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Janus monolayer TaNF:A new ferrovalley material with large valley splitting and tunable magnetic properties

Frontiers of physics 2023年第5期18卷 173-181页

作者：郑贵博蘧水仙周文哲欧阳方平 School of Physics and Electronics and Hunan Key Laboratory for Super-Microstructure and Ultrafast Processand Hunan Key Laboratory of Nanophotonics and DevicesCentral South UniversityChangsha 410083China School of Physics and Technology Xinjiang UniversityUrumqi 830046China State Key Laboratory of Powder Metallurgy and Powder Metallurgy Research InstituteCentral South UniversityChangsha 410083China

Materials with large intrinsic valley splitting and high Curie temperature are a huge advantage for studying valleytronics and practical *** this work,using first-principles calculations,a new Janus TaNF monolayer is predicted to exhibit excellent piezoelectric properties and intrinsic valley splitting,resulting from the spontaneous spin polarization,the spatial inversion symmetry breaking and strong spin-orbit coupling(SOC).TaNF is also a potential two-dimensional(2D)magnetic material due to its high Curie temperature and large magnetic anisotropy *** effective control of the band gap of TaNF can be achieved by biaxial strain,which can transform TaNF monolayer from semiconductor to *** magnitude of valley splitting at the CBM can be effectively tuned by biaxial strain due to the changes of orbital composition at the *** magnetic anisotropy energy(MAE)can be manipulated by changing the energy and occupation(unoccupation)states of d orbital compositions through biaxial *** addition,Curie temperature reaches 373 K under only−3%biaxial strain,indicating that Janus TaNF monolayer can be used at high temperatures for spintronic and valleytronic devices.

关键词： Janus valley splitting Curie temperature magnetic anisotropy energy first-principles calculations

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Frustration-enhanced persistent currents in correlated trimer nanorings

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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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Epitaxial quasi-2D/3D hybrid perovskite heterojunctions for photodetector with enhanced detectivity and stability

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Nano Research 2024年第7期17卷 6594-6602页

作者： Yifu Chen Lin Zhang Xinxin Peng Weiran Qin Shiqing Li Yingwei Wang Zhihui Chen Si Xiao Bin Yang Biao Liu Junliang Yang Han Huang Yun Lin Jun He Liming Ding Yongbo Yuan Hunan Key Laboratory of Super Microstructure and Ultrafast Process School of PhysicsCentral South UniversityChangsha 410083China Hunan Key Laboratory of Nanophotonics and Devices School of PhysicsCentral South UniversityChangsha 410083China College of Materials Science and Engineering Hunan UniversityChangsha 410082China Department of Photoelectric Information School of PhysicsCentral South UniversityChangsha 410083China Center for Excellence in Nanoscience Key Laboratory of Nanosystem and Hierarchical FabricationNational Center for Nanoscience and TechnologyChinese Academy of ScienceBeijing 100190China

Although numerous metal halide perovskite materials have been investigated in the field of optoelectronic,the development of perovskite heterojunctions with exotic structures is still ***,we report the epitaxial growth of quasi-two-dimensional(Q-2D)perovskites on methylammonium lead iodide(MAPbI_(3))single crystals to form perovskite heterojunctions with interfacial *** MAPbI_(3)adjacent to epitaxial Q-2D perovskite shows blue shifted photoluminescence with shortened lifetime,which becomes significant with the reduced layer number of the Q-2D *** findings suggest the presence of an interfacial strain gradient leading to enhanced photocarrier ***,compared to the MAPbI_(3)single crystal detector,the BA_(2)MAPb_(2)I_(7)/MAPbI_(3)(BA:n-butylamine)heterojunction-based photodetector demonstrates a bandpass detecting property and exhibits 5 times enhanced external quantum efficiency and 83 times enhanced specific detectivity(D*=3.26×10^(11)Jones).Remarkably,the unencapsulated BA_(2)MAPb_(2)I_(7)/MAPbI_(3)heterojunction is stable in ambient condition for>300 *** Q-2D/3D heterojunction shows suppressed ion inter-diffusion due to the presence of Q-2D phase.

关键词： epitaxial growth interfacial strain quasi-two-dimensional/three-dimensional(Q-2D/3D)heterojunctions ion inter-diffusion

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Anisotropic Rabi model with two-photon relaxation

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Physical Review A 2024年第2期110卷 023708-023708页

作者： Hui Li Jia-Kai Shi Li-Bao Fan Zi-Min Li Chuan-Cun Shu Institute of Quantum Physics Hunan Key Laboratory of Nanophotonics and Devices Hunan Key Laboratory of Super-Microstructure and Ultrafast Process School of Physics Central South University

The interplay of three light-matter interaction processes, i.e., rotating and counterrotating interactions and two-photon relaxation of the light field, is a topic of interest in quantum optics and quantum information processing. In this work we investigate theoretically the three light-matter interaction processes using the anisotropic Rabi model, which accounts for different strengths of rotating and counterrotating interactions and the unique occurrence of photon escape exclusively in pairs. By numerically solving the Lindblad master equation, we analyze the excitation-relaxation dynamics and derive a non-Hermitian effective Hamiltonian to gain further physical insights. To explore the individual effects of these interactions, we examine three analytically tractable limits of the effective Hamiltonian. Our analysis reveals that the three competitive light-matter interaction processes exhibit sensitivity to parity, leading to intriguing phenomena in both transient and steady states. Particularly interesting dynamical patterns resembling quantum phase transitions emerge when these three interaction terms compete. This work deepens the understanding of ultrastrong light-matter interaction in open quantum systems and offers valuable insights into cavity-based quantum computations.

关键词： Quantum description of light-matter interaction Non-Hermitian systems Rabi model

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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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General approach for efficient prediction of refrigeration performance in caloric materials

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Physical Review Applied 2024年第1期22卷 014036-014036页

作者： Xiong Xu Weifeng Xie Fangbiao Li Chang Niu Min Li Hui Wang 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

Solid-state refrigeration holds promise for environmentally friendly cooling with high energy efficiency and downsize scalability. However, its refrigeration performance is notably inferior in comparison with commercial refrigerants due to the lack of scientific guidance for material discovery and performance improvement. Here, we provide an efficient approach to investigate caloric effect under external factors (i.e., electric fields, magnetic fields, and mechanical fields). Using the electrocaloric material PbTiO3 (PTO) as a prototype and employing ab initio calculations combined with deep potential machine learning, we demonstrate the field-dependent isothermal entropy change ΔS and adiabatic temperature change ΔT, along with the coefficient of performance near the phase transitions temperature (Tc). Through analysis of the evolution of microscopic dynamics, we clarify that the refrigeration process involves heat absorption by a transition from a low-potential-energy to a high-potential-energy state. This transition, in a more general case, can be defined as a conventional caloric effect driven by temperature when T > Tc, or an inverse caloric effect driven by external field when T Tc. Importantly, this approach is successfully applied to magnetocaloric, elastocaloric, and barocaloric materials, from which we further showcase the regulation of caloric effect in multicaloric refrigeration process. This work establishes an effective and universal method for predicting key refrigeration parameters, which can be applied to extensive caloric materials, that provide important insights for material design in solid-state cooling technology.

关键词： Elastocaloric effect Electrocaloric effect Magnetocaloric effect Order parameters Solid-state refrigeration Ab initio molecular dynamics Deep learning Density functional calculations

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High-performance 1D CsPbBr_(3)/CdS photodetectors

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Rare Metals 2024年第11期43卷 5932-5942页

作者： Zhi-Lin Xiang Qiu-Hong Tan Ting Zhu Pei-Zhi Yang Yan-Ping Liu Ying-Kai Liu Qian-Jin Wang College of Physics and Electronic Information Yunnan Normal UniversityKunming 650500China Yunnan Provincial Key Laboratory for Photoelectric Information Technology Yunnan Normal UniversityKunming 650500China Key Laboratory of Advanced Technique&Preparation for Renewable Energy Materials Ministry of EducationYunnan Normal UniversityKunming 650500China Hunan Key Laboratory for Super-Microstructure and Ultrafast Process School of Physics and ElectronicsCentral South UniversityChangsha 410083China

The emergence of all-inorganic perovskite CsPbBr_(3)has ignited significant interest in optoelectronic devices,However,CsPbBr_(3)thin film-based photodetectors face performance limitations due to grain boundaries and defect *** address these challenges,we introduce a novel typeⅡheterojunction photodetector utilizing CsPbBr_(3)micro wires(MWs)and CdS nanoribbons(NBs).Remarkably,this photodetector exhibits exceptional characteristics:a high on/off current ratio(1.07×10^(5)),a responsivity of up to 1.35×10^(4)A·W^(-1),specific detectivity of 5.94×10^(15)Jones,external quantum efficiency of2.83×10^(4)%and rapid response/recovery time(400μs/3 ms).These superior performances stem from the exceptional crystalline quality of CsPbBr_(3)MWs and CdS NBs,coupled with the establishment of a typeⅡband alignment at their *** configuration enables efficient carrier separation while suppressing ***,1D CsPbBr_(3)MW/CdS NB heterojunction photodetectors demonstrate reliable imaging capabilities under visible light *** findings present an innovative solution for high-performance perovskite-based photodetectors,holding promise for future commercial applications.

关键词： All-inorganic perovskite Photodetectors Interface coupling Electric charge transfer

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Intrinsically ultralow lattice thermal conductivity and giant thermoelectric effect in Ag-based intercalated layered crystalline solids

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Physical Review B 2024年第23期109卷 235202-235202页

作者： Junpeng Yuan Min Li Hui Wang 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

Understanding the nature of low thermal conductivity and phonon transport properties is critical for the design of potential thermoelectric materials. Based on density-functional theory combined with the phonon Peierls-Boltzmann transport equation, we reveal that Ag-based intercalated layered materials AgBiX2 (X = S, Se, and Te) have inherently low lattice thermal conductivity, which is mainly attributed to the anticrossing behavior of low-frequency optical phonons and longitudinal acoustic phonons induced by the rattling mode of the cations. It is found that the optical phonons in AgBiS2 contribute dominantly (up to 65%) to the total thermal conductivity, originating from the weak bonding nature of intercalated Ag atoms that leads to strong anharmonicity and softening of transverse acoustic phonons. Electronic relaxation times under acoustic deformation potential scattering, polar optical phonon scattering, and ionized impurity scattering are considered to obtain reasonable electron transport properties. The ZT value of p-type AgBiS2 reaches 1.77 for optimal doping at room temperature, which can further be enhanced to ∼2.6 through strain engineering. The present work demonstrates that chemically controlled weak bonding in Ag-based intercalated layered structure produces intrinsically low thermal conductivity and provides important theoretical insight for thermal insulator and thermoelectric applications.

关键词： Anharmonic lattice dynamics Electrical conductivity Electron-phonon coupling Electronic structure Phonons Scattering theory Seebeck effect Thermal conductivity Thermoelectric effects Thermoelectrics 3-dimensional systems Layered crystals Ab initio molecular dynamics Boltzmann theory Density functional calculations Density functional theory First-principles calculations

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Enhanced thermodynamic stability and carrier lifetime in BF4-doped wide-band-gap perovskite solar cells

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Physical Review B 2024年第4期110卷 045142-045142页

作者： Zhong-Yuan Wang Kai-Feng Wang Jun-Jie Jin Fangping Ouyang Biao Meng Zhaofeng Wu Li-Min Liu Chuan-Jia Tong Institute of Quantum Physics Hunan Key Laboratory of Nanophotonics and Devices Hunan Key Laboratory of Super-Microstructure and Ultrafast Process School of Physics School of Material Science and Engineering School of Physics

Recent experiments show that doping a small amount of fluorinated pseudohalides (BF4) into CH3NH3PbI3 (MAPbI3) can enhance the performance of wide-band-gap (WBG) perovskite solar cells. Using time-domain density functional theory and ab initio nonadiabatic molecular dynamics we demonstrate that BF4-doped WBG perovskites not only maintain the high defect tolerance but also exhibit greatly improved thermodynamic stability due to enhanced dissociation energy and reduced thermal atomic fluctuation. The strengthened hydrogen bond network introduces increased lattice rigidity, confined inner space, and the reorientated dipole direction of methylammonium molecules, which synergistically suppress the ion migration in BF4-doped MAPbI3 perovskite. Notably, the charge carrier lifetime experiences an order-of-magnitude improvement after BF4 doping, which is mainly attributed to the weakened nonadiabatic coupling. This work provides valuable insights into the effect of fluorinated pseudohalides doped in perovskite materials and suggests a promising approach to enhancing the stability and efficiency of WBG perovskite solar cells.

关键词： Carrier dynamics Electron-phonon coupling Organic-inorganic hybrid perovskites Photovoltaic absorbers Density functional calculations Molecular dynamics

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Giant reversible electrocaloric effect in monolayer group-IV monochalcogenides

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Physical Review B 2024年第6期110卷 064103页

作者： Xiong Xu Min Li X. Lin Hui Wang 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

Monolayer electrocaloric (EC) materials have emerged as promising candidates to achieve economic and green solid-state refrigeration, especially in micro- or nanoscale chip cooling in the post-Moore law period. In this paper, we trained a machine-learning-based deep potential (DP) model of monolayer group-IV monochalcogenides MXs (M = Ge, Sn; X = S, Se) with a database from first-principles calculations, which incorporates the accuracy of ab initio molecular dynamics and efficiency of classical method. The DP model was further applied to study the EC effect (ECE) in monolayer MXs by simulating the temperature-driven phase transitions and electric polarization dynamics under different external electric fields. The results indicate MXs featuring giant reversible isothermal entropy change (ΔS) and adiabatic temperature change (ΔT) near their order-disorder phase transition. Particularly, for E = 100 MV/m, |ΔS| = 68 J/(kg K) and |ΔT| = 75 K are obtained for GeS, which individually rival the state-of-the-art ECE figures of merit, surpassing most other ferroelectric materials, particularly the two-dimensional (2D) CuInPS and strained SrTiO3 films. Furthermore, electric field shifts of the order of 10 MV/m yield huge reversible EC strengths of ΔS/ΔE = 5.4 Jmkg−1K−1MV−1 and ΔT/ΔE = 6 KmMV−1. The origin of the giant ECE in MXs was explained through macroscopic thermodynamic ratios, phenomenological Landau theory, and microscopic phonon vibration analysis. Interestingly, the entropy change can be approximated to be proportional to the square of the polarization change (ΔP2), and the application of electric field shifts the low-frequency phonons to the higher-frequency range, with the M atom contributing more to the entropy change than the X atom. In this paper, we provide important insights for exploration and design of 2D EC materials in future practical applications.

关键词： Electrocaloric effect Entropy Solid-state refrigeration 2-dimensional systems Ferroelectrics Ab initio molecular dynamics Machine learning

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