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Creation and manipulation of higher-order topological states by altermagnets

Physical Review B 2024年第20期109卷 L201109-L201109页

作者： Yu-Xuan Li Yichen Liu Cheng-Cheng Liu Center for Quantum Physics Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement MOE School of Physics Beijing Institute of Technology Beijing 100081 China

We propose to implement tunable higher-order topological states in a heterojunction consisting of a two-dimensional (2D) topological insulator and the recently discovered altermagnets, whose unique spin-polarization in both real and reciprocal space and null magnetization are in contrast to conventional ferromagnets and antiferromagnets. Based on symmetry analysis and effective edge theory, we show that the special spin splitting in altermagnets with different symmetries, such as d wave, can introduce Dirac mass terms with opposite signs on the adjacent boundaries of the topological insulator, resulting in the higher-order topological state with mass-domain-bound corner states. Moreover, by adjusting the direction of the Néel vector, we can manipulate such topological corner states by moving their positions. By first-principles calculations, taking a 2D topological insulator bismuthene with a square lattice on an altermagnet MnF2 as an example, we demonstrate the feasibility of creating and manipulating the higher-order topological states through altermagnets. Finally, we discuss the experimental implementation and detection of the tunable topological corner states, as well as the potential non-Abelian braiding of the Dirac corner fermions.

关键词： First-principles calculations Topological materials

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Twisted Magnetic Van der Waals Bilayers: An Ideal Platform for Altermagnetism

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Physical Review Letters 2024年第20期133卷 206702-206702页

作者： Yichen Liu Junxi Yu Centre for Quantum Physics Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement (MOE) School of Physics Beijing Institute of Technology Beijing 100081 China

We introduce a universal methodology for generating and manipulating altermagnetism in two-dimensional (2D) magnetic Van der Waals (MvdW) materials through twisting. We find that a key in-plane twofold rotational operation can be achieved in a twisted bilayer of any 2D MvdW material, which takes one of all five 2D Bravais lattices, thereby inducing altermagnetism. By choosing the constituent MvdW monolayer with specific symmetry, our approach can tailor altermagnetism of any type, such as d wave, g wave, and i wave. Furthermore, the properties of our twisted altermagnetic materials can be easily engineered. Taking a transition-metal oxyhalide VOBr as an example, we find that by tuning the twist angle and Fermi level, a giant spin Hall angle can be obtained, much larger than the experimentally reported. This approach establishes a general, robust, and adjustable platform to explore altermagnetism and provides a new efficient way to generate and manipulate the spin current.

关键词： Magnetism 2-dimensional systems Altermagnets Van der Waals systems Density functional theory Linear response theory Tight-binding model Wannier function methods

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Fabry-Perot superconducting diode

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Physical Review B 2024年第18期109卷 184513-184513页

作者： Xian-Peng Zhang Centre for Quantum Physics Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement (MOE) School of Physics Beijing Institute of Technology Beijing 100081 China

Superconducting diode effects (SDEs) occur in systems with asymmetric critical supercurrents |I+c|≠|I−c| yielding dissipationless flow in one direction (e.g., +), while dissipative transport in the opposite direction (−). Here we investigate the SDE in a phase-biased ϕ Josephson junction with a double-barrier resonant-tunneling InAs nanowire nested between proximitized InAs/Al leads with finite momentum ℏq Cooper pairing. Within the Bogoliubov-de Gennes (BdG) approach, we obtain the exact BCS ground state energy EG(q,ϕ) and I+c≠|I−c| from the current-phase relation IG(q,ϕ)∼∂ϕEG(q,ϕ). The SDE arises from the accrued Andreev phase shifts δϕL,R(q,ϕ) leading to asymmetric BdG spectra for q≠0. Remarkably, the diode efficiency γ=(I+c−|I−c|)/(I+c+|I−c|) shows multiple Fabry-Perot resonances γ≃26% at the double-barrier Andreev bound states as the well depth Vg is varied. Our γ also features sign reversals for increasing q and high sensitiveness to fermion-parity transitions. The latter enables I+c(ϕ+)⇄I−c(ϕ−) switchings over narrow phase windows, i.e., ϕ+,ϕ−∈Δϕ≪π, possibly relevant for future superconducting electronics.

关键词： Andreev reflection Josephson effect Diodes Nanowires quantum dots Superconductors Bogoliubov-de Gennes equations Green's function methods

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Absence of E2g Nematic Instability and Dominant A1g Response in the Kagome Metal CsV3Sb5

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Physical Review X 2024年第3期14卷 031015-031015页

作者： Zhaoyu Liu Yue Shi Qianni Jiang Elliott W. Rosenberg Jonathan M. DeStefano Jinjin Liu Chaowei Hu Yuzhou Zhao Zhiwei Wang Yugui Yao David Graf Pengcheng Dai Jihui Yang Xiaodong Xu Jiun-Haw Chu Department of Physics Department of Materials Science and Engineering Centre for Quantum Physics Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement (MOE) School of Physics Beijing Key Lab of Nanophotonics and Ultrafine Optoelectronic Systems Department of Physics and Astronomy

Ever since the discovery of the charge density wave (CDW) transition in the kagome metal CsV3Sb5, the nature of its symmetry breaking has been under intense debate. While evidence suggests that the rotational symmetry is already broken at the CDW transition temperature (TCDW), an additional electronic nematic instability well below TCDW has been reported based on the diverging elastoresistivity coefficient in the anisotropic channel (mE2g). Verifying the existence of a nematic transition below TCDW is not only critical for establishing the correct description of the CDW order parameter, but also important for understanding low-temperature superconductivity. Here, we report elastoresistivity measurements of CsV3Sb5 using three different techniques probing both isotropic and anisotropic symmetry channels. Contrary to previous reports, we find the anisotropic elastoresistivity coefficient mE2g is temperature independent, except for a step jump at TCDW. The absence of nematic fluctuations is further substantiated by measurements of the elastocaloric effect, which show no enhancement associated with nematic susceptibility. On the other hand, the symmetric elastoresistivity coefficient mA1g increases below TCDW, reaching a peak value of 90 at T*=20 K. Our results strongly indicate that the phase transition at T* is not nematic in nature and the previously reported diverging elastoresistivity is due to the contamination from the A1g channel.

关键词： Charge density waves Nematic order Kagome lattice Resistivity measurements

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Search for orbital magnetism in the kagome superconductor CsV3Sb5 using neutron diffraction

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Physical Review B 2024年第19期110卷 195109页

作者： William Liège Yaofeng Xie Dalila Bounoua Yvan Sidis Frédéric Bourdarot Yongkai Li Zhiwei Wang Jia-Xin Yin Pengcheng Dai Philippe Bourges CNRS Department of Physics and Astronomy Centre for Quantum Physics Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement (MOE) School of Physics Beijing Key Lab of Nanophotonics and Ultrafine Optoelectronic Systems Beijing Key Lab of Nanophotonics and Ultrafine Optoelectronic Systems Zhuhai 519000 China Department of Physics

As many kagome metals, the topological superconductor AV3Sb5 with (A = K,Rb,Cs) hosts a charge density wave. A related chiral flux phase that breaks the time-reversal symmetry has been further theoretically predicted in these materials. The flux phase is associated with loop currents that produce ordered orbital magnetic moments, which would occur at the momentum points, M, characterizing the charge-density wave state. Polarized neutron-diffraction experiments have been performed on an assembly of single crystals of CsV3Sb5 to search for such orbital magnetic moments. No evidence for the existence of a three-dimensionally ordered moment is found at any temperature at the first M1=(1/2,0,0) point in the Brillouin zone within an excellent experimental uncertainty, i.e., m=0±0.01μB per vanadium atom. However, the data might be suggestive of a putative magnetic orbital moment in the second Brillouin zone at M2=(1/2,1/2,0) at the detection limit of the experiment. Some loop currents patterns flowing only on vanadium triangles are able to account for this finding suggesting an ordered orbital magnetic moment of, at most, ∼0.02±0.01μB per vanadium triangle.

关键词： Charge density waves Magnetic order Kagome metal Neutron diffraction

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Three-dimensional flat band evolution between pyrochlore and perovskite lattices with enhanced anomalous Hall effect

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Physical Review B 2024年第16期109卷 165147-165147页

作者： Minjun Wang Wei Jiang Yugui Yao Centre for Quantum Physics Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement (MOE) and Beijing Key Laboratory of Nanophotonics and Ultrafine Optoelectronic Systems School of Physics Beijing Institute of Technology Beijing 100081 China

Distinct from the flat band in two dimensions, the three-dimensional (3D) flat band and the corresponding physics have been relatively unexplored. Here, based on tight-binding models, we present a theoretical study of the evolution of the 3D flat band between pyrochlore and perovskite lattices, which are structurally interconvertible through diagonal strain and host double-degenerate flat bands. We discovered the presence of a persistent 3D flat band during the transition, which is stabilized by a robust compact localized state within the preserved kagome plane perpendicular to the diagonal direction. Furthermore, under the influence of spin-orbit coupling and Zeeman field, we can consistently achieve a magnetic Weyl semimetal state during this transition process due to the unique 3D flat band nature. Pairs of Weyl points form near the conserved flat band, leading to a large anomalous Hall conductivity (AHC) peak right at the energy of the flat band. Interestingly, we also observe an enhanced AHC during the transition from pyrochlore to perovskite lattice due to the enlarged momentum separation between Weyl points and the superimposition with another AHC peak from the dispersive Dirac bands.

关键词： Anomalous Hall effect Flat bands Topological phases of matter Perovskites Pyrochlores Topological materials Tight-binding model

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Nondemolition quasiprobabilities of work and heat in the presence of a non-Markovian environment

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Physical Review A 2024年第3期109卷 032228-032228页

作者： Haiping Li Jian Zou Bin Shao Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement Ministry of Education School of Physics Beijing Institute of Technology Beijing 100081 China

We consider a collision model representation of nonequilibrium dynamics for an externally driven open quantum system. Specifically we investigate the nondemolition quasiprobability distributions (QPDFs) of work and heat in both Markovian and non-Markovian regimes. In this model, work and heat correspond to different evolution processes, and their contributions can be distinguished. For the system state with initial coherence, in both Markovian and non-Markovian regimes, negative quasiprobabilities at half of the energy gap of the system for work and the variation of internal energy appear, which is considered to be a witness of the quantumness of the system. We also find that when the external driving speed slows down, the quantumness of the system is weakened, and when the driving speed is slow enough, the negative quasiprobability will disappear and the results of the QPDF coincide with those of the two-measurement protocol. Most importantly, we find that non-Markovianity can enhance the quantumness of the system.

关键词： quantum coherence & coherence measures quantum thermodynamics quantum-to-classical transition Non-Markovian processes

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Layer-Valley Hall Effect under Inversion and Time-Reversal Symmetries

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Chinese Physics Letters 2024年第6期41卷 88-97页

作者：赵交交刘贵斌陈鹏姚裕贵张广宇杜罗军 Beijing National Laboratory for Condensed Matter Physics and Key Laboratory for Nanoscale Physics and DevicesInstitute of PhysicsChinese Academy of SciencesBeijing 100190China School of Physical Sciences University of Chinese Academy of SciencesBeijing 100190China Centre for Quantum Physics Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement(MOE)School of PhysicsBeijing Institute of TechnologyBeijing 100081China Beijing Key Lab of Nanophotonics&Ultrafine Optoelectronic Systems School of PhysicsBeijing Institute of TechnologyBeijing 100081China Schoolof Microelectronics Southern University of Science and TechnologyShenzhen 518055China Songshan Lake Materials Laboratory Dongguan 523808China

Hall effects have been the central paradigms in modern physics,materials science and practical applications,and have led to many exciting breakthroughs,including the discovery of topological Chern invariants and the revolution of metrological resistance *** date,the Hall effects have mainly focused on a single degree of freedom(Do F),and most of them require the breaking of spatial-inversion and/or time-reversal *** we demonstrate a new type of Hall effect,i.e.,layer-valley Hall effect,based on a combined layer-valley Do F characterized by the product of layer and valley *** layer-valley Hall effect has a quantum origin arising from the layer-valley contrasting Berry curvature,and can occur in nonmagnetic centrosymmetric crystals with both spatial-inversion and time-reversal symmetries,transcending the symmetry constraints of single Do F Hall effect based on the constituent layer or valley ***,the layer-valley Hall effect is highly tunable and shows a W-shaped pattern in response to the out-of-plane electric ***,we discuss the potential detection approaches and material-specific design principles of layer-valley Hall *** results demonstrate novel Hall physics and open up exotic paradigms for new research direction of layer-valleytronics that exploits the quantum nature of the coupled layer-valley DoF.

关键词： quantum Inversion curvature

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Topological materials for full-vector elastic waves

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National Science Review 2023年第5期10卷 194-200页

作者： Ying Wu Jiuyang Lu Xueqin Huang Yating Yang Li Luo Linyun Yang Feng Li Weiyin Deng Zhengyou Liu School of Physics and Optoelectronics and State Key Laboratory of Luminescent Materials and Devices South China University of Technology Institute of Solid Mechanics Midea Corporate Research CenterMidea Group Department of Astronautic Science and Mechanics Harbin Institute of Technology Centre for Quantum Physics Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement (MOE)School of PhysicsBeijing Institute of Technology Key Laboratory of Artificial Micro-and Nanostructures of Ministry of Education and School of Physics and Technology Wuhan University Institute for Advanced Studies Wuhan University

Elastic wave manipulation is important in a wide variety of applications,including information processing in small elastic devices and noise control in large solid *** recent emergence of topological materials has opened new avenues for modulating elastic waves in ***,because of the full-vector feature and the complicated couplings of the longitudinal and transverse components of elastic waves,manipulating elastic waves is generally difficult compared with manipulating acoustic waves(scalar waves) and electromagnetic waves(vectorial waves but transverse only).To date,topological materials,including insulators and semimetals,have been used for acoustic and electromagnetic *** topological materials with elastic waves have also been reported,the observed topological edge modes lie on the domain wall.A natural question arises:Is there an elastic metamaterial with topological edge modes on its own boundary?Here,we report a 3D metal-printed bilayer metamaterial that topologically insulates elastic *** introducing chiral interlayer couplings,the spin-orbit couplings for elastic waves are induced,which give rise to nontrivial topological *** edge states with vortex features were demonstrated on the boundary of the single topological *** further show a heterostructure of the metamaterial that exhibits tunable edge *** findings could be used in devices based on elastic waves in solids.

关键词： topological insulators elastic waves edge states

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Single-Molecule Confinement Induced Intrinsic Multi-Electron Redox-Activity to Enhance Supercapacitor Performance

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Energy & Environmental Materials 2023年第4期6卷 227-238页

作者： Su Yang Meiling Wang Yong Zhang Pinyi He Wenhua Cong Chongji Wang Qiankun Yang Xuguang Liu Tian Wang Xianming Zhang Jiadong Zhou College of Materials Science and Engineering Taiyuan University of TechnologyTaiyuan 030024China Key Lab of Advanced Optoelectronic Quantum Architecture and Measurement(Ministry of Education) Beijing Key Lab of Nanophotonics&Ultrafine Optoelectronic Systemsand School of PhysicsBeijing Institute of TechnologyBeijing 100081China School of Materials Science and engineering Central South UniversityChangsha 410083China Department of Chemistry National University of Singapore3 Science Drive 3117543Singapore Key Laboratory of Interface Science and Engineering in Advanced Materials Ministry of Education (Taiyuan University of Technology)Taiyuan 030024China

Aggregation of polyoxometalates(POM)is largely responsible for the reduced performance of POM-based energy-storage *** address this challenge,here,the precise confinement of single Keggin-type POM molecule in a porous carbon(PC)of unimodal super-micropore(micro-PC)is *** precise single-molecule confinement enables sufficient activity center exposure and maximum electron-transfer from micro-PC to POM,which well stabilizes the electron-accepting molecules and thoroughly activates its inherent multi-electron *** particular,the redox-activities and electron-accepting properties of the confined POM molecule are revealed to be super-micropore pore size-dependent by experiment and spectroscopy as well as theoretical ***,the molecularly dispersed POM molecules confined steadily in the“cage”of micro-PC exhibit unprecedented large-negative-potential stability and multiple-peak redox-activity at an ultra-low loading of~11.4 wt%.As a result,the fabricated solid-state supercapacitor achieves a remarkable areal capacitance,ultrahigh energy and power density of 443 mF cm^(-2),0.12 mWh cm^(-2)and 21.1 mW cm^(-2),*** work establishes a novel strategy for the precise confinement of single POM molecule,providing a versatile approach to inducing the intrinsic activity of POMs for advanced energy-storage systems.

关键词： intrinsic redox-activity polyoxometalates single-molecule confinement supercapacitor

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