祥)

Chin. Phys. B, 2024, 33 (4): 048502. DOI: 10.1088/1674-1056/ad1b44

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Counterfeiting of modern banknotes poses a significant challenge, prompting the use of various preventive measures. One such measure is the magnetic anti-counterfeiting strip. However, due to its inherent weak magnetic properties, visualizing its magnetic distribution has been a longstanding challenge. In this work, we introduce an innovative method by using a fiber optic diamond probe, a highly sensitive quantum sensor designed specifically for detecting extremely weak magnetic fields. We employ this probe to achieve high-resolution imaging of the magnetic fields associated with the RMB 50 denomination anti-counterfeiting strip. Additionally, we conduct computer simulations by using COMSOL Multiphysics software to deduce the potential geometric characteristics and material composition of the magnetic region within the anti-counterfeiting strip. The findings and method presented in this study hold broader significance, extending the RMB 50 denomination to various denominations of the Chinese currency and other items that employ magnetic anti-counterfeiting strips. These advances have the potential to significantly improve and promote security measures in order to prevent the banknotes from being counterfeited.

Dynamical behaviors in discrete memristor-coupled small-world neuronal networks

Jieyu Lu(鲁婕妤), Xiaohua Xie(谢小华), Yaping Lu(卢亚平), Yalian Wu(吴亚联), Chunlai Li(李春来), and Minglin Ma(马铭磷)

Chin. Phys. B, 2024, 33 (4): 048701. DOI: 10.1088/1674-1056/ad1483

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The brain is a complex network system in which a large number of neurons are widely connected to each other and transmit signals to each other. The memory characteristic of memristors makes them suitable for simulating neuronal synapses with plasticity. In this paper, a memristor is used to simulate a synapse, a discrete small-world neuronal network is constructed based on Rulkov neurons and its dynamical behavior is explored. We explore the influence of system parameters on the dynamical behaviors of the discrete small-world network, and the system shows a variety of firing patterns such as spiking firing and triangular burst firing when the neuronal parameter α is changed. The results of a numerical simulation based on Matlab show that the network topology can affect the synchronous firing behavior of the neuronal network, and the higher the reconnection probability and number of the nearest neurons, the more significant the synchronization state of the neurons. In addition, by increasing the coupling strength of memristor synapses, synchronization performance is promoted. The results of this paper can boost research into complex neuronal networks coupled with memristor synapses and further promote the development of neuroscience.

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