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Frustration-enhanced persistent currents in correlated trimer nanorings

Physical Review B 2025年第8期111卷 L081117-L081117页

作者： Tie-Feng Fang Wei-Tao Lu Ai-Min Guo Qing-Feng Sun School of Physical Science and Technology Nantong University Nantong 226019 China Hunan Key Laboratory for Super-microstructure and Ultrafast Process School of Physics and Electronics Central South University Changsha 410083 China International Center for Quantum Materials School of Physics Peking University Beijing 100871 China Hefei National Laboratory Hefei 230088 China

We investigate the persistent current in a correlated trimer nanoring comprising three magnetic atoms, which sits on a metallic host and encloses a magnetic flux. In the molecular-orbital regime, charge fluctuations can reverse the aromaticity of the trimer molecule by driving quantum phase transitions between many-body states. It is shown that in frustrated trimers the superexchange-induced current as a function of interatom hopping is enhanced by the competition of conflicting magnetic orders, with an asymmetric peak at the quantum criticality separating the ferromagnetic and antiferromagnetic Kondo regimes. Interestingly, the critical current undergoes an anomalous rise with temperature before decaying, signaling the suppression of the Kondo bound state at finite temperature. Our results demonstrate that the coherent current response to external flux indeed conveys important information on the states of strongly correlated systems.

关键词： Nanorings

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Channel-resolved photoionization time delay of hydrogen atoms in two-color ultraviolet laser fields

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Optics Express 2025年第7期33卷 15044-15056页

作者： Gao, Xuan-Hong Jing, Wen-Quan Du, Jin-Xu Jiao, Zhi-Hong Wang, Guo-Li Zhao, Song-Feng College of Physics and Electronic Engineering Northwest Normal University Key Laboratory of Atomic and Molecular Physics and Functional Materials of Gansu Province Lanzhou730070 China Laboratory of Super-Microstructure and Ultrafast Process School of Physics Central South University Changsha410083 China

We investigate theoretically the phase-dependent photoelectron spectra in resonance-enhanced multiphoton ionization (REMPI) of hydrogen atoms with 200-400-nm ultraviolet laser fields by solving the time-dependent Schrödinger equation. Unlike photoionization time delay in the REMPI of Ne and Ar driven by 400-800-nm laser fields, several Rydberg states are involved [Phys. Rev. A 98, 013409 (2018);Phys. Rev. A 109, 013103 (2024)]. Here we show that the electron can be released to the continuum state by absorbing three 200-nm photons (i.e., non-resonant channel) or firstly excited to one Rydberg state (i.e., the 3d state) through a two-photon transition and then removed by absorbing another 200-nm photon (i.e., resonant channel). The channel-resolved time delays of the above-threshold ionization (ATI) and sideband (SB) peaks are extracted from the phase-dependent photoelectron spectra. We find that a relative time delay about +165 attoseconds exists between the first resonant SB and non-resonant SB. The phase shifts of the high-energy electrons in these two channels are affected by the continuum-continuum (CC) transitions and the centrifugal barrier effect. Additionally, the intensities of the pump and probe fields affect the phase shifts of high-energy electrons in the non-resonant and resonant channels, respectively. This study demonstrates the possibility of higher-order transitions in ATI of hydrogen atoms at higher laser intensities and offers a theoretical insight for understanding the channel-resolved time delays in atomic REMPI processes. © 2025 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement.

关键词： Rydberg states

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Precise quantum control of molecular rotation toward a desired orientation

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Physical Review Research 2025年第1期7卷 L012049-L012049页

作者： Qian-Qian Hong Daoyi Dong Niels E. Henriksen Franco Nori Jun He 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 Australian Artificial Intelligence Institute Faculty of Engineering and Information Technology University of Technology Sydney NSW 2007 Australia Department of Chemistry Technical University of Denmark Building 207 DK-2800 Kongens Lyngby Denmark Quantum Computing Center and Theoretical Quantum Physics Laboratory RIKEN Saitama 351-0198 Japan Physics Department University of Michigan Ann Arbor Michigan 48109 USA

The lack of a direct map between control fields and desired control objectives poses a significant challenge in applying quantum control theory to quantum technologies. Here, we propose an analytical framework to precisely control a limited set of quantum states and construct desired coherent superpositions using a well-designed laser pulse sequence with optimal amplitudes, phases, and delays. This theoretical framework that corresponds to a multilevel pulse-area theorem establishes a straightforward mapping between the control parameters of the pulse sequence and the amplitudes and phases of rotational states within a specific subspace. As an example, we utilize this approach to generate 15 distinct and desired rotational superpositions of ultracold polar molecules, leading to 15 desired field-free molecular orientations. By optimizing the superposition of the lowest 16 rotational states, we demonstrate that this approach can achieve a maximum orientation value of |〈cosθ〉|max above 0.99, which is very close to the global optimal value of 1 that could be achieved in an infinite-dimensional state space. This work marks a significant advancement in achieving precise control over multilevel subsystems within molecules. It holds potential applications in molecular alignment and orientation, as well as in various interdisciplinary fields related to the precise quantum control of ultracold polar molecules, opening up considerable opportunities in molecular-based quantum techniques.

关键词： Molecular orientation

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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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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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Dynamical theory of chiral-induced spin selectivity in electron donor–chiral molecule–acceptor systems

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Physical Review B 2025年第20期111卷 205417-205417页

作者： Tian-Yi Zhang Yue Mao Ai-Min Guo Qing-Feng Sun International Center for Quantum Materials School of Physics Peking University Beijing 100871 China Hunan Key Laboratory for Super-microstructure and Ultrafast Process School of Physics Central South University Changsha 410083 China Hefei National Laboratory Hefei 230088 China

The chiral-induced spin selectivity (CISS) effect, a phenomenon where the chirality of molecules imparts significant spin selectivity to electron transfer processes, has garnered increasing interest among the chemistry, biology, and physics communities. Although this effect was discovered more than a decade ago, the dynamical process of how electron spin polarization is caused by chiral molecules is still unclear. Here, we propose a dynamical theory of electron transfer in donor-chiral molecule bridge-acceptor systems without electrodes or substrates based on the Lindblad-type master equation. We demonstrate that the molecular spin-orbit coupling generates unequal spin velocities and achieves steady spin polarization with the help of dephasing. Our work elucidates the dynamical process of CISS and may promote the applications of chiral-based spintronic devices.

关键词： Spin orbit coupling

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Confined subdiffusion in three dimensions

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Chinese Physics B 2014年第11期23卷 145-151页

作者：覃善林何勇 Hunan Key Laboratory for Super-microstructure and Ultrafast Process Institute of Super Microstructure and Ultrafast Process in Advanced MaterialsSchool of Physics and Electronics Central South University

Three-dimensional （3D） Fick＇s diffusion equation and fractional diffusion equation are solved for different reflecting boundaries. We use the continuous time random walk model （CTRW） to investigate the time-averaged mean square dis- placement （MSD） of a 3D single particle trajectory. Theoretical results show that the ensemble average of the time-averaged MSD can be expressed analytically by a Mittag-Leffler function. Our new expression is in agreement with previous formu- las in two limiting cases：（^-δ2） ~ △1 in short lag time and （^-δ2} ~ △1 -α in long lag time. We also simulate the experimental data of mRNA diffusion in living E. coli using a 3D CTRW model under confined and crowded conditions. The simulation results are well consistent with experimental results. The calculations of power spectral density （PSD） further indicate the subdiffsive behavior of an individual trajectory.

关键词： confined subdiffusion three dimensions time-averaged mean squared displacement

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Low-temperature-cured highly conductive composite of Ag nanowires & polyvinyl alcohol

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Chinese Physics B 2017年第7期26卷 426-432页

作者：何松张祥杨兵初徐晓梅陈辉周聪华 Hunan Key Laboratory of Super-microstructure and Ultrafast Process School of Physics and ElectronicsCentral South University

Flexible conductive films were fabricated from a low-temperature-cured, highly conductive composite of silver nanowires （as conducting filler） and polyvinyl alcohol （PVA, as binder）. Sheet resistance of 0.12 Ω/sq, conductivity of 2.63 ×10^4 S/cm, and contact resistance of 1.0Ω/cm^2 were measured in the films, along with excellent resistance to scratch- ing and good flexibility, making them suitable electrical contact materials for flexible optoelectronic devices. Effects of curing temperature, curing duration, film thickness, and nanowire length on the film＇s electrical properties were studied. Due to the abundance of hydroxyl groups on its molecular chains, the addition of PVA improves the film＇s flexibility and resistance to scratching. Increased nanowire density and nanowire length benefit film conductance. Monte Carlo simulation was used to further explore the impact of these two parameters on the conductivity. It was observed that longer nanowires produce a higher length-ratio of conducting routes in the networks, giving better film conductivity.

关键词： conductive composite polyvinyl alcohol silver nanowires Monte Carlo simulation

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Cascaded plasmonic nanorod antenna for large broadband local electric field enhancement

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Chinese Physics B 2019年第10期28卷 535-540页

作者： Dou Zhang Zhong-Jian Yang Jun He Hunan Key Laboratory of Super Microstructure and Ultrafast Process School of Physics and ElectronicsCentral South University

We propose a cascaded plasmonic nanorod antenna for large broadband electric near-field enhancement. The structure has one big gold nanorod on each side of a small two-wire antenna which consists of two small gold nanorods. For each small nanorod, the enhanced and broadened optical response can be obtained due to the efficient energy transfer from its adjacent big nanorod through strong plasmonic near-field coupling. Thus, the electric field intensity of the cascaded antenna is significantly larger and broader than that of the individual small two-wire antenna. The resonant position, field intensity enhancement, and spectral width of the cascaded antenna are highly tunable by varying the geometry of the system. The quantum efficiency of the cascaded antenna is also greatly enhanced compared with that of the small antenna. Our results are important for the applications in field-enhanced spectroscopy.

关键词： surface plasmon optical antenna electric field enhancement broadband cascaded

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Plasmon-assisted channel-tunable bistable states in a monolayer MoS2 nanoresonator coupled to a metallic nanoshell

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Optics Express 2025年第11期33卷 23568-23578页

作者： Jian-Bo Li Hong-Mei Gong Yu-Xiang Peng Si Xiao Jin-Bo Hu Lin-Wen Long Department of Physics Hunan Province Key Laboratory of Materials Surface & Interface Science and Technology Central South University of Forestry and Technology Changsha 410004 China jbli_opt@*** jbli_opt@*** School of Optical and Electronic Information & Jiangsu/Suzhou Key Laboratory of Biophotonics & International Joint Metacenter for Advanced Photonics and Electronics Suzhou City University Suzhou 215104 China hmgong@*** School of Physics Hunan Key Laboratory of Super microstructure and Ultrafast Process Central South University Changsha 410083 China sixiao@*** College of Materials and Energy Central South University of Forestry and Technology Changsha 410004 China

We study how to obtain the channel-tunable bistable states in a coupled system consisting of a monolayer MoS 2 nanomechanical resonator (NR) and a metallic nanoshell (MNS) beyond the dipole approximation. The MNS is constructed by a metallic core and a dielectric shell. The calculated results show that the linear absorption spectrum exhibits some new features, such as three-phonon resonance, Rayleigh resonance, and ac-Stark resonance. In a strong exciton-plasmon coupling regime, the absorption peak and amplification peak in the absorption spectrum can be greatly enhanced by adjusting the exciton-phonon coupling strength. Especially, we plot the bistability phase diagrams in the system’s parameter space and highlight the strong dependency of the lower (upper) bistable threshold on the pumping intensity, the MNS-NR distance, and the dielectric shell thickness. The ratio of linear absorption in the upper and lower stable states can reach 42. For a given MNS with a fixed shell thickness, it is easy to achieve single-channel or dual-channel bistable states by only adjusting the exciton-phonon coupling strength via modulation of the length of the MoS 2 nanosheet along the NR axis. The findings obtained here are very useful for extensive applications such as optical memory cells and channel-tunable bistable switches.

关键词： Absorption spectroscopy Light propagation Metal nanoparticles Nonlinear absorption Optical properties Slow light

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