Chin. Phys. B

Editorial: Stephen J. Pennycook—A research life in atomic-resolution STEM and EELS Suggested by editors

Hong-Jun Gao(高鸿钧), Wu Zhou(周武), and Ryo Ishikawa

Chin. Phys. B, 2024, 33 (12): 120102. DOI: 10.1088/1674-1056/ad9e9f

Abstract ( 1 )

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Combining electron microscopy with atomic-scale calculations—A personal perspective Suggested by editors

Sokrates T. Pantelides

Chin. Phys. B, 2024, 33 (12): 120704. DOI: 10.1088/1674-1056/ad8ece

Abstract ( 35 )

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I had the privilege and the pleasure to work closely with Stephen J. Pennycook for about twenty years, having a group of post-docs and Vanderbilt-University graduate students embedded in his electron microscopy group at Oak Ridge National Laboratory, spending on average a day per week there. We combined atomic-resolution imaging of materials, electron-energy-loss spectroscopy, and density-functional-theory calculations to explore and elucidate diverse materials phenomena, often resolving long-standing issues. This paper is a personal perspective of that journey, highlighting a few examples to illustrate the power of combining theory and microscopy and closing with an assessment of future prospects.

A universal resist-assisted metal transfer method for 2D semiconductor contacts Suggested by editors

Xuanye Liu(刘轩冶), Linxuan Li(李林璇), Chijun Wei(尉驰俊), Peng Song(宋鹏), Hui Gao(高辉), Kang Wu(吴康), Nuertai Jiazila(努尔泰cdot加孜拉), Jiequn Sun(孙杰群), Hui Guo(郭辉), Haitao Yang(杨海涛), Wu Zhou(周武), Lihong Bao(鲍丽宏), and Hong-Jun Gao(高鸿钧)

Chin. Phys. B, 2024, 33 (12): 127302. DOI: 10.1088/1674-1056/ad8db4

Abstract ( 38 )

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With the explosive exploration of two-dimensional (2D) semiconductors for device applications, ensuring effective electrical contacts has become critical for optimizing device performance. Here, we demonstrate a universal resist-assisted metal transfer method for creating nearly free-standing metal electrodes on the SiO$_{2}$/Si substrate, which can be easily transferred onto 2D semiconductors to form van der Waals (vdW) contacts. In this method, polymethyl methacrylate (PMMA) serves both as an electron resist for electrode patterning and as a sacrificial layer. Contacted with our transferred electrodes, MoS$_{2}$ exhibits tunable Schottky barrier heights and a transition from n-type dominated to ambipolar conduction with increasing metal work functions, while InSe shows pronounced ambipolarity. Additionally, using $\alpha$-In$_{2}$Se$_{3}$ as an example, we demonstrate that our transferred electrodes enhance resistance switching in ferroelectric memristors. Finally, the universality of our method is evidenced by the successful transfer of various metals with different adhesion forces and complex patterns.

Pressure-induced structural transitions and metallization in ZrSe₂ Suggested by editors

Yiping Gao(高一平), Chenchen Liu(刘晨晨), Can Tian(田灿), Chengcheng Zhu(朱程程), Xiaoli Huang(黄晓丽), and Tian Cui(崔田)

Chin. Phys. B, 2024, 33 (12): 126104. DOI: 10.1088/1674-1056/ad8ec9

Abstract ( 39 )

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High-pressure studies of two-dimensional materials have revealed numerous novel properties and physical mechanisms behind them. As a typical material of transition metal dichalcogenides (TMDs), ZrSe$_{2}$ exhibits high carrier mobility, rich electronic states regulated by doping, and high potential in applications at ambient pressure. However, the properties of ZrSe$_{2}$ under pressure are still not clear, especially for the structural and electrical properties. Here, we report the investigation of ZrSe$_{2}$ under pressure up to 66.5 GPa by in-situ x-ray diffraction, Raman, electrical transport measurements, and first-principles calculations. Two structural phase transitions occur in ZrSe$_{2}$ at 8.3 GPa and 31.5 GPa, from $P$-3$m$1 symmetry to $P$2$_{1}$/$m$ symmetry, and finally transformed into a non-layer $I$4/mmm symmetry structure. Pressure-induced metallic transition is observed at around 19.4 GPa in phase II which aligns well with the results of the calculation. Our work will help to improve the understanding of the evolution of the structure and electrical transport properties of two-dimensional materials.

Pressure-induced superconductivity and phase transition in PbSe and PbTe Suggested by editors

Yuyang Jiang(江宇阳), Cuiying Pei(裴翠颖), Qi Wang(王琦), Juefei Wu(吴珏霏), Lili Zhang(张丽丽), Chao Xiong(熊超), and Yanpeng Qi(齐彦鹏)

Chin. Phys. B, 2024, 33 (12): 126105. DOI: 10.1088/1674-1056/ad8ecc

Abstract ( 42 )

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The IV-VI semiconducting chalcogenides are a large material family with distinct physical behavior. Here, we systematically investigate the effect of pressure on the electronic and crystal structures of PbSe and PbTe by combining high-pressure electrical transport and synchrotron x-ray diffraction (XRD) measurements. The resistivity of PbSe and PbTe changes dramatically under high pressure and a non-monotonic evolution of $\rho (T)$ is observed. Both PbSe and PbTe are found to undergo semiconductor-metal transition upon compression and show superconductivity under higher pressure. The structural evolutions from the Fm$\bar{3}m$ to Pnma phase and then to the Pm$\bar{3}m$ phase in PbSe are verified by the x-ray diffraction. The present findings reveal the internal correlation between the structural evolution and the physical properties in lead chalcogenides.

Design of superconducting compounds at lower pressure via intercalating XH₄ molecules (X= B, C, and N) into fcc lattices Suggested by editors

Yue Zhao(赵玥), Sihan Liu(刘思涵), Jiao Liu(刘骄), Tingting Gu(顾婷婷), Jian Hao(郝健), Jingming Shi(石景明), Wenwen Cui(崔文文), and Yinwei Li(李印威)

Chin. Phys. B, 2024, 33 (12): 127101. DOI: 10.1088/1674-1056/ad7c31

Abstract ( 42 )

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Recently, many encouraging experimental advances have been achieved in ternary hydrides superconductors under high pressure. However, the extreme pressure required is indeed a challenge for practical application, which promotes a further exploration for high temperature ($T_{\rm c}$) superconductors at relatively low pressure. Herein, we performed a systematic theoretical investigation on a series of ternary hydrides with stoichiometry $AX_2$H$_8$, which is constructed by interacting molecular $X$H$_4$ ($X=$ B, C, and N) into the fcc metal $A$ lattice under low pressure of 0-150 GPa. We uncovered five compounds which are dynamically stable below 100 GPa, e.g., AcB$_2$H$_8$ (25 GPa), LaB$_2$H$_8$ (40 GPa), RbC$_2$H$_8$ (40 GPa), CsC$_2$H$_8$ (60 GPa), and SrC$_2$H$_8$ (65 GPa). Among them, AcB$_2$H$_8$, which is energetically stable above 2.5 GPa, exhibits the highest $T_{\rm c}$ of 32 K at 25 GPa. The superconductivity originates mainly from the coupling between the electron of Ac atoms and the associated low-frequency phonons, distinct from the previous typical hydrides with H-derived superconductivity. Our results shed light on the future exploration of superconductivity among ternary compounds at low pressure.

A nanosecond level current pulse capture taper optical fiber probe based on micron level nitrogen-vacancy color center diamond Suggested by editors

Yuchen Bian(卞雨辰), Yangfan Mao(毛扬帆), Honghao Chen(陈鸿浩), Shiyu Ge(葛仕宇), Wentao Lu(卢文韬), Chengkun Wang(王成坤), Sihan An(安思瀚), and Guanxiang Du(杜关祥)

Chin. Phys. B, 2024, 33 (12): 120301. DOI: 10.1088/1674-1056/ad78da

Abstract ( 41 )

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This work demonstrates a micron-sized nanosecond current pulse probe using a quantum diamond magnetometer. A micron-sized diamond crystal affixed to a fiber tip is integrated on the end of a conical waveguide. We demonstrate realtime visualization of a single 100 nanosecond pulse and discrimination of two pulse trains of different frequencies with a coplanar waveguide and a home-made PCB circuit. This technique finds promising applications in the display of electronic stream and can be used as a pulse discriminator to simultaneously receive and demodulate multiple pulse frequencies. This method of detecting pulse current is expected to provide further detailed analysis of the internal working state of the chip.

Automatic architecture design for distributed quantum computing Suggested by editors

Ting-Yu Luo(骆挺宇), Yu-Zhen Zheng(郑宇真), Xiang Fu(付祥), and Yu-Xin Deng(邓玉欣)

Chin. Phys. B, 2024, 33 (12): 120302. DOI: 10.1088/1674-1056/ad7c2c

Abstract ( 39 )

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In distributed quantum computing (DQC), quantum hardware design mainly focuses on providing as many as possible high-quality inter-chip connections. Meanwhile, quantum software tries its best to reduce the required number of remote quantum gates between chips. However, this “hardware first, software follows” methodology may not fully exploit the potential of DQC. Inspired by classical software-hardware co-design, this paper explores the design space of application-specific DQC architectures. More specifically, we propose AutoArch, an automated quantum chip network (QCN) structure design tool. With qubits grouping followed by a customized QCN design, AutoArch can generate a near-optimal DQC architecture suitable for target quantum algorithms. Experimental results show that the DQC architecture generated by AutoArch can outperform other general QCN architectures when executing target quantum algorithms.

Nonlinear enhanced mass sensor based on optomechanical system Suggested by editors

Xin-Xin Man(满鑫鑫), Jing Sun(孙静), Wen-Zhao Zhang(张闻钊), Lijuan Luo(罗丽娟), and Guangri Jin(金光日)

Chin. Phys. B, 2024, 33 (12): 120303. DOI: 10.1088/1674-1056/ad84cf

Abstract ( 42 )

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A high-precision and tunable mass detection scheme based on a double-oscillator optomechanical system is proposed. By designating one of the oscillators as the detection port, tiny mass signals can be probed through the frequency shift of the output spectrum, utilizing the system's optomechanically induced transparency (OMIT) effect. By solving the output of the optical mode, we demonstrate that the system exhibits two OMIT windows due to the double-oscillator coupling, with one window being strongly dependent on the mass to be detected. Characterizing the spectrum around this window enables high magnification and precise detection of the input signal under nonlinear parameter conditions. Additionally, our scheme shows resilience to environmental temperature variations and drive strength perturbations.

M²CS: A microwave measurement and control system for large-scale superconducting quantum processors Suggested by editors

Jiawei Zhang(张家蔚), Xuandong Sun(孙炫东), Zechen Guo(郭泽臣), Yuefeng Yuan(袁跃峰), Yubin Zhang(张玉斌), Ji Chu(储继), Wenhui Huang(黄文辉), Yongqi Liang(梁咏棋), Jiawei Qiu(邱嘉威), Daxiong Sun(孙大雄), Ziyu Tao(陶子予), Jiajian Zhang(张家健), Weijie Guo(郭伟杰), Ji Jiang(蒋骥), Xiayu Linpeng(林彭夏雨), Yang Liu(刘阳), Wenhui Ren(任文慧), Jingjing Niu(牛晶晶), Youpeng Zhong(钟有鹏), and Dapeng Yu(俞大鹏)

Chin. Phys. B, 2024, 33 (12): 120309. DOI: 10.1088/1674-1056/ad8a49

Abstract ( 42 )

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As superconducting quantum computing continues to advance at an unprecedented pace, there is a compelling demand for the innovation of specialized electronic instruments that act as crucial conduits between quantum processors and host computers. Here, we introduce a microwave measurement and control system (M$^{2}$CS) dedicated to large-scale superconducting quantum processors. M$^{2}$CS features a compact modular design that balances overall performance, scalability and flexibility. Electronic tests of M$^{2}$CS show key metrics comparable to commercial instruments. Benchmark tests on transmon superconducting qubits further show qubit coherence and gate fidelities comparable to state-of-the-art results, confirming M$^{2}$CS's capability to meet the stringent requirements of quantum experiments running on intermediate-scale quantum processors. The compact and scalable nature of our design holds the potential to support over 1000 qubits after upgrade in stability and integration. The M$^{2}$CS architecture may also be adopted to a wider range of scenarios, including other quantum computing platforms such as trapped ions and silicon quantum dots, as well as more traditional applications like microwave kinetic inductance detectors and phased array radar systems.

Exact quantum dynamics for two-level systems with time-dependent driving Suggested by editors

Zhi-Cheng He(贺郅程), Yi-Xuan Wu(吴奕璇), and Zheng-Yuan Xue(薛正远)

Chin. Phys. B, 2024, 33 (12): 120310. DOI: 10.1088/1674-1056/ad8a4c

Abstract ( 35 )

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It is well known that the time-dependent Schrrödinger equation can only be solved exactly in very rare cases, even for two-level quantum systems. Thus, finding the exact quantum dynamics under a time-dependent Hamiltonian is not only fundamentally important in quantum physics but also facilitates active quantum manipulations for quantum information processing. In this work, we present a method for generating nearly infinite analytically assisted solutions to the Schrödinger equation for a qubit under time-dependent driving. These analytically assisted solutions feature free parameters with only boundary restrictions, making them applicable in a variety of precise quantum manipulations. Due to the general form of the time-dependent Hamiltonian in our approach, it can be readily implemented in various experimental setups involving qubits. Consequently, our scheme offers new solutions to the Schrödinger equation, providing an alternative analytical framework for precise control over qubits.

Enhanced sensing of anharmonicities in a gain-based anti-PT symmetric system Suggested by editors

Ya-Wei Zeng(曾亚伟), Tian-Le Yang(杨天乐), Qi-Yin Lin(林琪茵), and Wan-Jun Su(苏万钧)

Chin. Phys. B, 2024, 33 (12): 124201. DOI: 10.1088/1674-1056/ad8a4d

Abstract ( 31 )

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We study the enhanced sensing of weak anharmonicities in a gain-based cavity-magnon-waveguide coupled system. By dissipatively coupling the two subsystems through a mediating waveguide, the Hamiltonian of the system is tailored to be anti-parity-time symmetric. Unique to the gain condition, the eigenvalues exhibit two singularities with linewidth suppression, distinguishing them from those of gain-free systems. Under the gain condition, a counter-intuitive bistable signature emerges even at low drive powers. As the effective gain approaches a certain value, this bistability yields a significantly enhanced spin-current response of the magnon mode. Consequently, the sensitivity, quantified by an enhancement factor, is enhanced remarkably compared to the linewidth suppression scenario. Moreover, the high enhancement factor can be sustained over a broad gain-bandwidth and also stays large even when the coherent coupling becomes considerably strong. Based on the integrated cavity-magnon-waveguide systems, this scheme can be used for sensing different physical quantities related to the Kerr-type nonlinearity and has potential applications in high-precision measuring microwave-signal nonlinearities.

Micron-resolved quantum precision measurement of magnetic field at the Tesla level Suggested by editors

Si-Han An(安思瀚), Shi-Yu Ge(葛仕宇), Wen-Tao Lu(卢文韬), Guo-Bin Chen(陈国彬), Sheng-Kai Xia(夏圣开), Ai-Qing Chen(陈爱庆), Cheng-Kun Wang(王成坤), Lin-Yan Yu(虞林嫣), Zhi-Qiang Zhang(张致强), Yang Wang(汪洋), Gui-Jin Tang(唐贵进), Hua-Fu Cheng(程华富), and Guan-Xiang Du(杜关祥)

Chin. Phys. B, 2024, 33 (12): 120305. DOI: 10.1088/1674-1056/ad7e9b

Abstract ( 52 )

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We develop a quantum precision measurement method for magnetic field at the Tesla level by utilizing a fiber diamond magnetometer. Central to our system is a micron-sized fiber diamond probe positioned on the surface of a coplanar waveguide made of nonmagnetic materials. Calibrated with a nuclear magnetic resonance magnetometer, this probe demonstrates a broad magnetic field range from 10 mT to 1.5 T with a nonlinear error better than 0.0028% under a standard magnetic field generator and stability better than 0.0012% at a 1.5 T magnetic field. Finally, we demonstrate quantitative mapping of the vector magnetic field on the surface of a permanent magnet using the diamond magnetometer.

Apparatus for producing single strontium atoms in an optical tweezer array Suggested by editors

Kai Wen(文凯), Huijin Chen(陈辉锦), Xu Yan(颜煦), Zejian Ren(任泽剑), Chengdong He(何成东), Elnur Hajiyev, Preston Tsz Fung Wong(黄梓峰), and Gyu-Boong Jo

Chin. Phys. B, 2024, 33 (12): 120703. DOI: 10.1088/1674-1056/ad84d0

Abstract ( 33 )

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We outline an experimental setup for efficiently preparing a tweezer array of $^{88}$Sr atoms. Our setup uses permanent magnets to maintain a steady-state two-dimensional magneto-optical trap (MOT) which results in a loading rate of up to $10^{8}$ s$^{-1}$ at 5 mK for the three-dimensional blue MOT. This enables us to trap $2\times10^{6}$ $^{88}$Sr atoms at 2 μK in a narrow-line red MOT with the $^{1}$S$_{0}$ $\rightarrow$ $^{3}$P$_{1}$ intercombination transition at 689 nm. With the Sisyphus cooling and pairwise loss processes, single atoms are trapped and imaged in 813 nm optical tweezers, exhibiting a lifetime of 2.5 min. We further investigate the survival fraction of a single atom in the tweezers and characterize the optical tweezer array using a release and recapture technique. Our experimental setup serves as an excellent reference for those engaged in experiments involving optical tweezer arrays, cold atom systems, and similar research.

Influence of crystal dimension on performance of spherical crystal self-emission imager Suggested by editors

Chenglong Zhang(张成龙), Yihang Zhang(张翌航), Haochen Gu(谷昊琛), Nuo Chen(陈诺), Xiaohui Yuan(远晓辉), Zhe Zhang(张喆), Miaohua Xu(徐妙华), Yutong Li(李玉同), Yingjun Li(李英骏), and Jie Zhang(张杰)

Chin. Phys. B, 2024, 33 (12): 125205. DOI: 10.1088/1674-1056/ad84d2

Abstract ( 31 )

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The spherical crystal imaging system, noted for its high energy spectral resolution (monochromaticity) and spatial resolution, is extensively applied in high energy density physics and inertial confinement fusion research. This system supports studies on fast electron transport, hydrodynamic instabilities, and implosion dynamics. The x-ray source, produced through laser-plasma interaction, emits a limited number of photons within short time scales, resulting in predominantly photon-starved images. Through ray-tracing simulations, we investigated the impact of varying crystal dimensions on the performance of a spherical crystal self-emission imager. We observed that increasing the crystal dimension leads to higher imaging efficiency but at the expense of monochromaticity, causing broader spectral acceptance and reduced spatial resolution. Furthermore, we presented a theoretical model to estimate the spatial resolution of the imaging system within a specific energy spectrum range, detailing the expressions for the effective size of the crystal. The spatial resolution derived from the model closely matches the numerical simulations.

ScatterX: A software for fast processing of high-throughput small-angle scattering data Suggested by editors

Fei Xie(谢飞), Mei Xie(解梅), Baoyu Song(宋宝玉), Qiaoyu Guo(郭桥雨), and Xuechen Jiao(焦学琛)

Chin. Phys. B, 2024, 33 (12): 120101. DOI: 10.1088/1674-1056/ad8b36

Abstract ( 36 )

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Scattering experiments become increasingly popular in modern scientific research, including the areas of materials, biology, chemistry, physics, etc. Besides, various types of scattering facilities have been developed recently, such as lab-based x-ray scattering equipment, national synchrotron facilities and large neutron facilities. These above-mentioned trends bring up fast-increasing data amounts of scattering data, as well as different scattering types (x-ray, neutron, laser and even microwaves). To help researchers process and analyze scattering data more efficiently, we developed a general and model-free scattering data analysis software based on matrix operation, which has the unique advantage of high throughput scattering data processing, analysis and visualization. To maximize generality and efficiency, data processing is performed based on a three-dimensional matrix, where scattering curves are saved as matrices or vectors, rather than the traditional definition of paired values. It can not only realize image batch processing, background subtraction and correction, but also analyze data according to scattering theory and model, such as radius of gyration, fractal dimension and other physical quantities. In the aspect of visualization, the software allows the modify the color maps of two-dimensional scattering images and the gradual color variation of one-dimensional curves to suit efficient data communications. In all, this new software can work as a stand-alone platform for researchers to process, analyze and visualize scattering data from different research facilities without considering different file types or formats. All codes in this manuscript are open-sourced and can be easily implemented in matrix-based software, such as MATLAB, Python and Igor.

One-step synthesis of cubic gauche polymeric nitrogen with high yield just by heating ^Hot! Suggested by editors

Liangfei Wu(吴良飞), Yuxuan Xu(徐宇轩), Guo Chen(陈果), Junfeng Ding(丁俊峰), Ming Li(李明), Zhi Zeng(曾雉), and Xianlong Wang(王贤龙)

Chin. Phys. B, 2024, 33 (12): 126802. DOI: 10.1088/1674-1056/ad9569

Abstract ( 37 )

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A high-efficient one-step synthesis of cubic gauche polymeric nitrogen was developed just by thermal treatment of KN$_3$ powders. Raman and infrared spectra confirm the formation of cubic gauche polymeric nitrogen. Further thermogravimetric differential scanning calorimeter measurements show that the content of cubic gauche polymeric nitrogen is as high as 1.5 wt% with high thermal stability, which is the highest content value reported so far.

Disassembling one-dimensional chains in molybdenum oxides Suggested by editors

Xian Du(杜宪), Yidian Li(李义典), Wenxuan Zhao(赵文轩), Runzhe Xu(许润哲), Kaiyi Zhai(翟恺熠), Yulin Chen(陈宇林), and Lexian Yang(杨乐仙)

Chin. Phys. B, 2024, 33 (12): 127102. DOI: 10.1088/1674-1056/ad8bb2

Abstract ( 25 )

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The dimensionality of quantum materials strongly affects their physical properties. Although many emergent phenomena, such as charge-density wave and Luttinger liquid behavior, are well understood in one-dimensional (1D) systems, the generalization to explore them in higher dimensional systems is still a challenging task. In this study, we aim to bridge this gap by systematically investigating the crystal and electronic structures of molybdenum-oxide family compounds, where the contexture of 1D chains facilitates rich emergent properties. While the quasi-1D chains in these materials share general similarities, such as the motifs made up of MoO$_{{6}}$ octahedrons, they exhibit vast complexity and remarkable tunability. We disassemble the 1D chains in molybdenum oxides with different dimensions and construct effective models to excellently fit their low-energy electronic structures obtained by ab initio calculations. Furthermore, we discuss the implications of such chains on other physical properties of the materials and the practical significance of the effective models. Our work establishes the molybdenum oxides as simple and tunable model systems for studying and manipulating the dimensionality in quantum systems.

Ultrafast reconfigurable direct charge trapping devices based on few-layer MoS₂ ^Hot! Suggested by editors

Hui Gao(高辉), Xuanye Liu(刘轩冶), Peng Song(宋鹏), Chijun Wei(尉驰俊), Nuertai Jiazila(努尔泰cdot加孜拉), Jiequn Sun(孙杰群), Kang Wu(吴康), Hui Guo(郭辉), Haitao Yang(杨海涛), Lihong Bao(鲍丽宏), and Hong-Jun Gao(高鸿钧)

Chin. Phys. B, 2024, 33 (12): 127201. DOI: 10.1088/1674-1056/ad8ecd

Abstract ( 35 )

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Charge trapping devices incorporating 2D materials and high-$\kappa$ dielectrics have emerged as promising candidates for compact, multifunctional memory devices compatible with silicon-based manufacturing processes. However, traditional charge trapping devices encounter bottlenecks including complex device structure and low operation speed. Here, we demonstrate an ultrafast reconfigurable direct charge trapping device utilizing only a 30 nm-thick Al$_{2}$O$_{3}$ trapping layer with a MoS$_{2}$ channel, where charge traps reside within the Al$_{2}$O$_{3}$ bulk confirmed by transfer curves with different gate-voltage sweeping rates and photoluminescence (PL) spectra. The direct charging tapping device shows exceptional memory performance in both three-terminal and two-terminal operation modes characterized by ultrafast three-terminal operation speed ($\sim$300 ns), an extremely low OFF current of 10$^{-14}$ A, a high ON/OFF current ratio of up to 10$^{7}$, and stable retention and endurance properties. Furthermore, the device with a simple symmetrical structure exhibits $V_{\rm D}$ polarity-dependent reverse rectification behavior in the high resistance state (HRS), with a rectification ratio of 10$^{5}$. Additionally, utilizing the synergistic modulation of the conductance of the MoS$_{2}$ channel by $V_{\rm D}$ and $V_{\rm G}$, it achieves gate-tunable reverse rectifier and ternary logic capabilities.

Higher-order topological corner states and origin in monolayer LaBrO ^Hot! Suggested by editors

Qing Wang(王庆), and Ning Hao(郝宁)

Chin. Phys. B, 2024, 33 (12): 127303. DOI: 10.1088/1674-1056/ad8a50

Abstract ( 68 )

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Intrinsic higher-order topological insulators driven solely by orbital coupling are rare in electronic materials. Here, we propose that monolayer LaBrO is an intrinsic two-dimensional second-order topological insulator. The generalized second-order topological phase arises from the coupling between the 5d orbital of the La atom and the 2p orbital of the O atom. The underlying physics can be thoroughly described by a four-band generalized higher-order topological model. Notably, the edge states and corner states of monolayer LaBrO exhibit different characteristics in terms of morphology, number, and location distribution under different boundary and nanocluster configurations. Furthermore, the higher-order topological corner states of monolayer LaBrO are robust against variations in spin-orbit coupling and different values of Hubbard $U$. This provides a material platform for studying intrinsic 2D second-order topological insulators.

Spin fluctuations and orbital-selective superconductivity in Ba₂CuO_4-y: A FLEX study ^Hot! Suggested by editors

Pei-Jun Zheng(郑裴俊), Ya-Min Quan(全亚民), and Liang-Jian Zou(邹良剑)

Chin. Phys. B, 2024, 33 (12): 127401. DOI: 10.1088/1674-1056/ad8cbe

Abstract ( 40 )

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Recently discovered Ba$_2$CuO$_{4-y}$ provides new perspectives to the study of high-temperature superconductivity. Whereas, little is known about the spin dynamics of this material. In this work, we employ the fluctuation exchange (FLEX) approximation within the framework of spin-fluctuation mediated superconductivity to examine the behavior of the spin fluctuations of a two-orbital Hubbard model for Ba$_2$CuO$_{4-y}$. Our calculations reveal an extraordinary spin resonance mode coupled to the superconducting state in the hole-underdoped regime. Furthermore, we confirm that the coupling between the electrons and this resonance mode can lead to a dip-like feature in the electronic spectrum as a feedback effect. In the hole-overdoped regime, by incorporating self energy into our calculations, we obtain orbital-dependent renormalizations and show how these self-energy effects can lead to the detailed gap structures and the orbital-selective superconductivity, which could not be obtained in a previous study using random phase approximation (RPA). This research may shed new light on searching for unconventional superconductors with higher transition temperatures.

Chiral polaritons in semiconductor perovskite metasurface enhanced by bound states in the continuum ^Hot! Suggested by editors

Dun Wang(汪顿), Albert Y. Xiong, Julia Q. Zhang, Zengde She(佘增德), Xiaofeng Kang(康晓峰), Ying Zhu(朱莹), Sanjib Ghosh, and Qihua Xiong(熊启华)

Chin. Phys. B, 2024, 33 (12): 128103. DOI: 10.1088/1674-1056/ad8db5

Abstract ( 35 )

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The exploration of novel chiral optical platforms holds both fundamental and practical importances, which have shown great promise towards applications in valleytronics, chiral sensing and nanoscopic chiroptics. In this work, we combine two key concepts—chiral bound states in the continuum and exciton polaritons - to showcase a strong chiral response from polaritons. Using the finite element method, we numerically design a CsPbBr$_{3}$ based metasurface that supports intrinsically chiral bound states in the continuum and verify the chirality by calculating the reflection spectrum and eigen-polarization mapping. We further demonstrate chirality-dependent exciton polariton angular dispersion arising from the strong coupling between the chiral BIC and excitons in CsPbBr$_{3}$ by simulating the polariton angle-resolved absorption spectrum. Reciprocity analysis reveals that the polariton photoluminescence in different momentum space locations is selectively enhanced by chiral pumping light. Our results suggest a promising first step towards chiral polaritonics.

Deep-learning-assisted optical communication with discretized state space of structured light

Minyang Zhang(张敏洋), Dong-Xu Chen(陈东旭), Pengxiang Ruan(阮鹏祥), Jun Liu(刘俊), Dong-Zhi Fu(付栋之), Jun-Long Zhao(赵军龙), and Chui-Ping Yang(杨垂平)

Chin. Phys. B, 2024, 33 (12): 120304. DOI: 10.1088/1674-1056/ad8553

Abstract ( 27 )

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The rich structure of transverse spatial modes of structured light has facilitated their extensive applications in quantum information and optical communication. The Laguerre-Gaussian (LG) modes, which carry a well-defined orbital angular momentum (OAM), consist of a complete orthogonal basis describing the transverse spatial modes of light. The application of OAM in free-space optical communication is restricted due to the experimentally limited OAM numbers and the complex OAM recognition methods. Here, we present a novel method that uses the advanced deep learning technique for LG modes recognition. By discretizing the spatial modes of structured light, we turn the OAM state regression into classification. A proof-of-principle experiment is also performed, showing that our method effectively categorizes OAM states with small training samples and the accuracy exceeds 99% from three-dimensional (3D) to fifteen-dimensional (15D) space. By assigning each category a classical information, we further apply our approach to an image transmission task, achieving a transmission accuracy of 99.58%, which demonstrates the ability to encode large data with low OAM number. This work opens up a new avenue for achieving high-capacity optical communication with low OAM number based on structured light.

Vortex clusters and their active control in a cold Rydberg atomic system with PT-symmetric Bessel potential

Zhuo Fan(范灼), Yi Shi(石逸), Hang Wang(王航), Yuan Zhao(赵元), Wei Peng(彭微), and Siliu Xu(徐四六)

Chin. Phys. B, 2024, 33 (12): 120306. DOI: 10.1088/1674-1056/ad8073

Abstract ( 30 )

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We propose an approach for generating robust two-dimensional (2D) vortex clusters (VCs) in a Rydberg atomic system by utilizing parity-time ($\mathcal{PT}$) symmetric optical Bessel potential. We show that the system supports novel multi-core VCs with four and eight cores, corresponding to topological charges 2 and 4, respectively. The stability of these VCs can be dynamically adjusted through the manipulation of the gain-loss component, Kerr nonlinearities, and the degree of nonlocality inherent in the Rydberg atoms. These VCs are confined within the first lattice well of the Bessel potential, and both the power and width of lights undergo a quasi-periodic breathing phenomenon, which is attributed to the power exchange between the light fields and Bessel potential. Both self-attractive and self-repulsive Kerr interactions can sustain robust VCs within this system. The insights presented here not only facilitate the creation and manipulation of 2D VCs through $\mathcal{PT}$-symmetric potentials but also pave the way for potential applications in optical information processing and transmission.

Quantum state estimation based on deep learning

Haowen Xiao(肖皓文) and Zhiguang Han(韩枝光)

Chin. Phys. B, 2024, 33 (12): 120307. DOI: 10.1088/1674-1056/ad78d7

Abstract ( 48 )

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We used deep learning techniques to construct various models for reconstructing quantum states from a given set of coincidence measurements. Through simulations, we have demonstrated that our approach generates functionally equivalent reconstructed states for a wide range of pure and mixed input states. Compared with traditional methods, our system offers the advantage of faster speed. Additionally, by training our system with measurement results containing simulated noise sources, the system shows a significant improvement in average fidelity compared with typical reconstruction methods. We also found that constraining the variational manifold to physical states, i.e., positive semi-definite density matrices, greatly enhances the quality of the reconstructed states in the presence of experimental imperfections and noise. Finally, we validated the correctness and superiority of our model by using data generated on IBM Quantum Platform, a real quantum computer.

Tunable phonon-photon coupling induces double magnomechanically induced transparency and enhances slow light in an atom-opto-magnomechanical system

M'bark Amghar, Noura Chabar, and Mohamed Amazioug

Chin. Phys. B, 2024, 33 (12): 120308. DOI: 10.1088/1674-1056/ad8cbb

Abstract ( 37 )

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We theoretically investigate the magnomechanically induced transparency phenomenon, Fano resonance and the slow-fast light effect in the situation where an atomic ensemble is placed inside the hybrid cavity of an opto-magnomechanical system. The system is driven by dual optical and phononic drives. We show double magnomechanically induced transparency in the probe output spectrum by exploiting the phonon-photon coupling strength. Then, we study the effects of the decay rate of the cavity and the atomic ensemble on magnomechanically induced transparency. In addition, we demonstrate that effective detuning of the cavity field frequency changes the transparency window from a symmetrical to an asymmetrical profile, resembling Fano resonances. Further, the fast and slow light effects in the system are explored. We show that the slow light profile is enhanced by adjusting the phonon-photon coupling strength. This result may have potential applications in quantum information processing and communication.

Experimental test of an extension of the Rosenzweig-Porter model to mixed integrable-chaotic systems experiencing time-reversal invariance violation Suggested by editors

Xiaodong Zhang(张晓东), Jiongning Che(车炯宁), and Barbara Dietz

Chin. Phys. B, 2024, 33 (12): 120501. DOI: 10.1088/1674-1056/ad8a4e

Abstract ( 28 )

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We report on the theoretical and experimental investigations of the transition of a typical quantum system with mixed regular-integrable classical dynamics to one with violated time-reversal (${\mathcal T}$) invariance. The measurements are performed with a flat superconducting microwave resonator with circular shape in which chaoticity is induced by using either long antennas or inserting two circular disks into the cavity, and by magnetizing a ferrite disk placed at its center, which leads to violation of ${\mathcal T}$ invariance. We propose an extension of the Rosenzweig-Porter (RP) model, which interpolates between mixed regular-chaotic instead of integrable dynamics and fully chaotic dynamics with violated ${\mathcal T}$-invariance, and derive a Wigner-surmise like analytical expression for the corresponding nearest-neighbor spacing distribution. We propose a procedure involving this result and those for the RP model to determine the size of ${\mathcal T}$-invariance violation and chaoticity and validate it employing the experimental eigenfrequency spectra.

Coexisting and multiple scroll attractors in a Hopfield neural network with a controlled memristor

Qing-Qing Ma(马青青), An-Jiang Lu(陆安江), and Zhi Huang(黄智)

Chin. Phys. B, 2024, 33 (12): 120502. DOI: 10.1088/1674-1056/ad8148

Abstract ( 38 )

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A method of generating multi-double scroll attractors is proposed based on the memristor Hopfield neural network (HNN) under pulse control. First, the original hyperbolic-type memristor is added to the neural network mathematical model, and the influence of this memristor on the dynamic behavior of the new HNN is analyzed. The numerical results show that after adding the memristor, the abundant dynamic behaviors such as chaos coexistence, period coexistence and chaos period coexistence can be observed when the initial value of the system is changed. Then the logic pulse is added to the external memristor. It is found that the equilibrium point of the HNN can multiply and generate multi-double scroll attractors after the pulse stimulation. When the number of logical pulses is changed, the number of multi-double scroll attractors will also change, so that the pulse can control the generation of multi-double scroll attractors. Finally, the HNN circuit under pulsed stimulation was realized by circuit simulation, and the results verified the correctness of the numerical results.

A fractional-order chaotic Lorenz-based chemical system: Dynamic investigation, complexity analysis, chaos synchronization, and its application to secure communication

Haneche Nabil and Hamaizia Tayeb

Chin. Phys. B, 2024, 33 (12): 120503. DOI: 10.1088/1674-1056/ad7fcf

Abstract ( 42 )

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Synchronization of fractional-order chaotic systems is receiving significant attention in the literature due to its applications in a variety of fields, including cryptography, optics, and secure communications. In this paper, a three-dimensional fractional-order chaotic Lorenz model of chemical reactions is discussed. Some basic dynamical properties, such as stability of equilibria, Lyapunov exponents, bifurcation diagrams, Poincaré map, and sensitivity to initial conditions, are studied. By adopting the Adomian decomposition algorithm (ADM), the numerical solution of the fractional-order system is obtained. It is found that the lowest derivative order in which the proposed system exhibits chaos is $q=0.694$ by applying ADM. The result has been validated by the existence of one positive Lyapunov exponent and by employing some phase diagrams. In addition, the richer dynamics of the system are confirmed by using powerful tools in nonlinear dynamic analysis, such as the 0-1 test and $C_{0}$ complexity. Moreover, modified projective synchronization has been implemented based on the stability theory of fractional-order systems. This paper presents the application of the modified projective synchronization in secure communication, where the information signal can be transmitted and recovered successfully through the channel. MATLAB simulations are provided to show the validity of the constructed secure communication scheme.

Suppression of the vapor cell temperature error in a spin-exchange relaxation-free comagnetometer

Jia-Li Liu(刘佳丽), Li-Wei Jiang(姜丽伟), Chi Fang(方驰), Xin Zhao(赵鑫), and Yuan-Qiang Chen(陈远强)

Chin. Phys. B, 2024, 33 (12): 120701. DOI: 10.1088/1674-1056/ad84ce

Abstract ( 25 )

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The fluctuation of the vapor cell temperature leads to the variations of the density of the alkali metal atoms, which seriously damages the long-term stability of the spin-exchange relaxation-free (SERF) comagnetometer. To address this problem, we propose a novel method for suppressing the cell temperature error by manipulating the probe laser frequency. A temperature coefficient model of the SERF comagnetometer is established based on the steady-state response, which indicates that the comagnetometer can be tuned to a working point where the output signal is insensitive to the cell temperature fluctuation, and the working point is determined by the relaxation rate of the alkali metal atoms. The method is verified in a K-Rb-²¹Ne comagnetometer, and the experimental results are consistent with the theory. The theory and method presented here lay a foundation for the practical applications of the SERF comagnetometer.

Realization of an optimized cylindrical uniform magnetic field coil via flexible printed circuit technology

A-Hui Zhao(赵阿慧), Yong-Le Zhang(张永乐), Yue-Yue Liang(梁跃跃), Yi Zhang(张艺), Jun-Jun Zha(查君君), Dao-Rong Rui(芮道荣), Xiao-Qiang Zhang(张肖强), and Kang Yang(杨康)

Chin. Phys. B, 2024, 33 (12): 120702. DOI: 10.1088/1674-1056/ad84c1

Abstract ( 25 )

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The design and fabrication method of magnetic field coils with high uniformity is essential for atomic magnetometers. In this paper, a novel design strategy for cylindrical uniform coils is first proposed, which combines the target-field method (TFM) with an optimized slime mold algorithm (SMA) to determine optimal structure parameters. Then, the realization method for the designed cylindrical coil by using the flexible printed circuit (FPC) technology is presented. Compared with traditional fabrication methods, this method has advantages in excellent flexibility and bending property, making the coils easier to be arranged in limited space. Moreover, the manufacturing process of the FPC technology via a specific cylindrical uniform magnetic field coil is discussed in detail, and the successfully realized coil is well tested in a verification system. By comparing the uniformity performance of the experimental coil with the simulation one, the effectiveness of the FPC technology in producing cylindrical coils has been well validated.

Electron correlation in two-electron atoms: A Bohmian analysis of high-order harmonic generation in high-frequency domain Suggested by editors

Yang Song(宋阳), Shu Han(韩姝), Yujun Yang(杨玉军), and Fuming Guo(郭福明)

Chin. Phys. B, 2024, 33 (12): 123201. DOI: 10.1088/1674-1056/ad84d1

Abstract ( 29 )

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In studying interactions between intense laser fields and atoms or molecules, the role of electron correlation effects on the dynamical response is an important and pressing issue to address. Utilizing Bohmian mechanics (BM), we have theoretically explored the two-electron correlation characteristics while generating high-order harmonics in xenon atoms subjected to intense laser fields. We initially employed Bohmian trajectories to reproduce the dynamics of the electrons and subsequently utilized time-frequency analysis spectra to ascertain the emission time windows for high-order harmonics. Within these time windows, we classified the nuclear region Bohmian trajectories and observed that intense high-order harmonics are solely generated when paired Bohmian particles (BPs) concurrently appear in the nuclear region and reside there for a duration within a re-collision time window. Furthermore, our analysis of characteristic trajectories producing high-order harmonics led us to propose a two-electron re-collision model to elucidate this phenomenon. The study demonstrates that intense high-order harmonics are only generated when both electrons are in the ground state within the re-collision time window. This work discusses the implications of correlation effects between two electrons and offers valuable insights for studying correlation in multi-electron high-order harmonic generation.

Momentum distributions of symmetric (H₂⁺) and asymmetric (HeH²⁺) molecular ions in a circularly polarized laser field under different ionization mechanisms

Xin-Yu Hao(郝欣宇), Shu-Juan Yan(闫淑娟), Ying Guo(郭颖), and Jing Guo(郭静)

Chin. Phys. B, 2024, 33 (12): 123401. DOI: 10.1088/1674-1056/ad7c2b

Abstract ( 36 )

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By numerically solving the two-dimensional (2D) time-dependent Schrödinger equation (TDSE), we present photoelectron momentum distributions (PMDs) and photoelectron angular distributions (PADs) of symmetric (${{\rm H}_{2}^{+}}$) and asymmetric (${{\rm HeH}^{2+}}$) molecular ions in circularly polarized (CP) laser pulses. By adjusting the laser wavelength, two circumstances of resonance excitation and direct ionization were considered. The ionization mechanism of the resonance excitation was mainly investigated. The results show that the PMDs of ${{\rm H}_{2}^{+}}$ and ${{\rm HeH}^{2+}}$ in the $y$-direction gradually increase with increasing intensity, and the number of PMDs lobes is in good agreement with the results predicted by the ultrafast ionization model. In the resonance excitation scenario, the PMDs of ${{\rm H}_{2}^{+}}$ are dominated by two-photon ionization, whereas the PMDs of HeH$^{2+}$ are dominated by three-photon ionization. Furthermore, the PMDs of ${{\rm HeH}^{2+}}$ are stronger in the resonance excitation scenario than those of ${{\rm H}_{2}^{+}}$, which can be explained by the time-dependent population of electrons. In addition, the molecular structure is clearly imprinted onto the PMDs.

Determining the tilt of the Raman laser beam using an optical method for atom gravimeters Suggested by editors

Hua-Qing Luo(骆华清), Yao-Yao Xu(徐耀耀), Jia-Feng Cui(崔嘉丰), Xiao-Bing Deng(邓小兵), Min-Kang Zhou(周敏康), Xiao-Chun Duan(段小春), and Zhong-Kun Hu(胡忠坤)

Chin. Phys. B, 2024, 33 (12): 123701. DOI: 10.1088/1674-1056/ad7b00

Abstract ( 44 )

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The tilt of a Raman laser beam is a major systematic error in precision gravity measurement using atom interferometry. The conventional approach to evaluating this tilt error involves modulating the direction of the Raman laser beam and conducting time-consuming gravity measurements to identify the error minimum. In this work, we demonstrate a method to expediently determine the tilt of the Raman laser beam by transforming the tilt angle measurement into characterization of parallelism, which integrates the optical method of aligning the laser direction, commonly used in freely falling corner-cube gravimeters, into an atom gravimeter. A position-sensing detector (PSD) is utilized to quantitatively characterize the parallelism between the test beam and the reference beam, thus measuring the tilt precisely and rapidly. After carefully positioning the PSD and calibrating the relationship between the distance measured by the PSD and the tilt angle measured by the tiltmeter, we achieved a statistical uncertainty of less than 30 μrad in the tilt measurement. Furthermore, we compared the results obtained through this optical method with those from the conventional tilt modulation method for gravity measurement. The comparison validates that our optical method can achieve tilt determination with an accuracy level of better than 200 μrad, corresponding to a systematic error of 20 μGal in $g$ measurement. This work has practical implications for real-world applications of atom gravimeters.

Optical image watermarking based on orbital angular momentum holography

Jialong Zhu(朱家龙), Jiaying Ji(季佳滢), Le Wang(王乐), and Shengmei Zhao(赵生妹)

Chin. Phys. B, 2024, 33 (12): 124202. DOI: 10.1088/1674-1056/ad8cbd

Abstract ( 35 )

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We propose an optical image watermarking scheme based on orbital angular momentum (OAM) holography. Multiple topological charges (TCs, $l$) of OAM, as multiple cryptographic sub-keys, are embedded into the host image along with the watermark information. Moreover, the Arnold transformation is employed to further enhance the security and the scrambling time ($m$) is also served as another cryptographic key. The watermark image is embedded into the host image by using the discrete wavelet transformation (DWT) and singular value decomposition (SVD) methods. Importantly, the interference image is utilized to further enhance security. The imperceptibility of our proposed method is analyzed by using the peak signal-to-noise ratio (PSNR) and the histogram of the watermarked host image. To demonstrate robustness, a series of attack tests, including Gaussian noise, Poisson noise, salt-and-pepper noise, JPEG compression, Gaussian low-pass filtering, cropping, and rotation, are conducted. The experimental results show that our proposed method has advanced security, imperceptibility, and robustness, making it a promising option for optical image watermarking applications.

Bright soliton dynamics for resonant nonlinear Schrödinger equation with generalized cubic-quintic nonlinearity Suggested by editors

Keyu Bao(鲍柯宇), Xiaogang Tang(唐晓刚), and Ying Wang(王颖)

Chin. Phys. B, 2024, 33 (12): 124203. DOI: 10.1088/1674-1056/ad71b4

Abstract ( 23 )

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For systems modeled by the resonant nonlinear Schrödinger equation (RNLSE) with generalized cubic-quintic nonlinearity, we derive the bright soliton solution of the equation in (1+1) dimensions, using the modified $F$-expansion method along with the novel ansatz of $F$-base function. Furthermore, we extend the analytical study of soliton dynamics to higher (2+1) and (3+1) dimensions by using the self-similar method, and demonstrate the soliton behavior via graphical illustration. Moreover, we investigate the effect of the resonance term on bright soliton solution in (1+1) dimensions. Additionally, we consider the nonlinear equation models with perturbation terms and derive the bright soliton solutions for the one-dimensional (1D) to three-dimensional (3D) cases. The theoretical results derived can be used to guide the experimental studies and observations of bright solitons in systems described by RNLSE model.

Analysis and measurement of vibration characteristics of a hollowing defect based on a laser self-mixing interferometer

Yu-Xin Chen(陈煜昕), Jin-Bo Chen(陈金波), Peng Cao(曹鹏), You-Guang Zhao(赵有光), Jun Wang(王钧), Xu-Wei Teng(滕旭玮), and Chi Wang(王驰)

Chin. Phys. B, 2024, 33 (12): 124301. DOI: 10.1088/1674-1056/ad7e99

Abstract ( 36 )

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To solve the problems with the existing methods for detecting hollowing defects, such as inconvenient operation, low efficiency and intense subjectivity, and to improve the efficiency of the acoustic-optic fusion method for detecting hollowing defects, in this paper the vibration characteristics of hollowing defects are measured and analyzed using a laser self-mixing interferometer. The ceramic tile above the hollowing defect is equivalent to a thin circular plate with peripheral fixed support. According to Kirchhoff's classical circular plate theory and the circular plate displacement function based on the improved Fourier series, a theoretical model of a circular plate is established. By solving the characteristic equation, the theoretical modal parameters of hollowing defects are obtained. Subsequently, an experimental system based on a laser self-mixing interferometer is built, and modal experiments are carried out using the hammering method. The experimental modal parameters are obtained with a professional modal analysis software. Through comparative analysis between the theoretical and experimental modal parameters, the error of the natural frequency results is found to be tiny and the mode shapes are consistent. These results provide theoretical guidance for a practical non-destructive acoustic-optic fusion method for detecting hollowing defects.

Capture behavior of self-propelled particles into a hexatic ordering obstacle Suggested by editors

Jing-Yi Li(李静怡), Jin-Lei Shi(石金蕾), Ying-Ying Wang(王英英), Jun-Xing Pan(潘俊星), and Jin-Jun Zhang(张进军)

Chin. Phys. B, 2024, 33 (12): 124501. DOI: 10.1088/1674-1056/ad84c6

Abstract ( 40 )

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Computer simulations are utilized to investigate the dynamic behavior of self-propelled particles (SPPs) within a complex obstacle environment. The findings reveal that SPPs exhibit three distinct aggregation states within the obstacle, each contingent on specific conditions. A phase diagram outlining the aggregation states concerning self-propulsion conditions is presented. The results illustrate a transition of SPPs from a dispersion state to a transition state as persistence time increases within the obstacle. Conversely, as the driving strength increases, self-propelled particles shift towards a cluster state. A systematic exploration of the interplay between driving strength, persistence time, and matching degree on the dynamic behavior of self-propelled particles is conducted. Furthermore, an analysis is performed on the spatial distribution of SPPs along the $y$-axis, capture rate, maximum capture probability, and mean-square displacement. The insights gained from this research make valuable contributions to understanding the capture and collection of active particles.

Flow features induced by a rod-shaped microswimmer and its swimming efficiency: A two-dimensional numerical study

Siwen Li(李斯文), Yuxiang Ying(应宇翔), Tongxiao Jiang(姜童晓), and Deming Nie(聂德明)

Chin. Phys. B, 2024, 33 (12): 124701. DOI: 10.1088/1674-1056/ad84c3

Abstract ( 35 )

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The swimming performance of rod-shaped microswimmers in a channel was numerically investigated using the two-dimensional lattice Boltzmann method (LBM). We considered variable-length squirmer rods, assembled from circular squirmer models with self-propulsion mechanisms, and analyzed the effects of the Reynolds number (Re), aspect ratio ($\varepsilon$), squirmer-type factor ($\beta $) and blockage ratio ($\kappa$) on swimming efficiency ($\eta$) and power expenditure ($P$). The results show no significant difference in power expenditure between pushers (microswimmers propelled from the tail) and pullers (microswimmers propelled from the head) at the low Reynolds numbers adopted in this study. However, the swimming efficiency of pushers surpasses that of pullers. Moreover, as the degree of channel blockage increases (i.e., $\kappa $ increases), the squirmer rod consumes more energy while swimming, and its swimming efficiency also increases, which is clearly reflected when $\varepsilon \le 3$. Notably, squirmer rods with a larger aspect ratio $\varepsilon $ and a $\beta $ value approaching 0 can achieve high swimming efficiency with lower power expenditure. The advantages of self-propelled microswimmers are manifested when $\varepsilon > 4$ and $\beta = \pm 1$, where the squirmer rod consumes less energy than a passive rod driven by an external field. These findings underscore the potential for designing more efficient microswimmers by carefully considering the interactions between the microswimmer geometry, propulsion mechanism and fluid dynamic environment.

Shear rheology of confined double rings of dust particles in a dusty plasma Suggested by editors

Miao Tian(田淼), Jiaqi Li(李佳琪), Xuebo Yu(于雪波), Xue Liu(刘雪), Shaopeng Li(李绍鹏), Qing Li(李庆), Fucheng Liu(刘富成), and Yafeng He(贺亚峰)

Chin. Phys. B, 2024, 33 (12): 125201. DOI: 10.1088/1674-1056/ad8552

Abstract ( 41 )

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Shear rheology is a fundamental property of soft matter, which can be deformed. Although the shear rheology of fluids has been well studied at the macroscopic scale, understanding the microscopic processes of rheology at the single-particle level remains a challenging issue. Dusty plasma serves as an ideal platform for exploring microscopic dynamics of system at the individual particle level. Here, we study the shear rheology of confined double rings of strongly coupled dust particles in a dusty plasma. The outer ring is actively driven to rotate using laser illumination. Depending on the particle number, the inner ring may passively rotate following the outer ring at different angular speeds, resulting in shear rheology. The number of dust particles influences particle arrangement, which is characterized by the pair correlation function, bond-orientational order parameter, and triangle skewness. That further alters structural stability, significantly affecting the shear rheology.

Nonlinear ion acoustic waves in multicomponent plasmas with nonthermal electrons-positron and bipolar ions

Mai-Mai Lin(林麦麦), Chen-Guang Song(宋晨光), Fu-Yan Chen(陈富艳), and Ming-Yue Wang(王明月)

Chin. Phys. B, 2024, 33 (12): 125202. DOI: 10.1088/1674-1056/ad854f

Abstract ( 19 )

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This paper studied the propagating characteristics of (2+1)-dimensional nonlinear ion acoustic waves in a multicomponent plasma with nonthermal electrons, positrons, and bipolar ions. The dispersion relations are initially explored by using the small amplitude wave's dispersion relation. Then, the Sagdeev potential method is employed to study large amplitude ion acoustic waves. The analysis involves examining the system's phase diagram, Sagdeev potential function, and solitary wave solutions through numerical solution of an analytical process in order to investigate the propagation properties of nonlinear ion acoustic waves under various parameters. It is found that the propagation of nonlinear ion acoustic waves is subject to the influence of various physical parameters, including the ratio of number densities between the unperturbed positrons, electrons to positive ions, nonthermal parameters, the mass ratio of positive ions to negative ions, and the charge number ratio of negative ions to positive ions, the ratio of the electrons' temperature to positrons' temperature. In addition, the multicomponent plasma system has a compressive solitary waves with amplitude greater than zero or a rarefactive solitary waves with amplitude less than zero, in the meantime, compressive and rarefactive ion acoustic wave characteristics depend on the charge number ratio of negative ions to positive ions.

Suppression of the Kelvin-Helmholtz instability by coating in the double-cone ignition scheme

Yuan-Kai Xie(谢元凯), Cheng-Long Zhang(张成龙), Yi-Zhen Cheng(程翊真), and Ying-Jun Li(李英骏)

Chin. Phys. B, 2024, 33 (12): 125203. DOI: 10.1088/1674-1056/ad8551

Abstract ( 37 )

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In order to address the issue of gold mixing caused by the Kelvin-Helmholtz instability (KHI) in the double-cone ignition (DCI) scheme, we investigate the growth rate of the KHI at the bi-interface of the DCI scheme after applying a coating. This is done by solving the hydrodynamic equations for an ideal incompressible fluid using linear theory. Ultimately, it is discovered that applying a coating with a thickness slightly above h=0.5(λ+10 μm) and a density somewhat lower than that of the target layer can effectively reduce the growth rate of interfacial KHI. This work provides theoretical references for studying the bi-interface KHI in the DCI scheme.

Differences in the acoustic characteristics of DC bias alternating arcs in argon, helium, and nitrogen

Yutai Li(李雨泰), Qinghao Wen(文清皓), Yangyang Fu(付洋洋), Xiaobing Zou(邹晓兵), Handong Li(黎晗东), Zhigang Liu(刘志刚), Haiyun Luo(罗海云), Dun Qian(钱盾), Zhe Chen(陈喆), and Xinxin Wang(王新新)

Chin. Phys. B, 2024, 33 (12): 125204. DOI: 10.1088/1674-1056/ad8070

Abstract ( 23 )

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The acoustic effects of gas discharge plasma have received much attention. Previous studies have shown that cold plasma and thermal plasma have different principles of sound generation. In this paper, the differences in the acoustic characteristics of DC bias alternating arc plasma (thermal plasma) in different gas environments (argon, helium, and nitrogen) are investigated by combining experiments and simulations. Many processes in industrial machining involve this arc plasma. It was found that the acoustic characteristics of the arcs of these three gases are significantly different. The two key parameters, electrical and thermal conductivity of the gas, determine the acoustic characteristics of the arc by influencing the electric power of the arc and the heat dissipation through the anode. At the same drive current, the nitrogen arc has the largest voltage drop and the helium arc has the highest electroacoustic conversion efficiency. This results in the acoustic pressure amplitude being helium, nitrogen, and argon in descending order. The research contributes to a deeper understanding of the vocalization mechanism of arc plasma and provides theoretical guidance on gas selection for arc acoustic wave applications.

Correlation of microstructure and magnetic softness of Si-microalloying FeNiBCuSi nanocrystalline alloy revealed by nanoindentation Suggested by editors

Benjun Wang(汪本军), Wenjun Liu(刘文君), Li Liu(刘莉), Yu Wang(王玉), Yu Hang(杭宇), Xinyu Wang(王新宇), Mengen Shi(施蒙恩), Hanchen Feng(冯汉臣), Long Hou(侯龙), Chenchen Yuan(袁晨晨), Zhong Li(李忠), and Weihuo Li(李维火)

Chin. Phys. B, 2024, 33 (12): 126101. DOI: 10.1088/1674-1056/ad84c8

Abstract ( 35 )

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Compared to the commercial soft-magnetic alloys, the high saturation magnetic flux density ($B_{\rm s}$) and low coercivity ($H_{\rm c}$) of post-developed novel nanocrystalline alloys tend to realize the miniaturization and lightweight of electronic products, thus attracting great attention. In this work, we designed a new FeNiBCuSi formulation with a novel atomic ratio, and the microstructure evolution and magnetic softness were investigated. Microstructure analysis revealed that the amount of Si prompted the differential chemical fluctuations of Cu element, favoring the different nucleation and growth processes of $\alpha $-Fe nanocrystals. Furthermore, microstructural defects associated with chemical heterogeneities were unveiled using the Maxwell-Voigt model with two Kelvin units and one Maxwell unit based on creeping analysis by nanoindentation. The defect, with a long relaxation time in relaxation spectra, was more likely to induce the formation of crystal nuclei that ultimately evolved into the $\alpha$-Fe nanocrystals. As a result, Fe$_{84}$Ni$_{2}$B$_{12.5}$Cu$_{1}$Si$_{0.5}$ alloy with refined uniform nanocrystalline microstructure exhibited excellent magnetic softness, including a high $B_{\rm s}$ of 1.79 T and very low $H_{\rm c}$ of 2.8 A/m. Our finding offers new insight into the influence of activated defects associated with chemical heterogeneities on the microstructures of nanocrystalline alloy with excellent magnetic softness.

Upconversion photoluminescence of Er-doped Bi₄Ti₃O₁₂ ceramics enhanced by vacancy clusters revealed by positron annihilation spectroscopy Suggested by editors

Huiru Cheng(程慧茹), Yuhuan Li(李钰环), Ziwen Pan(潘子文), Jiandang Liu(刘建党), and Bangjiao Ye(叶邦角)

Chin. Phys. B, 2024, 33 (12): 126102. DOI: 10.1088/1674-1056/ad84ca

Abstract ( 27 )

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Doping of rare earth elements into Bi$_{4}$Ti$_{3}$O$_{12}$ can significantly enhance the upconversion photoluminescence (UCPL) properties, but its structure-property relationship is still unclear. In this work, Er-doped bismuth titanate Bi$_{4-x}$Er$_{x}$Ti$_{3}$O$_{12}$ ($x=0$, 0.1, 0.2, 0.3, 0.4, 0.5) ceramics were synthesized via solid-state reaction method. The x-ray diffraction analysis confirmed the orthorhombic crystalline structure of the Bi$_{4-x}$Er$_{x}$Ti$_{3}$O$_{12}$ ceramics without any secondary phases. Experiments and calculations of positron annihilation spectroscopy were carried out to characterize their defect structure. The comparison between the experimental and calculated lifetime revealed that vacancy clusters were the main defects in the ceramics. The increase of the intensity of the second positron lifetime component ($I_{2}$) of Bi$_{3.5}$Er$_{0.5}$Ti$_{3}$O$_{12}$ ceramics indicated the presence of a high concentration of vacancy clusters. The UCPL spectra showed the sudden enhanced UCPL performance in Bi$_{3.7}$Er$_{0.3}$Ti$_{3}$O$_{12}$ and Bi$_{3.5}$Er$_{0.5}$Ti$_{3}$O$_{12}$ ceramics, which were consistent with the variation of the second positron lifetime component ($I_{2}$). These results indicate that the enhanced UCPL properties are influenced not only by the concentrations of rare earth ions but also by the concentration of vacancy clusters present within the ceramics.

Ab initio study of phase stability, elastic anisotropy, and minimum thermal conductivity of MnB₂ in different crystal structures Suggested by editors

Xiao-Fan Wang(王小凡), Yi-Xian Wang(王乙先), Zhuo Wang(王卓), Yu-Xuan Zhang(张宇轩), and Jian-Bing Gu(顾建兵)

Chin. Phys. B, 2024, 33 (12): 126103. DOI: 10.1088/1674-1056/ad925c

Abstract ( 34 )

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The phase stability, elastic anisotropy, and minimum thermal conductivity of MnB$_{2}$ in different crystal structures have been investigated by first-principles calculations based on density functional theory. The results found that $P$6$_{3}/mmc$ (hP6-MnB$_{2})$, $P6/mmm$ (hP3-MnB$_{2})$, Pmmn (oP6-MnB$_{2})$, $R\bar{{3}}m$(hR3-MnB$_{2})$, Pnma (oP12-MnB$_{2})$, and Immm (oI18-MnB$_{2})$ all exhibit mechanical and dynamic stability under environmental conditions, and the sequence of phase stability was hP6 > hR3 > oP6 > oI18 > oP12 >hP3. In addition, Vickers hardness calculations indicated that hP6, hR3, oP6, and oI18 of MnB$_{2}$ have potential as hard materials, while hP3 and oP12 are not suitable as hard materials. Moreover, the elastic anisotropy of different MnB$_{2 }$ phases were also comprehensively investigated. It is found that the anisotropic order of bulk modulus is oP12 > hP3 > hP6 > hR3 > oI18 > oP6, while that of Young's modulus is oP12 > hR3 > hP6 > oP6 > hP3 > oI18. Furthermore, the minimum thermal conductivity of different MnB$_{2}$ phases was evaluated by means of Clarke's and Cahill's models. The results suggested that these MnB$_{2}$ diborides are all not suitable as thermal barrier coating materials.

Molecular beam epitaxial growth and physical properties of AlN/GaN superlattices with an average 50% Al composition Suggested by editors

Siqi Li(李思琦), Pengfei Shao(邵鹏飞), Xiao Liang(梁潇), Songlin Chen(陈松林), Zhenhua Li(李振华), Xujun Su(苏旭军), Tao Tao(陶涛), Zili Xie(谢自力), Bin Liu(刘斌), M. Ajmal Khan, Li Wang, T. T. Lin, Hideki Hirayama, Rong Zhang(张荣), and Ke Wang(王科)

Chin. Phys. B, 2024, 33 (12): 126801. DOI: 10.1088/1674-1056/ad84cc

Abstract ( 41 )

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We report molecular beam epitaxial growth and electrical and ultraviolet light emitting properties of (AlN)$m$/(GaN)$n$ superlattices (SLs), where $m$ and $n$ represent the numbers of monolayers. Clear satellite peaks observed in XRD 2$\theta $-$\omega $ scans and TEM images evidence the formation of clear periodicity and atomically sharp interfaces. For (AlN)$m$/(GaN)$n$ SLs with an average Al composition of 50%, we have obtained an electron density up to 4.48$\times10^{19}$ cm$^{-3}$ and a resistivity of 0.002 $\Omega\cdot$cm, and a hole density of 1.83$\times10^{18}$ cm$^{-3}$ with a resistivity of 3.722 $\Omega \cdot$cm, both at room temperature. Furthermore, the (AlN)$m$/(GaN)$n$ SLs exhibit a blue shift for their photoluminescence peaks, from 403 nm to 318 nm as GaN is reduced from $n=11$ to $n=4$ MLs, reaching the challenging UVB wavelength range. The results demonstrate that the (AlN)$m$/(GaN)$n$ SLs have the potential to enhance the conductivity and avoid the usual random alloy scattering of the high-Al-composition ternary AlGaN, making them promising functional components in both UVB emitter and AlGaN channel high electron mobility transistor applications.

Janus monolayers Fe₂SSeX₂ (X =Ga, In, and Tl): Robust nontrivial topology with high Chern number Suggested by editors

Kang Jia(贾康), Xiao-Jing Dong(董晓晶), Pei-Ji Wang(王培吉), and Chang-Wen Zhang(张昌文)

Chin. Phys. B, 2024, 33 (12): 127103. DOI: 10.1088/1674-1056/ad7c2a

Abstract ( 35 )

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High-performance quantum anomalous Hall (QAH) systems are crucial materials for exploring emerging quantum physics and magnetic topological phenomena. Inspired by layered FeSe materials with excellent superconducting properties, the Janus monolayers Fe$_{2}$SSe$X_{2}$ ($X ={\rm Ga}$, In and Tl) are built by the decoration of Ga, In and Tl atoms in monolayer Fe$_{2}$SSe. In first-principles calculations, Fe$_{2}$SSe$X_{2}$ have stable structures and prefer ferromagnetic (FM) ordering, and can be considered as Weyl semimetals without spin-orbit coupling. For out-of-plane (OOP) magnetic anisotropy, large nontrivial gaps are opened and the Fe$_{2}$SSe$X_{2}$ are predicted to be large-gap QAH insulators with a high Chern number $C = 2$, proved by two chiral edge states and Berry curvature. When the magnetization is flipped, the two chiral edge states can be simultaneously changed and $C =-2$ can be obtained, revealing the fascinating behavior of chiral spin-edge state locking. It is found that the QAH properties of Fe$_{2}$SSe$X_{2}$ are robust against strain. In particular, nontrivial topological quantum states can spontaneously appear for Fe$_{2}$SSeGa$_{2}$ and Fe$_{2}$SSeIn$_{2}$ because the orientations of the easy magnetic axis are adjusted from in-plane to OOP by the biaxial strain. Our studies provide excellent candidate systems to realize QAH properties with a high Chern number, and suggest more experimental explorations combining superconductivity and topology.

Strain-modulated antiferromagnetic Chern insulator in NiOsCl₆ monolayer

Bin Wu(武斌), Na Li(李娜), Xin-Lian Chen(陈新莲), Wei-Xiao Ji(纪维霄), Pei-Ji Wang(王培吉), Shu-Feng Zhang(张树峰), and Chang-Wen Zhang(张昌文)

Chin. Phys. B, 2024, 33 (12): 127301. DOI: 10.1088/1674-1056/ad84cb

Abstract ( 34 )

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Recently, Chern insulators in an antiferromagnetic (AFM) phase have been suggested theoretically and predicted in a few materials. However, the experimental observation of two-dimensional (2D) AFM quantum anomalous Hall effect is still a challenge to date. In this work, we propose that an AFM Chern insulator can be realized in a 2D monolayer of NiOsCl$_6$ modulated by a compressive strain. Strain modulation is accessible experimentally and used widely in predicting and tuning topological nontrivial phases. With first-principles calculations, we have investigated the structural, magnetic, and electronic properties of NiOsCl$_6$. Its stability has been confirmed through molecular dynamical simulations, elasticity constant, and phonon spectrum. It has a collinear AFM order, with opposite magnetic moments of 1.3 $\mu_{\rm B}$ on each Ni/Os atom, respectively, and the Néel temperature is estimated to be 93 K. In the absence of strain, it functions as an AFM insulator with a direct gap with spin-orbital coupling included. Compressive strain will induce a transition from a normal insulator to a Chern insulator characterized by a Chern number $C = 1$, with a band gap of about 30 meV. This transition is accompanied by a structural distortion. Remarkably, the Chern insulator phase persists within the 3%-10% compressive strain range, offering an alternative platform for the utilization of AFM materials in spintronic devices.

Tuning the magnetocaloric and structural properties of La_0.67Sr_0.28Pr_0.05Mn_1-xCo_xO₃ refrigeration materials

Changji Xu(徐长吉), Xinyu Jiang(姜心雨), Zhengguang Zou(邹正光), Zhuojia Xie(谢卓家), Weijian Zhang(张伟建), and Min Feng(冯敏)

Chin. Phys. B, 2024, 33 (12): 127501. DOI: 10.1088/1674-1056/ad8550

Abstract ( 37 )

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The structural, magnetic and magnetocaloric properties of perovskite manganites La$_{0.67}$Sr$_{0.28}$Pr$_{0.05}$Mn$_{1-x}$Co$_{x}$O$_{3}$ ($x = 0.05$, 0.075 and 0.10) (LSPMCO) are investigated. LSPMCO crystallizes as a rhombohedral structure with $R$-$3c$ space group. As the Co content increases, the cell volume expands, the Mn-O-Mn bond angle reduces and the length of the Mn-O bond increases. The samples show irregular submicron particles under a Zeiss scanning electron microscopy. The particle size becomes larger with increasing doping. The chemical composition of the samples is confirmed by x-ray photoelectron spectroscopy (XPS). The ferromagnetic (FM) to paramagnetic (PM) phase transition occurs near the Curie temperature ($T_{\rm C}$), and all transitions are second-order phase transitions (SMOPT) characterized by minimal thermal and magnetic hystereses. Critical behavior analysis indicates that the critical parameters of LSPMCO closely align with those predicted by the mean-field model. The $T_{\rm C}$ declines with Co doping and reaches near room temperature (302 K) at $x = 0.075$. The maximum magnetic entropy change ($-\Delta S_{\rm M}^{\max}$) at $x = 0.05$ is 4.27 J/kg$\cdot$K, and the relative cooling power (RCP) peaks at 310.81 J/K. Therefore, the system holds significant potential for development as a magnetic refrigeration material, meriting further professional and objective evaluation.

Distance-dependent magnetization modulation induced by inter-superatomic interactions in Cr-doped Au₆Te₁₂Se₈ dimers Suggested by editors

Yurou Guan(官雨柔), Nanshu Liu(刘南舒), Cong Wang(王聪), Fei Pang(庞斐), Zhihai Cheng(程志海), and Wei Ji(季威)

Chin. Phys. B, 2024, 33 (12): 127502. DOI: 10.1088/1674-1056/ad8625

Abstract ( 34 )

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Individual superatoms are assembled into more complicated nanostructures to diversify their physical properties. Magnetism of assembled superatoms remains, however, ambiguous, particularly in terms of its distance dependence. Here, we report density functional theory calculations on the distance-dependent magnetism of transition metal embedded Au$_{6}$Te$_{8}$Se$_{12}$ (ATS) superatomic dimers. Among the four considered transition metals, which include V, Cr, Mn and Fe, the Cr-embedded Au$_{6}$Te$_{12}$Se$_{8}$ (Cr@ATS) is identified as the most suitable for exploring the inter-superatomic distance-dependent magnetism. We thus focused on Cr@ATS superatomic dimers and found an inter-superatomic magnetization-distance oscillation where three transitions occur for magnetic ordering and/or anisotropy at different inter-superatomic distances. As the inter-superatomic distance elongates, a ferromagnetism (FM)-to-antiferromagnetic (AFM) transition and a sequential AFM-to-FM transition occur, ascribed to competitions among Pauli repulsion and kinetic-energy-gains in formed inter-superatomic Cr-Au-Au-Cr covalent bonds and Te-Te quasi-covalent bonds. For the third transition, in-plane electronic hybridization contributes to the stabilization of the AFM configuration. This work unveils two mechanisms for tuning magnetism through non-covalent interactions and provides a strategy for manipulating magnetism in superatomic assemblies.

Valley modulation and topological phase transition in staggered kagome ferromagnets

Yuheng Xing(邢玉恒), Wenjuan Qiu(邱文娟), Xinxing Wu(吴新星), and Yue Tan(谭悦)

Chin. Phys. B, 2024, 33 (12): 127503. DOI: 10.1088/1674-1056/ad7af7

Abstract ( 38 )

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Owing to their charge-free property, magnons are highly promising for achieving dissipationless transport without Joule heating, and are thus potentially applicable to energy-efficient devices. Here, we investigate valley magnons and associated valley modulations in a kagome ferromagnetic lattice with staggered exchange interaction and Dzyaloshinskii-Moriya interaction. The staggered exchange interaction breaks the spatial inversion symmetry, leading to a valley magnon Hall effect. With nonzero Dzyaloshinskii-Moriya interaction in a staggered kagome lattice, the magnon Hall effect can be observed from only one valley. Moreover, reversing the Dzyaloshinskii-Moriya interaction ($D\to -D$) and exchanging $J_{1}$ and $J_{2}$ ($J_{1} \leftrightarrow J_{2}$) can also regulate the position of the unequal valleys. With increasing Dzyaloshinskii-Moriya interaction, a series of topological phase transitions appear when two bands come to touch and split at the valleys. The valley Hall effect and topological phase transitions observed in kagome magnon lattices can be realized in thin films of insulating ferromagnets such as Lu$_{2}$V$_{2}$O$_{7}$, and will extend the basis for magnonics applications in the future.

Cu-doped nanocomposite Pr₂Fe₁₄B/α-Fe ribbons with high (BH)_max Suggested by editors

Mehran Khan Alam, Shahzab Raza, Chengyong Gao(高成勇), Guangbing Han(韩广兵), and Shishou Kang(康仕寿)

Chin. Phys. B, 2024, 33 (12): 127504. DOI: 10.1088/1674-1056/ad8cba

Abstract ( 19 )

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The melt-spun ribbons of nominal composition Pr$_{9}$Fe$_{84.2-x}$B$_{6.2}$P$_{0.3}$Zr$_{0.3}$Cu$_{x}$ ($x=0$, 0.5, 1, 2) were prepared at wheel speeds of 21 m$\cdot$s$^{-1}$, 27 m$\cdot$s$^{-1}$, 30 m$\cdot$s$^{-1}$, and 33 m$\cdot$s$^{-1}$. The XRD patterns show that as the wheel speed increases, the crystallinity of the 2:14:1 hard phase decreases, while that of the $\alpha $-Fe soft phase increases. The $(BH)_{\rm max}$, remanence, and coercivity are improved from 63 kJ$\cdot$m$^{-3}$, 0.85 T, and 515 kA$\cdot$m$^{-1}$ for the Cu-free ribbons to 171 kJ$\cdot$m$^{-3}$, 1.08 T, and 684 kA$\cdot$m$^{-1}$ with $x=0.5$. The high squareness ratio of $J_{\rm r}/J_{\rm s} \sim 0.82$ at 0.5 at.% Cu (27 m$\cdot$s$^{-1}$) indicates strong exchange coupling due to small grain sizes of 15 nm and 30 nm for soft and hard magnetic phases, respectively. The SEM images revealed smooth morphology and uniform element distribution at 0.5 at.% Cu (27 m$\cdot$s$^{-1}$), contributing to the high magnetic properties. The low recoil permeability ($\mu_{\rm rec}$) value of $5.466\times {10}^{-4}$ T/kA$\cdot$m$^{-1}$ to $1.970\times {10}^{-4}$ T/kA$\cdot$m$^{-1}$ confirms the strong exchange coupling with $x=0.5$ (27 m$\cdot$s$^{-1}$). The initial magnetization curves show that the coercivity mechanism of the Cu-free alloy evolves from the nucleation of the reverse domain to the domain wall pinning as the wheel speed increases, resulting in a high coercivity value of 818 kA$\cdot$m$^{-1}$ (33 m$\cdot$s$^{-1}$). Conversely, for the Cu-added alloy, the coercivity mechanism changes from pinning to the nucleation of the reverse domain from low to high wheel speed.

Optical properties of La₂O₃ and HfO₂ for radiative cooling via multiscale simulations

Lihao Wang(王礼浩), Wanglin Yang(杨旺霖), Zhongyang Wang(王忠阳), Hongchao Li(李鸿超), Hao Gong(公昊), Jingyi Pan(潘静怡), Tongxiang Fan(范同祥), and Xiao Zhou(周啸)

Chin. Phys. B, 2024, 33 (12): 127801. DOI: 10.1088/1674-1056/ad84c0

Abstract ( 31 )

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Radiative cooling materials have gained prominence as a zero-energy solution for mitigating global warming. However, a comprehensive understanding of the atomic-scale optical properties and macroscopic optical performance of radiative cooling materials remains elusive, limiting insight into the underlying physics of their optical response and cooling efficacy. La$_{2}$O$_{3}$ and HfO$_{2}$, which represent rare earth and third/fourth subgroup inorganic oxides, respectively, show promise for radiative cooling applications. In this study, we used multiscale simulations to investigate the optical properties of La$_{2}$O$_{3}$ and HfO$_{2}$ across a broad spectrum. First-principles calculations revealed their dielectric functions and intrinsic refractive indices, and the results indicated that the slightly smaller bandgap of La$_{2}$O$_{3}$ compared to HfO$_{2}$ induces a higher refractive index in the solar band. Additionally, three-phonon scattering was found to provide more accurate infrared optical properties than two-phonon scattering, which enhanced the emissivity in the sky window. Monte Carlo simulations were also used to determine the macroscopic optical properties of La$_{2}$O$_{3}$ and HfO$_{2}$ coatings. Based on the simulated results, we identified that the particle size and particle volume fraction play a dominant role in the optical properties. Our findings underscore the potential of La$_{2}$O$_{3}$ and HfO$_{2}$ nanocomposites for environment-friendly cooling and offer a new approach for high-throughput screening of optical materials through multiscale simulations.

Enhanced near-field radiative heat transfer between borophene sheets on different substrates Suggested by editors

Xiaoyang Han(韩小洋) and Chunzhen Fan(范春珍)

Chin. Phys. B, 2024, 33 (12): 127802. DOI: 10.1088/1674-1056/ad84cd

Abstract ( 42 )

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Near-field radiative heat transfer (NFRHT) has the potential to exceed the blackbody limit by several orders of magnitude, offering significant opportunities for energy harvesting. In this study, we have examined the NFRHT between two borophene sheets through the calculation of heat transfer coefficient (HTC). Due to the tunneling of evanescent waves, borophene sheet allows for enhanced heat flux and adjustable NFRHT by varying its electron density and electron relaxation time. Additionally, the near field coupling is further examined when the borophene is deposited on dielectric or lossy substrates. The maximum HTC is closely related to the real part of the dielectric substrate. As a case study, the HTCs on the lossy substrate of MoO$_{3}$, ZnSe, and SiC are calculated for comparisons. Our results indicate that MoO$_{3}$ is the optimal substrate to get the enhanced energy transfer coefficient. It results in a remarkable value of 1737 times higher than the blackbody limit owing to the enhanced photon tunneling probability. Thus, our study reveals the effect of substrate on the HTC between borophene sheets and provides a theoretical guidance for the design of near-field thermal radiation devices.

Screening A-site ordered quadruple perovskites for alkaline hydrogen evolution reaction via unifying electronic configuration descriptor Suggested by editors

Ning Sun(孙宁), Wenbo Li(李文博), Yang Qin(秦杨), Zhichuan Zheng(郑智钏), Bowen Zhang(张博文), Xiangjiang Dong(董祥江), Peng Wei(魏鹏), Yixiao Zhang(张艺潇), Xian He(何贤), Xinyu Xie(谢新煜), Kai Huang(黄凯), Lailei Wu(吴来磊), Ming Lei(雷鸣), Huiyang Gou(缑慧阳), and Runze Yu(于润泽)

Chin. Phys. B, 2024, 33 (12): 128101. DOI: 10.1088/1674-1056/ad8074

Abstract ( 30 )

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Dynamic adsorption processes of reaction intermediates for alkaline hydrogen evolution (HER) catalysts are still confusing to understand. Here, we report a series of $A$-site ordered quadruple perovskite ruthenium-based electrocatalysts $A$Cu$_{3}$Ru$_{4}$O$_{12}$ ($A ={\rm Na}$, Ca, Nd, and La), with the target sample SrCu$_{3}$Ru$_{4}$O$_{12}$ exhibiting a very low overpotential (46 mV @10 mA$\cdot$ cm$^{-2}$) and excellent catalytic stability with little decays after 48-h durability test. Precise tuning $A$-site cations can change the average valence state of Cu and Ru, thus the plot of HER activity $versus$ the average Ru valence number shows a volcano-type relationship. Density functional theory indicates that the Ru 4d orbitals of SrCu$_{3}$Ru$_{4}$O$_{12}$ possesses the most suitable d-band center position among the five samples, which might be the key parameter to determine the catalytic performance. Our work provides further insight into the discovering advanced, efficient hydrogen evolution catalysts through designing precise descriptor.

Effects of TMIn flow rate during quantum barrier growth on multi-quantum well material properties and device performance of GaN-based laser diodes Suggested by editors

Zhenyu Chen(陈振宇), Degang Zhao(赵德刚), Feng Liang(梁锋), Zongshun Liu(刘宗顺), Jing Yang(杨静), and Ping Chen(陈平)

Chin. Phys. B, 2024, 33 (12): 128102. DOI: 10.1088/1674-1056/ad8624

Abstract ( 31 )

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Multidimensional influences of indium composition in barrier layers on GaN-based blue laser diodes (LDs) are discussed from both material quality and device physics perspectives. LDs with higher indium content in the barriers demonstrate a notably lower threshold current and shorter lasing wavelength compared to those with lower indium content. Our experiments reveal that higher indium content in the barrier layers can partially reduce indium composition in the quantum wells, a novel discovery. Employing higher indium content barrier layers leads to improved luminescence properties of the MQW region. Detailed analysis reveals that this improvement can be attributed to better homogeneity in the indium composition of the well layers along the epitaxy direction. InGaN barrier layers suppress the lattice mismatch between barrier and well layers, thus mitigating the indium content pulling effect in the well layers. In supplement to experimental analysis, theoretical computations are performed, showing that InGaN barrier structures can effectively enhance carrier recombination efficiency and optical confinement of LD structure, thus improving the output efficiency of GaN-based blue LDs. Combining these theoretical insights with our experimental data, we propose that higher indium content barriers effectively enhance carrier recombination efficiency and indium content homogeneity in quantum well layers, thereby improving the output performance of GaN-based blue LDs.

Quantum-mechanical understanding on structure dependence of image potentials of single-walled boron nitride nanotubes Suggested by editors

Yu Zhang(张煜), Zhiman Zhang(张芷蔓), Weiliang Wang(王伟良), Shaolin Zhang(张绍林), and Haiming Huang(黄海鸣)

Chin. Phys. B, 2024, 33 (12): 128501. DOI: 10.1088/1674-1056/ad8071

Abstract ( 35 )

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The recent discovery of field emission devices based on one-dimensional nanostructures has attracted much interest in emerging applications on next-generation flat panel displays, molecule-based sensors, and so forth. To achieve a comprehensive understanding of surface potentials at the nano-emitters during the tunneling process, in this study we systematically investigated the image potentials of single-walled boron nitride nanotubes with different edges, diameters and lengths in the frame of a composite first-principles calculation. The image potentials of zigzag single-walled boron nitride nanotubes are found to be dependent on the non-equivalent sides. Only the image potentials of isolated armchair single-walled boron nitride nanotube can be well fitted with the image potential of an ideal metal sphere of a size comparable to the tube diameter. On the contrary, the image potentials of zigzag and grounded armchair single-walled boron nitride nanotubes exhibit a strong length-dependence characteristic and are significantly different from that of an ideal metal sphere, which originates from the significant axial symmetry breaking of induced charge at the tip for the long tube. The correlation between the testing electron and electronic structure of single-walled boron nitride nanotube has also been discussed.

A macro model of spin-transfer torque magnetic tunnel junction Suggested by editors

Ming-Bo Chen(陈明博), Kun-Kun Li(李琨琨), Xiao-Lei Yang(杨晓蕾), Xue Peng(彭雪), Wang-Da Li(李旺达), En-Long Liu(刘恩隆), Hui-Zhen Wu(吴惠桢), and Shi-Kun He(何世坤)

Chin. Phys. B, 2024, 33 (12): 128502. DOI: 10.1088/1674-1056/ad8072

Abstract ( 25 )

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The precise compact modeling of magnetic devices is pivotal for the integrated design of spin-transfer torque magnetic tunnel junction (STT-MTJ) in conjunction with CMOS circuitry. This work presents a macro model for an STT-MTJ which is compatible with SPICE simulation platforms. The model accurately replicates the electrical performance of the MTJ, encompassing the resistance-voltage characteristics and the pulse-width-dependent state switching behavior, and is validated with various experimental data. Additionally, the impact of process variations, particularly those affecting the MTJ diameter and barrier thickness is investigated and summarized in a corner model. Monte Carlo simulations demonstrate that our adaptable and streamlined model can be efficiently incorporated into the design of integrated circuits.

Back-side stress to ease p-MOSFET degradation on e-MRAM chips

Zhi-Meng Yu(于志猛), Xiao-Lei Yang(杨晓蕾), Xiao-Nan Zhao(赵晓楠), Yan-Jie Li(李艳杰), Shi-Kun He(何世坤), and Ye-Wu Wang(王业伍)

Chin. Phys. B, 2024, 33 (12): 128503. DOI: 10.1088/1674-1056/ad7c2d

Abstract ( 37 )

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The magnetoresistive random access memory process makes a great contribution to threshold voltage deterioration of metal-oxide-silicon field-effect transistors, especially on p-type devices. Herein, a method was proposed to reduce the threshold voltage degradation by utilizing back-side stress. Through the deposition of tensile material on the back side, positive charges generated by silicon-hydrogen bond breakage were inhibited, resulting in a potential reduction in threshold voltage shift by up to 20%. In addition, it was found that the method could only relieve silicon-hydrogen bond breakage physically, thus failing to provide a complete cure. However, it holds significant potential for applications where additional thermal budget is undesired. Furthermore, it was also concluded that the method used in this work is irreversible, with its effect sustained to the chip package phase, and it ensures competitive reliability of the resulting magnetic tunnel junction devices.

Influences of short-term and long-term plasticity of memristive synapse on firing activity of neuronal network Suggested by editors

Zhi-Jun Li(李志军) and Jing Zhang(张晶)

Chin. Phys. B, 2024, 33 (12): 128701. DOI: 10.1088/1674-1056/ad84c5

Abstract ( 34 )

PDF (5348KB) ( 10 )

Synaptic plasticity can greatly affect the firing behavior of neural networks, and it specifically refers to changes in the strength, morphology, and function of synaptic connections. In this paper, a novel memristor model, which can be configured as a volatile and nonvolatile memristor by adjusting its internal parameter, is proposed to mimic the short-term and long-term synaptic plasticity. Then, a bi-neuron network model, with the proposed memristor serving as a coupling synapse and the external electromagnetic radiation being emulated by the flux-controlled memristors, is established to elucidate the effects of short-term and long-term synaptic plasticity on firing activity of the neuron network. The resultant seven-dimensional (7D) neuron network has no equilibrium point and its hidden dynamical behavior is revealed by phase diagram, time series, bifurcation diagram, Lyapunov exponent spectrum, and two-dimensional (2D) dynamic map. Our results show the short-term and long-term plasticity can induce different bifurcation scenarios when the coupling strength increases. In addition, memristor synaptic plasticity has a great influence on the distribution of firing patterns in the parameter space. More interestingly, when exploring the synchronous firing behavior of two neurons, the two neurons can gradually achieve phase synchronization as the coupling strength increases along the opposite directions under two different memory attributes. Finally, a microcontroller-based hardware system is implemented to verify the numerical simulation results.

A Weibo local network growth model constructed from the perspective of following-followed Suggested by editors

Fu-Zhong Nian(年福忠) and Ran-Qing Yao(姚然庆)

Chin. Phys. B, 2024, 33 (12): 128702. DOI: 10.1088/1674-1056/ad84c4

Abstract ( 26 )

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In order to explore the evolution process of the Weibo local network, this study first defines four factors influencing the evolution of the Weibo network. On this basis, the BA scale-free network model was enhanced by incorporating these four factors and accounting for directionality, resulting in a Weibo local network evolution model based on user attributes and behavioral similarity. The model's validity was validated by comparing simulation results with real data. The findings indicate that the Weibo local network exhibits both small-world characteristics and distinctive features. The results show that the Weibo local network exhibits both small-world characteristics and distinctive properties. The in-degree distribution follows a mixed pattern of exponential and power-law distributions, the degree-degree shows isomatching, and both the in-degree centrality and eigenvector centrality values are relatively low. This research contributes to our understanding of user behaviour in the Weibo network, and provides a structural basis for exploring the impact of Weibo network structure on information dissemination.

Effect of different injection strategies considering intravenous injection on combination therapy of magnetic hyperthermia and thermosensitive liposomes Suggested by editors

Jiajia Zhu(朱佳佳), Yundong Tang(汤云东), Rodolfo C. C. Flesch(弗莱施 C. C. 鲁道夫), and Tao Jin(金涛)

Chin. Phys. B, 2024, 33 (12): 128703. DOI: 10.1088/1674-1056/ad8a48

Abstract ( 24 )

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The combination therapy of magnetic hyperthermia and thermosensitive liposomes (TSL) is an emerging and effective cancer treatment method. The heat generation of magnetic nanoparticles (MNPs) due to an external alternating magnetic field can not only directly damage tumor cells, but also serves as a triggering factor for the release of doxorubicin from TSL. The aim of this study is to investigate the effects in the degree of tumor cell damage of two proposed injection strategies that consider intravenous administration. Since both MNPs and TSL enter the tumor region intravenously, this study establishes a biological geometric model based on an experiment-based vascular distribution. Furthermore, this study derives the flow velocity of interstitial fluid after coupling the pressure distribution inside blood vessels and the pressure distribution of interstitial fluid, which then provides the convective velocity for the calculation of subsequent nanoparticle concentration. Different injection strategies for the proposed approach are evaluated by drug delivery result, temperature distribution, and tumor cell damage. Simulation results demonstrate that the proposed delayed injection strategy after optimization can not only result in a wider distribution for MNPs and TSL due to the sufficient diffusion time, but also improves the distribution of the temperature and drug concentration fields for the overall efficacy of combination therapy.

Simulation of crowd evacuation under attack considering emotion spreading

Yang Wang(王杨), Ning Ding(丁宁), Dapeng Dong(董大鹏), and Yu Zhu(朱萸)

Chin. Phys. B, 2024, 33 (12): 128901. DOI: 10.1088/1674-1056/ad84c7

Abstract ( 44 )

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In recent years, attacks against crowded places such as campuses and theaters have had a frequent and negative impact on the security and stability of society. In such an event, the crowd will be subjected to high psychological stress and their emotions will rapidly spread to others. This paper establishes the attack-escape evacuation simulation model (AEES-SFM), based on the social force model, to consider emotion spreading under attack. In this model, (1) the attack-escape driving force is considered for the interaction between an attacker and evacuees and (2) emotion spreading among the evacuees is considered to modify the value of the psychological force. To validate the simulation, several experiments were carried out at a university in China. Comparing the simulation and experimental results, it is found that the simulation results are similar to the experimental results when considering emotion spreading. Therefore, the AEES-SFM is proved to be effective. By comparing the results of the evacuation simulation without emotion spreading, the emotion spreading model reduces the evacuation time and the number of casualties by about 30%, which is closer to the real experimental results. The results are still applicable in the case of a 40-person evacuation. This paper provides theoretical support and practical guidance for campus response to violent attacks.

Hyperbolic map unravels eight regions in temperature volatility regionalization of Mainland China Suggested by editors

Yuxuan Song(宋雨轩), Changgui Gu(顾长贵), Muhua Zheng(郑木华), Aixia Feng(冯爱霞), Yufei Xi(席雨菲), Haiying Wang(王海英), and Huijie Yang(杨会杰)

Chin. Phys. B, 2024, 33 (12): 128902. DOI: 10.1088/1674-1056/ad84c2

Abstract ( 19 )

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Abrupt temperature volatility has detrimental effects on daily activities, macroeconomic growth, and human health. Predicting abrupt temperature volatility and thus diminishing its negative impacts can be achieved by exploring homogeneous regions of temperature volatility and analyzing the driving factors. To investigate the regionalization of temperature volatility in Mainland China, a network constructed by the cosine similarity of temperature volatility series from Mainland China was embedded in hyperbolic space. Subsequently, we partitioned the network on the hyperbolic map using the critical gap method and then found eight regions in all. Ultimately, a network of communities was constructed while the interaction among communities was quantified. This yields a perspective of temperature volatility regionalization that can accurately reflect factors including altitude, climate type, and the geographic location of mountains. Further analysis demonstrates that the regionalization in the hyperbolic map is distinct from provinces and has a realistic basis: communities in southwest China show strong correlations due to the temperature sensitivity to altitude, and communities in northern China show a convergence in the area of Dingxi, Gansu, mainly owing to the strong temperature sensitivity to climate types. As a consequence, node distributions and community divisions in the hyperbolic map can offer new insights into the regionalization of temperature volatility in Mainland China. The results demonstrate the potential of hyperbolic embedding of complex networks in forecasting future node associations in real-world data.

Impact of environmental factors on the coevolution of information-emotions-epidemic dynamics in activity-driven multiplex networks

Liang'an Huo(霍良安), Bingjie Liu(刘炳杰), and Xiaomin Zhao(赵晓敏)

Chin. Phys. B, 2024, 33 (12): 128903. DOI: 10.1088/1674-1056/ad7df5

Abstract ( 39 )

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During public health emergencies, the diffusion of negative information can exacerbate the transmission of adverse emotions, such as fear and anxiety. These emotions can adversely affect immune function and, consequently, influence the spread of the epidemic. In this study, we established a coupled model incorporating environmental factors to explore the coevolution dynamic process of information-emotions-epidemic dynamics in activity-driven multiplex networks. In this model, environmental factors refer to the external conditions or pressures that affect the spread of information, emotions, and epidemics. These factors include media coverage, public opinion, and the prevalence of diseases in the neighborhood. These layers are dynamically cross-coupled, where the environmental factors in the information layer are influenced by the emotional layer; the higher the levels of anxious states among neighboring individuals, the greater the likelihood of information diffusion. Although environmental factors in the emotional layer are influenced by both the information and epidemic layers, they come from the factors of global information and the proportion of local infections among surrounding neighbors. Subsequently, we utilized the microscopic Markov chain approach to describe the dynamic processes, thereby obtaining the epidemic threshold. Finally, conclusions are drawn through numerical modeling and analysis. The conclusions suggest that when negative information increases, the probability of the transmission of anxious states across the population increases. The transmission of anxious states increases the final size of the disease and decreases its outbreak threshold. Reducing the impact of environmental factors at both the informational and emotional levels is beneficial for controlling the scale of the spread of the epidemic. Our findings can provide a reference for improving public health awareness and behavioral decision-making, mitigating the adverse impacts of anxious states, and ultimately controlling the spread of epidemics.

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