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Chirality transfer torque and transverse Chirality current in the Dirac/magnetic Weyl semimetal junction 狄拉克/磁性韦尔半金属结中的手性传递扭矩和横向手性电流
IF 2.9 3区 物理与天体物理 Q2 PHYSICS, MULTIDISCIPLINARY Pub Date : 2024-09-12 DOI: 10.1088/1402-4896/ad7547
Morteza Salehi
We theoretically show that an interface formed by a three-dimensional Dirac/magnetic Weyl semimetal deflects the propagation direction of hitting Weyl fermions according to their Chirality in opposite directions. This effect leads to a Chirality current that flows parallel to the interface. There is an imbalance between the Chirality of Weyl fermions in this current whereas it does not carry any charge. Also, this phenomenon creates an indirect gap in the charge conductance that pass through the circuit. Unlike real spin, Chirality remains a good quantum number in systems characterized by very strong spin-momentum coupling. We derive a continuity equation for the Chirality density wave to elucidate how magnetization alters its dynamics and relates to the transverse Chirality current. Furthermore, we demonstrate a torque, that we called it Chirality transfer torque, imposes on the junction that its value relates to the transverse Chirality current.
我们从理论上证明,由三维狄拉克/磁性韦尔半金属形成的界面会使撞击韦尔费米子的传播方向根据其奇异性向相反方向偏转。这种效应导致了平行于界面的手性电流。在这一电流中,Weyl 费米子的手性之间存在不平衡,而它并不携带任何电荷。此外,这种现象还会在通过电路的电荷传导中产生间接间隙。与真实自旋不同,手性在自旋-动量耦合非常强的系统中仍然是一个很好的量子数。我们推导出了手性密度波的连续性方程,以阐明磁化如何改变其动态以及与横向手性电流的关系。此外,我们还证明了一种我们称之为手性传递力矩(Chirality transfer torque)的力矩,它施加在结点上,其值与横向手性电流有关。
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引用次数: 0
Transition to chaos in magnetized rotating Rayleigh-Bénard convection 磁化旋转瑞利-贝纳德对流向混沌的过渡
IF 2.9 3区 物理与天体物理 Q2 PHYSICS, MULTIDISCIPLINARY Pub Date : 2024-09-12 DOI: 10.1088/1402-4896/ad741e
Dalton N Oliveira, Roman Chertovskih, Erico L Rempel and Francis F Franco
Transition to chaos and magnetic field generation are investigated in numerical simulations of three-dimensional rotating Rayleigh-Bénard convection. The behavior of the system is explored as a function of the rotation speed, measured by the Taylor number, the thermal buoyancy strength, measured by the Rayleigh number, and the magnetic Prandtl number. In the absence of magnetic field, a detailed exploration of the space of parameters reveals a sequence of Hopf bifurcations leading to quasiperiodicity and chaos. It is shown that rotation can dampen convection for low values of the Rayleigh number, but if buoyancy is strong enough to keep the convection, then rotation facilitates transition to chaos. In the presence of a weak seed magnetic field, convective motions may trigger a nonlinear dynamo that converts kinetic energy into magnetic energy, leading to an exponential increase of the magnetic energy. A nonhysteretic blowout bifurcation is shown to be responsible for the onset of the dynamo regime for a critical magnetic Prandtl number, whose value depends on the rotation rate.
在三维旋转瑞利-贝纳德对流的数值模拟中研究了向混沌的过渡和磁场的产生。研究探讨了系统行为与旋转速度(以泰勒数衡量)、热浮力强度(以瑞利数衡量)和磁性普朗特数的函数关系。在没有磁场的情况下,对参数空间的详细探索揭示了一系列导致准周期性和混沌的霍普夫分岔。研究表明,在雷利数数值较低时,旋转可以抑制对流,但如果浮力足够强大以保持对流,则旋转会促进向混沌过渡。在存在弱种子磁场的情况下,对流运动可能会引发非线性发电机,将动能转化为磁能,从而导致磁能呈指数增长。研究表明,在临界磁普朗特尔数(其值取决于旋转速率)条件下,非滞后性井喷分岔是引发动力机制的原因。
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引用次数: 0
Theory of size quantization in monolayers of transition metal dichalcogenides 过渡金属二卤化物单层尺寸量化理论
IF 2.9 3区 物理与天体物理 Q2 PHYSICS, MULTIDISCIPLINARY Pub Date : 2024-09-12 DOI: 10.1088/1402-4896/ad7546
V R Rasulov, R Ya Rasulov, M Kh Nasirov, I A Muminov and M M Mamatova
A theory of size quantization has been developed for both one-dimensional and zero-dimensional nanostructures, grown from monolayers of transition metal dichalcogenides. Expressions for the energy spectra of charge carriers have been obtained for both even and odd (relative to coordinate inversion) states in the quantum-confined line and point of monolayers of transition metal dichalcogenides, depending on their geometric dimensions. A numerical analysis of the quantum-confined energy states of electrons in nanostructures of monolayers of transition metal dichalcogenides has been conducted.
针对由过渡金属二卤化物单层生长而成的一维和零维纳米结构,提出了尺寸量子化理论。根据过渡金属二卤化物单层的几何尺寸,我们获得了其量子约束线和点的偶数态和奇数态(相对于坐标反转)电荷载流子能谱的表达式。对过渡金属二钙化物单层纳米结构中电子的量子约束能态进行了数值分析。
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引用次数: 0
Time domain optimization of pair production during vacuum breakdown triggered by frequency chirped external fields 在频率啁啾外场触发的真空击穿过程中对生产的时域优化
IF 2.9 3区 物理与天体物理 Q2 PHYSICS, MULTIDISCIPLINARY Pub Date : 2024-09-12 DOI: 10.1088/1402-4896/ad7331
Chi Gong, Xinyu Lu, Dakai Shang, Zhi Ren and Songtao Li
The electron–positron pair creation process during the Dirac vacuum breakdown triggered by strong external fields is analyzed. A frequency chirped, subcritical force field can significantly enhance the pair production yield under the identical total energy. This enhancement effect is caused by different chirp frequencies. We pay special attention to optimal field conditions as chirping parameter and phase of the time dependent field are varied. And the total number of created electrons with frequency weighted average under different chirp parameters are different from the theoretically calculated values. And no matter what the main mechanism is, the laser has the highest energy utilization rate when the electric field is symmetrical.
分析了强外力场引发的狄拉克真空击穿过程中的电子-正电子对产生过程。在总能量相同的情况下,频率啁啾的亚临界力场可以显著提高电子对产生率。这种增强效应是由不同的啁啾频率引起的。随着啁啾参数和随时间变化的力场相位的变化,我们特别关注了最佳力场条件。在不同的啁啾参数下,产生的电子总数的频率加权平均值与理论计算值不同。无论主要机制是什么,当电场对称时,激光的能量利用率最高。
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引用次数: 0
Periodicity of bipartite walk on biregular graphs with conditional spectra 具有条件谱的双翼图上双翼行走的周期性
IF 2.9 3区 物理与天体物理 Q2 PHYSICS, MULTIDISCIPLINARY Pub Date : 2024-09-12 DOI: 10.1088/1402-4896/ad71ff
Qiuting Chen
In this paper we study a class of discrete quantum walks, known as bipartite walks. These include the well-known Grover’s walks. A discrete quantum walk is given by the powers of a unitary matrix U indexed by arcs or edges of the underlying graph. The walk is periodic if Uk = I for some positive integer k. Kubota has given a characterization of periodicity of Grover’s walk when the walk is defined on a regular bipartite graph with at most five eigenvalues. We extend Kubota’s results—if a biregular graph G has eigenvalues whose squares are algebraic integers with degree at most two, we characterize periodicity of the bipartite walk over G in terms of its spectrum. We apply periodicity results of bipartite walks to get a characterization of periodicity of Grover’s walk on regular graphs.
在本文中,我们研究了一类离散量子漫步,即所谓的二方漫步。其中包括著名的格罗弗漫步。离散量子漫步由以底层图的弧或边为索引的单元矩阵 U 的幂给出。当格罗弗漫步定义在最多有五个特征值的规则二方图上时,久保田给出了格罗弗漫步周期性的特征。我们扩展了久保田的结果--如果一个双线形图 G 的特征值的平方是代数整数,且最多有两个阶,那么我们就用它的谱来描述 G 上双线形行走的周期性。我们应用双方位行走的周期性结果,得到格罗弗行走在规则图上的周期性特征。
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引用次数: 0
Entanglement enhancement of two giant atoms with multiple connection points in bidirectional-chiral quantum waveguide-QED system 双向手性量子波导-QED 系统中具有多个连接点的两个巨原子的纠缠增强
IF 2.9 3区 物理与天体物理 Q2 PHYSICS, MULTIDISCIPLINARY Pub Date : 2024-09-12 DOI: 10.1088/1402-4896/ad75c0
Jie Liu, Yue Cai, Kang-Jie Ma, Lei Tan and Wu-Ming Liu
We study the entanglement generation of two giant atoms within a one-dimensional bidirectional-chiral waveguide quantum electrodynamics (QED) system, where the initial state of the two giant atoms are ∣ea, gb〉. Here, each giant atom is coupled to the waveguide through three connection points, with the configurations divided into five types based on the arrangement of coupling points between the giant atoms and the waveguide: separate, fully braided, partially braided, fully nested, and partially nested. We explore the entanglement generation process within each configuration in both nonchiral and chiral coupling cases. It is demonstrated that entanglement can be controlled as needed by either adjusting the phase shift or selecting different configurations. For nonchiral coupling, the entanglement of each configuration exhibits steady state properties attributable to the presence of dark state. In addition, we find that steady-state entanglement can be obtained at more phase shifts in certain configurations by increasing the number of coupling points between the giant atoms and the bidirectional waveguide. In the case of chiral coupling, the entanglement is maximally enhanced compared to the one of nonchiral case. Especially in fully braided configuration, the concurrence reaches its peak value 1, which is robust to chirality. We further show the influence of atomic initial states on the evolution of interatomic entanglement. Our scheme can be used for entanglement generation in chiral quantum networks of giant-atom waveguide-QED systems, with potential applications in quantum networks and quantum communications.
我们研究了两个巨原子在一维双向手性波导量子电动力学(QED)系统中纠缠的产生,其中两个巨原子的初始状态分别为∣ea, gb〉。在这里,每个巨原子通过三个连接点与波导耦合,根据巨原子与波导之间耦合点的排列,配置分为五种类型:分离型、完全编织型、部分编织型、完全嵌套型和部分嵌套型。我们探讨了非手性和手性耦合情况下每种构型中纠缠的产生过程。结果表明,纠缠可以根据需要通过调整相移或选择不同的配置来控制。对于非手性耦合,每个构型的纠缠都表现出稳态特性,这归因于暗态的存在。此外,我们还发现,通过增加巨原子与双向波导之间的耦合点数量,可以在某些构型中以更多的相移获得稳态纠缠。与非手性情况相比,手性耦合情况下的纠缠得到了最大程度的增强。特别是在全编织结构中,并合达到了峰值 1,这对手性是稳健的。我们进一步展示了原子初始状态对原子间纠缠演化的影响。我们的方案可用于巨原子波导-QED 系统手性量子网络中的纠缠生成,在量子网络和量子通信中具有潜在的应用前景。
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引用次数: 0
Analytical study of the thermoelectric properties in silicene 硅的热电特性分析研究
IF 2.9 3区 物理与天体物理 Q2 PHYSICS, MULTIDISCIPLINARY Pub Date : 2024-09-12 DOI: 10.1088/1402-4896/ad7414
R Amarnath, K S Bhargavi and S S Kubakaddi
Theoretically, we investigate the thermoelectric (TE) properties namely, electrical conductivity (σ), diffusion thermopower (Sd), power factor (PF), electronic thermal conductivity (κe) and thermoelectric figure of merit (ZT) for silicene on Al2O3 substrate. TE coefficients are obtained by solving the Boltzmann transport equation taking account of the electron scattering by all the relevant scattering mechanisms in silicene, namely charged impurity (CI), short-range disorder (SD), intra- and inter-valley acoustic (APs) and optical (OPs) phonons, and surface optical phonons (SOPs). The TE properties are numerically studied as a function of temperature T (2–400K) and electron concentration ns(0.1–10 × 1012 cm−2). The calculated σ and Sdare found to be governed by CIs at low temperatures (T< ∼ 10 K), similar to that in graphene. At higher T, they are found to be mainly dominated by the intra- and inter-valley APs. The resultant σ (Sd) is found to decrease (increase) with increasing T, whereas PF remains nearly constant for T> ∼ 100 K. On the other hand, ns dependence shows that σ (Sd) increases (decreases) with increasing ns; with PF relatively constant at lower ns and then decreases with increasing ns. At room temperature, the calculated σ (Sd) in silicene is closer to that in graphene and about an order of magnitude greater (less) than that in monolayer (ML) MoS2. The κe is found to be weakly depending on T and Wiedemann–Franz law is shown to be violated. We have predicted a maximum PF ∼3.5 mW m−1 K−2, at 300 K for ns = 0.1 × 1012 cm−2 from which the estimated ZT = 0.11, taking a theoretically predicted lattice thermal conductivity κl = 9.4 Wm−1 K−1, is a maximum. This ZT is much greater than that of graphene and ML MoS2. The ZT is found to decrease with the increasing ns. The ZT values for other values of ns in silicene, at 300 K, also show much superiority over graphene, thus making silicene a preferred thermoelectric material because of its relatively large σ and very small κl.
我们从理论上研究了硅烯在 Al2O3 衬底上的热电(TE)特性,即导电率 (σ)、扩散热功率 (Sd)、功率因数 (PF)、电子热导率 (κe)和热电优点系数 (ZT)。TE 系数是通过求解波尔兹曼输运方程得到的,其中考虑了硅烯中所有相关散射机制的电子散射,即带电杂质(CI)、短程无序(SD)、谷内和谷间声子(APs)和光学声子(OPs)以及表面光学声子(SOPs)。数值研究了 TE 特性与温度 T(2-400K)和电子浓度 ns(0.1-10 × 1012 cm-2)的函数关系。计算得出的 σ 和 Sd 在低温(T< ∼ 10 K)下受 CIs 控制,与石墨烯的情况类似。在较高温度下,它们主要由谷内和谷间 AP 主导。另一方面,ns 依赖性表明 σ (Sd) 随着 ns 的增加而增加(减少);PF 在较低 ns 时相对恒定,然后随着 ns 的增加而减少。在室温下,硅烯的计算σ(Sd)更接近石墨烯的计算σ(Sd),比单层(ML)MoS2 的计算σ(Sd)高(低)一个数量级。我们发现κe 微弱地依赖于 T,并证明违反了 Wiedemann-Franz 定律。我们预测在 ns = 0.1 × 1012 cm-2 时,300 K 的最大 PF ∼3.5 mW m-1 K-2,根据理论预测的晶格热导率 κl = 9.4 Wm-1 K-1,估计 ZT = 0.11。该 ZT 远远大于石墨烯和 ML MoS2 的 ZT。随着 ns 的增大,ZT 值会减小。在 300 K 时,硅烯中其他 ns 值的 ZT 值也比石墨烯高出很多,因此硅烯因其相对较大的 σ 和极小的 κl 而成为首选热电材料。
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引用次数: 0
A novel design of energy absorption branch for HVDC circuit breakers 高压直流断路器能量吸收支路的新型设计
IF 2.9 3区 物理与天体物理 Q2 PHYSICS, MULTIDISCIPLINARY Pub Date : 2024-09-12 DOI: 10.1088/1402-4896/ad75c3
Guoqiang Gao, Bingyan You, Yaguang Ma, Aozheng Wang, Wei Peng, Pengyu Qian, Yu Xiang, Zefeng Yang, Wenfu Wei and Guangning Wu
Metal oxide varistors (MOV) used for energy absorption branch in DC circuit breakers are complex enough to meet the requirements for small volume, light weight, and reliability in future high-voltage direct current (HVDC) grids. Therefore, a new energy absorption branch circuit that combines MOV and a liquid metal alloy energy absorber (LMEA) is proposed. Based on the constructed equivalent mathematical model of LMEA, the working principle and energy absorption process of MOV and LMEA in DC breaking process are analysed in PSCAD/EMTDC simulation software. Results demonstrate that LMEA, in contrast to MOV alone, absorbs 2.12 MJ of energy, constituting 35.6% of the total energy. Moreover, LMEA enhances energy dissipation density while reducing volume. Experimental analysis reveals MOV’s energy absorption mechanism via achieving residual voltage with ZnO varistor’s non-linear properties, swiftly transitioning from high to low resistance states to absorb energy. Conversely, LMEA relies on pulse current amplitude to initiate internal arcing, sharply increasing internal resistance for effective energy absorption. Experimental findings validate LMEA’s contribution of one-third of total energy absorption when pulse current amplitude reaches critical arcing threshold, consistent with simulation results. The results provide theoretical support for the engineering application of the new liquid metal alloy energy absorption in DC circuit breakers.
用于直流断路器能量吸收支路的金属氧化物压敏电阻(MOV)非常复杂,难以满足未来高压直流(HVDC)电网对体积小、重量轻和可靠性的要求。因此,我们提出了一种结合 MOV 和液态金属合金能量吸收器(LMEA)的新型能量吸收支路。基于所构建的 LMEA 等效数学模型,在 PSCAD/EMTDC 仿真软件中分析了 MOV 和 LMEA 在直流分断过程中的工作原理和能量吸收过程。结果表明,与单独使用 MOV 相比,LMEA 可吸收 2.12 兆焦耳的能量,占总能量的 35.6%。此外,LMEA 在减小体积的同时提高了能量耗散密度。实验分析表明,MOV 的能量吸收机制是利用 ZnO 变阻器的非线性特性实现残压,迅速从高阻态过渡到低阻态以吸收能量。相反,LMEA 依靠脉冲电流振幅启动内部电弧,急剧增加内部电阻,从而有效吸收能量。实验结果验证了当脉冲电流幅值达到临界电弧阈值时,LMEA 能够吸收总能量的三分之一,这与模拟结果一致。这些结果为直流断路器中新型液态金属合金能量吸收的工程应用提供了理论支持。
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引用次数: 0
Dynamics of memristive circuit driven by Josephson junction 约瑟夫森结驱动的记忆电路动力学
IF 2.9 3区 物理与天体物理 Q2 PHYSICS, MULTIDISCIPLINARY Pub Date : 2024-09-12 DOI: 10.1088/1402-4896/ad7650
Cuimei Jiang, Xuejing Gu, Fangfang Zhang, Jian Liu and Pengfei Liu
The nonlinear circuit with charge-controlled memristor (CCM) can capture the external electric field effect. The nonlinear circuit with Josephson junction (JJ) can estimate the external magnetic field effect. Therefore, we propose an enhanced functional circuit by connecting a CCM and a JJ into a simple RLC nonlinear circuit. This enchanced circuit can estimate the external electromagnetic fields concurrently. The dynamical equations of the new memristive circuit and its Hamilton energy function are obtained by using the Kirchhoff’s law and the Helmholtz’s theorem. Furthermore, the complex dynamics of memristive circuit are investigated by applying bifurcation diagrams, Lyapunov exponents and time sampled series. The simulation experiment results indicate that the electromagnetic field has a great influence on complex dynamics of memristive circuit. In fact, this new nonlinear circuit is also a functional neural circuit, and it can be used to study the collective dynamic of functional neural network under the condition of an external electromagnetic fields.
带有电荷控制忆阻器(CCM)的非线性电路可以捕捉外部电场效应。带有约瑟夫森结(JJ)的非线性电路可以估计外部磁场效应。因此,我们提出了一种将 CCM 和 JJ 连接到简单 RLC 非线性电路中的增强型功能电路。这种增强电路可以同时估算外部电磁场。利用基尔霍夫定律和亥姆霍兹定理,我们得到了新型记忆电路的动力学方程及其汉密尔顿能量函数。此外,还利用分岔图、Lyapunov 指数和时间采样序列研究了忆阻电路的复杂动力学。模拟实验结果表明,电磁场对记忆电路的复杂动力学有很大影响。事实上,这种新的非线性电路也是一种功能神经回路,可用于研究外部电磁场条件下功能神经网络的集体动力学。
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引用次数: 0
A room-temperature ultrafast carrier dynamical study and thickness-dependent investigation of WTe2 thin films on a flexible PET substrate 柔性 PET 基底上的 WTe2 薄膜的室温超快载流子动力学研究和厚度依赖性调查
IF 2.9 3区 物理与天体物理 Q2 PHYSICS, MULTIDISCIPLINARY Pub Date : 2024-09-12 DOI: 10.1088/1402-4896/ad75d3
Sahil Verma, Kapil Kumar, Reena Yadav, Animesh Pandey, Mandeep Kaur, Mahesh Kumar and Sudhir Husale
In the current era of increasing demand for optoelectronic-based devices with ultra-rapid response, it is important to understand the processes associated with the relaxation dynamics of hot carriers and transient electrical properties of WTe2 material under photoexcitation of charge carriers. In this work, using femtosecond laser pump–probe spectroscopy at room temperature we performed the transient absorption measurement on sputtered deposited WTe2 thin films having four different thicknesses to study dynamics associated with the relaxation of their hot carriers. The relaxation dynamics of photoexcited charge carriers undergo three exponential decay components associated with electron–phonon thermalization in the conduction band and phonon-assisted electron–hole recombination between the electron and hole pocket. The thickness-dependent investigation of WTe2 thin films reveals that the electron–hole recombination process is more prominent in thicker films than in thinner films, supporting previously published theoretical and experimental conclusions. The Ultrafast study of WTe2 thin films suggests that it is a suitable material for future ultrafast optoelectronic-based device applications.
当今时代对基于光电的超快速响应设备的需求日益增长,因此了解热载流子的弛豫动力学过程以及 WTe2 材料在电荷载流子光激发下的瞬态电特性非常重要。在这项研究中,我们利用飞秒激光泵浦探针光谱技术,在室温下对四种不同厚度的溅射沉积 WTe2 薄膜进行了瞬态吸收测量,以研究与热载流子弛豫相关的动力学过程。光激发电荷载流子的弛豫动力学经历了三个指数衰减分量,分别与导带中的电子-声子热化以及电子和空穴之间的声子辅助电子-空穴重组有关。对 WTe2 薄膜厚度依赖性的研究表明,较厚薄膜中的电子-空穴重组过程比较薄薄膜中更为突出,这支持了之前发表的理论和实验结论。对 WTe2 薄膜的超快研究表明,它是未来基于超快光电器件应用的一种合适材料。
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引用次数: 0
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