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Quantized perfect transmission in graphene nanoribbons with random hollow adsorbates

Physical Review B 2024年第6期110卷 064201-064201页

作者： Jia-Le Yu Zhe Hou Irfan Hussain Bhat Pei-Jia Hu Jia-Wen Sun Xiao-Feng Chen Ai-Min Guo Qing-Feng Sun Hunan Key Laboratory for Super-microstructure and Ultrafast Process School of Physics School of Physics and Technology School of Physical Science and Technology International Center for Quantum Materials School of Physics Hefei National Laboratory Hefei 230088 China

Impurities exist inevitably in two-dimensional materials as they spontaneously adsorb onto the surface during fabrication, usually exerting detrimental effects on electronic transport. Here, we focus on a special type of impurities that preferentially adsorb onto the hollow regions of graphene nanoribbons (GNRs), and study how they affect the quantum transport in GNRs. Contrary to previous knowledge that random adatoms should localize electrons, the so-called Anderson localization, noteworthy quantized conductance peaks (QCPs) are observed at specific electron energies. These QCPs are remarkably robust against variations in system size, GNR edge, and adatom properties, and they can reappear at identical energies following an arithmetic sequence of device width. Further investigation of the wave function reveals a unique transport mode at each QCP energy which transmits through disordered GNRs reflectionlessly, while all the others become fully Anderson localized, indicating the survival of quantum ballistic transport in the localized regime. Our findings highlight the potential utility of hollow adatoms as a powerful tool to manipulate the conductivity of GNRs, and deepen the understanding of the interplay between impurities and graphene.

关键词： Transport phenomena Graphene Green's function methods Tight-binding model

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Piezovalley effect and magnetovalley coupling in altermagnetic semiconductors studied by first-principles calculations

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Physical Review B 2025年第13期111卷 134429-134429页

作者： Weifeng Xie Xiong Xu Yunliang Yue Huayan Xia Hui Wang School of Microelectronics and Physics Hunan University of Technology and Business Changsha 410205 China School of Physics Hunan Key Laboratory of Super Microstructure and Ultrafast Process Hunan Key Laboratory of Nanophotonics and Devices State Key Laboratory of Powder Metallurgy Central South University Changsha 410083 China College of Information Engineering Yangzhou University Yangzhou 225127 China

Clarifying the physical origin of valley polarization and exploring promising ferrovalley materials are conducive to the application of valley degrees of freedom in the field of information storage. Here, we explore two altermagnetic semiconductors (monolayers Nb2Se2O and Nb2SeTeO) with Néel temperature above room temperature based on first-principles calculations. We find that uniaxial strain induces valley polarization without spin-orbital coupling (SOC) in altermagnets owing to the piezovalley effect, while uniaxial compressive strain transforms the intrinsic ferrovalley semiconductor into a semimetal, half metal, and metal. Moreover, moderate biaxial compressive strain renders Janus monolayer Nb2SeTeO to robust Dirac-conelike band dispersion. The SOC and intrinsic in-plane magnetocrystalline anisotropy energy induce Dirac-conelike altermagnets to generate apparent valley polarization through magnetovalley coupling. In terms of SOC perturbation, we elucidate the physical mechanism behind in-plane magnetization-induced valley polarization and demonstrate that valley polarization is negatively correlated with the band gap. The present work reveals the physical origin of valley polarization in altermagnets and expands the application of ferrovalley at room temperature in valleytronics.

关键词： Degrees of freedom (mechanics)

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Regulation of magnon-phonon coupling by phonon angular momentum in two-dimensional systems

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Physical Review B 2023年第17期108卷 174426-174426页

作者： Qian Wang Shuang Liu Meng-Qiu Long Yun-Peng Wang Hunan Key Laboratory for Super-Microstructure and Ultrafast Process School of Physics Central South University 932 South Lushan Road Changsha 410000 People's Republic of China

The coupling between magnons and phonons modulates the transport properties of magnons, resulting in magnon polarons and magnon Seebeck effects, etc. Magnons possess well-defined angular momentum, while phonons are usually composed of linear atomic oscillations lacking angular momentum. However, in chiral systems, phonons become elliptical or circular; thus they will carry angular momentum. In this paper, we emphasize angular momentum and its role in the magnon-phonon coupling. Using a coupled-magnon-phonon model on the hexagonal lattice, we investigate the coupling of achiral and chiral phonons with three types of magnons, namely a magnon on one sublattice, ferromagnetic magnons, and antiferromagnetic magnons. We calculate the magnon-phonon dispersion relations and the strength of magnon-phonon coupling in the reciprocal space. We are particularly interested in the K and K′ points at the corner of the first Brillouin zone where the normal modes involve circular rotations of magnetization and displacement. We find a selective coupling wherein the coupling between magnons and phonons vanishes either when the magnitude of the magnon or phonon modes is zero or when the circular motion of magnetization is opposite to that of the displacements. These findings pave the way towards manipulating magnon polaron devices based on phonon angular momentum.

关键词： Magnons Spin-phonon coupling Chiral symmetry

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Pulse-area theorem for precision control of the rotational motions of a single molecule in a cavity

arXiv

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arXiv 2023年

作者： Fan, Li-Bao Shu, Chuan-Cun Hunan Key Laboratory of Nanophotonics and Devices Hunan Key Laboratory of Super-Microstructure and Ultrafast Process School of Physics Central South University Changsha410083 China

We perform a combined analytical and numerical investigation to explore how an analytically designed pulse can precisely control the rotational motions of a single-molecular polariton formed by the strong coupling of two low-lying rotational states with a single-mode cavity. To this end, we derive a pulse-area theorem that gives amplitude and phase conditions of the pulses in the frequency domain for driving the polariton from a given initial state to an arbitrary coherent state. The pulse-area theorem is examined for generating the maximum degree of orientation using a pair of pulses. We show that the phase condition can be satisfied by setting the initial phases of the two identically overlapped pulses or by controlling the time delay between pulses for practical applications. © 2023, CC BY.

关键词： Polariton

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Single-metal atoms supported on HfBO MBenes for efficient overall water splitting

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RSC Advances 2025年第24期15卷 19079-19087页

作者： Meiling Pan Xiuhua Cui Qun Jing Haiming Duan Fangping Ouyang Rong Wu Xinjiang Key Laboratory of Solid State Physics and Devices School of Physical Science and Technology Xinjiang University 777 Huarui Street Urumqi 830017 China School of Physics Hunan Key Laboratory for Super-Microstructure and Ultrafast Process Hunan Key Laboratory of Nanophotonics and Devices Central South University Changsha 410083 China

Two-dimensional hexagonal MBenes (h-MBenes), derived from h-MAB phases, exhibit great potential for electrochemical applications due to their unique electronic and catalytic properties. Using first-principles calculations, we explored single-atom transition metals (TMs) supported on h-MBene HfBO (TM@HfBO) as bifunctional catalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). TM@HfBO structures demonstrated excellent thermal stability and high electrical conductivity, making them suitable for electrocatalysis. For HER, Nb@HfBO showed outstanding activity with a near-ideal hydrogen adsorption free energy (ΔG_H = −0.01 eV), surpassing even platinum. For OER, ferromagnetic TM@HfBO systems (TM = Fe, Co, Ni) exhibited high catalytic potential, with Ni@HfBO achieving the lowest overpotential (η_OER = 0.48 V), outperforming IrO₂ (η_OER = 0.56 V). These results highlight TM@HfBO as a promising alternative to noble-metal-based catalysts. Our findings provide a foundation for designing cost-effective, high-performance electrocatalysts for overall water splitting and underscore the potential of HfBO-based materials in sustainable energy applications.

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Theoretical investigations on the magneto-Raman effect of CrI3

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Physical Review B 2023年第18期108卷 184414-184414页

作者： Shuang Liu Meng-Qiu Long Yun-Peng Wang School of Physics and Electronics Hunan Key Laboratory for Super-Microstructure and Ultrafast Process Central South University 932 South Lushan Road Changsha 410083 People's Republic of China

The magneto-optical property of magnets is used for detecting their magnetization and for information storage applications. The elastic interaction of light with magnetic materials is modulated by the spin-orbital coupling, which is manifested by the rotation of the polarization plane of scattered light with respect to the injected light. The magnetic order also participates in the inelastic Raman scattering of light, as experimentally demonstrated by an ∼40∘ rotation of the polarization plane by the two-dimensional ferromagnet CrI3. In this paper, we investigate the magneto-Raman properties of monolayer CrX3 (X=Cl, Br, and I) using first-principles methods. We calculate the Raman tensor and the Raman intensity due to the A1g phonon by taking the spin-orbit coupling into account. Experimental results on CrI3 are well reproduced. Both the rotation angle of the polarization plane of linearly polarized light and the Raman circular polarization strongly depend on the energy of the injected photons.

关键词： Magneto-optical effect Magnetic semiconductors Density functional calculations

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Polymer-Decorated 2D MoS2 Synaptic Transistors for Biological Bipolar Metaplasticities Emulation

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Chinese Physics Letters 2020年第8期37卷 177-188页

作者： Yuhang Zhao Biao Liu Junliang Yang Jun He Jie Jiang Hunan Key Laboratory of Super Microstructure and Ultrafast Process School of Physics and ElectronicsCentral South UniversityChangsha 410083China

Biological bipolar metaplasticities were successfully mimicked in two-dimensional(2D)MoS2 transistors via the implementation of two different MoS2 surface decorations,poly(vinyl alcohol)(PVA)and chitosan ***,the depressing metaplasticity was successfully mimicked when the PVA bio-polymer was used as the surface decoration layer,whereas the metaplasticity of long-term potentiation was realized when the chitosan bio-polymer was taken as the surface decoration ***,the electronic band structures of the 2D MoS2 devices with different surface decorations were further investigated using first-principles calculations for understanding the underlying mechanisms of such bipolar *** results will deepen our understanding of metaplasticity,and have great potential in neuromorphic computing applications.

关键词： MoS2 poly(vinyl plasticity

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Highly stretchable polymer/silver nanowires composite sensor for human health monitoring

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Nano Research 2020年第4期13卷 919-926页

作者： Yanjing Zhang Pei He Meng Luo Xiaowen Xu Guozhang Dai Junliang Yang Hunan Key Laboratory for Super-microstructure and Ultrafast Process School of Physics and ElectronicsCentral South UniversityChangsha 410083China

Flexible strain sensors exhibit outstanding advantages in terms of sensitivity and stability by detecting changes in physical *** can be easily attached to human skin and clothed to achieve monitoring of human motion and ***,general sensing material shows low stretchability and cannot respond to signals under large *** this work,a highly stretchable polymer composite was developed by adding small amount(0.17 wt.%)of silver nanowires(AgNWs)in stretchable conductive polymer *** conductivity of polymer/AgNWs composite is 1.3 S/m with the stretchability up to 500%.The stretchable strain sensor based on the polymer/AgNWs composite can respond to strain signals in real time,even for 1%strain response,and shows excellent stability over 1,000 loading/unloading ***,the strain sensor can be attached to human skin and clothed to monitor joints,throat and pulse of the human *** human body electrocardiogram(ECG)signal was detected successfully with the polymer/AgNWs electrode,which is comparable to the signal obtained by the commercial ***,the sensors enable monitoring of human movement and *** advantages make it a potential application in wearable devices and electronic skin.

关键词： stretchable sensor silver nanowires health monitoring electrocardiogram

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Quantum Speed Limit under Brachistochrone Evolution

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Physical Review Applied 2023年第1期20卷 014031-014031页

作者： Fu-Quan Dou Min-Peng Han Chuan-Cun Shu College of Physics and Electronic Engineering Northwest Normal University Lanzhou 730070 China Hunan Key Laboratory of Nanophotonics and Devices Hunan Key Laboratory of Super-Microstructure and Ultrafast Process School of Physics Central South University Changsha 410083 China

According to the Heisenberg uncertainty principle between time and energy fluctuation, a concept of the quantum speed limit (QSL) has been established to determine the minimum evolutionary time between quantum states. Considerable theoretical and experimental efforts are invested in obtaining the QSL time bounds in various scenarios. However, it remains a long-standing goal to derive a meaningful QSL bound for a general quantum problem. Here, we propose a geometrical approach to derive a QSL bound for closed and open quantum systems. By solving a quantum brachistochrone problem in the framework of the Riemannian metric, we show that the QSL between a given initial state and a final state is determined not only by the entire dynamics of the system but also by the individual dynamics of a critical parameter. We exemplify the utility of the bound in three representative scenarios, demonstrating a pronounced advantage in finding a tight and meaningful QSL bound of a general quantum evolution problem.

关键词： Cold atoms & matter waves Quantum control Quantum foundations Quantum state transfer Quantum transport Tunneling & traversal time Chaos & nonlinear dynamics Two-level models

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Maximizing orientation of a three-state molecule in a cavity with analytically designed pulses

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Physical Review A 2025年第3期111卷 033119-033119页

作者： Li-Bao Fan Hai-Ji Li Qi Chen Hang Zhou Heng Liu Chuan-Cun Shu Hunan Key Laboratory of Nanophotonics and Devices Hunan Key Laboratory of Super-Microstructure and Ultrafast Process School of Physics Central South University Changsha 410083 China Hunan Provincial Key Laboratory of Flexible Electronic Materials Genome Engineering School of Physics and Electronic Science Changsha University of Science and Technology Changsha 410114 China

We theoretically explore the precise control of a molecular polariton by strongly coupling the lowest three rotational states of a single molecule with a single-mode cavity. We examine two distinct cavity resonance configurations: a fundamental frequency cavity (ωc=2B with the rotational constant B) resonating with the lowest two rotational states, and a second harmonic cavity (ωc=4B) coupling with the first and second excited rotational states. We propose two control schemes based on the two polariton configurations and derive the corresponding pulse-area theorems to achieve a theoretical maximum orientation of 0.7746, identical to the molecule without the cavity. The control schemes are analyzed in carbonyl sulfide (OCS) molecules in their ground rotational state. Our numerical simulation results demonstrate the theoretical control schemes and analyze the sensitivity of the molecular polariton orientation degree to the control field bandwidth and phases. This work provides a valuable reference for achieving maximum field-free orientation of ultracold three-state molecules in a cavity using analytically designed pulses.

关键词： Molecular polarity

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