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Second-order topological insulator state in hexagonal lattices and its abundant material candidates

Physical Review B 2021年第24期104卷 245427-245427页

作者： Shifeng Qian Cheng-Cheng Liu Yugui Yao Centre for Quantum Physics Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement (MOE) and Beijing Key Lab of Nanophotonics and Ultrafine Optoelectronic Systems School of Physics Beijing Institute of Technology Beijing 100081 China

We propose two mechanisms to realize the second-order topological insulator (SOTI) state in spinless hexagonal lattices, viz., chemical modification and anti-Kekulé/Kekulé distortion of hexagonal lattices. Correspondingly, we construct two models and demonstrate the nontrivial band topology of the SOTI state characterized by the second Stiefel-Whitney class w2 in the presence of inversion symmetry (P) and time-reversal symmetry (T). Based on the two mechanisms and using first-principles calculations and symmetry analysis, we predict three categories of real light element material candidates, i.e., hydrogenated and halogenated two-dimensional (2D) hexagonal group-IV materials XY (X=C, Si, Ge, Sn, Y=H, F, Cl), 2D hexagonal group-V materials (blue phosphorene, blue arsenene, and black phosphorene, black arsenene), and the recent experimentally synthesized anti-Kekulé/Kekulé order graphenes and the counterparts of silicene/germanene/stanene. We explicitly demonstrate the nontrivial topological invariants and the existence of the protected corner states with a fractional charge for these candidates with a giant bulk band gap (up to 3.5 eV), which could facilitate the experimental verification by scanning tunneling microscopy. Our approaches and proposed abundant real material candidates will greatly enrich 2D SOTIs and promote their intriguing physics research.

关键词： Electronic structure Symmetry protected topological states Topological materials

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Band tilt induced nonlinear Nernst effect in topological insulators: An efficient generation of high-performance spin polarization

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Physical Review B 2022年第8期106卷 L081121-L081121页

作者： Chuanchang Zeng Xiao-Qin Yu Zhi-Ming Yu Yugui Yao Centre for Quantum Physics Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement (MOE) School of Physics Beijing Institute of Technology Beijing 100081 China Beijing Key Lab of Nanophotonics & Ultrafine Optoelectronic Systems School of Physics Beijing Institute of Technology Beijing 100081 China School of Physics and Electronics Hunan University Changsha 410082 China

Topological insulators (TIs) hold promise as a platform for spintronics applications due to the fascinating spin-momentum locking (SML) of the surface states. One particular interest lies in using TIs as spin-polarized sources for spintronics structures. Here, we propose the band tilt induced nonlinear Nernst effect (NLNE) in TIs as a clean and efficient route to generate high-performance spin polarization (SP). We show that in the presence of SML and hexagonal warping effect a finite band tilt can induce an imbalance of two spin carriers and effectively give rise to spin-polarized NLNE current in TIs. In our scheme, both the spin current and charge current regime can be achieved under the thermal drive. The obtainable SP can be efficiently tuned in either a smooth or rapid way, exhibiting highly flexible tunability. In addition, near-unity SP can be generated within a wide range of tunable parameters, which is also found to be robust against temperature. Therefore, our work provides a mechanism to realize controllable room-temperature high-degree SP based on TIs, which is of essential importance for future spintronics applications.

关键词： Nernst effect Spin polarization Spintronics Topological insulators Transport phenomena Boltzmann theory

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Unconventional surface responses of fourfold-degenerate Dirac-nodal-line semimetals in sonic crystals

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Physical Review Applied 2023年第6期20卷 064047-064047页

作者： Chang-Yin Ji Jijie Tang Xiao-Ping Li Zheng Tang Di Zhou Yeliang Wang Feng Li Jiafang Li Yugui Yao Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement (MOE) Beijing Key Laboratory of Nanophotonics and Ultrafine Optoelectronic Systems and School of Physics Beijing Institute of Technology Beijing 100081 China School of Integrated Circuits and Electronics Ministry of Industry and Information Technology (MIIT) Key Laboratory for Low-Dimensional Quantum Structure and Devices Beijing Institute of Technology Beijing 100081 China School of Physical Science and Technology Inner Mongolia University Hohhot 010021 China

Three-dimensional nodal-line semimetals (NLSMs) are of remarkable importance for both enriching topological physics and wave management. However, NLSMs realized in acoustic systems are twofold band degenerate and are called Weyl NLSMs. Here, we report on the experimental observation of Dirac NLSMs with fourfold degeneracy in sonic crystals. We reveal that the topological properties of the Dirac NLSMs are entirely different than those of the conventional Weyl NLSMs. The Berry phase related to the Dirac nodal line (DNL) is 2π, which results in surface responses of the Dirac NLSMs in two radically different situations: a torus surface state occupying the entire surface Brillouin zone (SBZ) and one without any surface state in the SBZ. We further reveal that topological surface arcs caused by the DNL can change from open to closed contours. The findings of Dirac NLSMs and their unique surface response may bring about exciting frontiers for the flexible manipulation of acoustic surface waves.

关键词： Acoustic metamaterials Edge states Geometric & topological phases Topological insulators Dirac semimetal Semimetals Weyl semimetal

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Crystal symmetry selected pure spin photocurrent in altermagnetic insulators

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Physical Review B 2025年第19期111卷 195210-195210页

作者： Ruizhi Dong Ranquan Cao Dian Tan Ruixiang Fei School of Physics Beijing Institute of Technology Beijing 100081 China Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement (Ministry of Education) Beijing Institute of Technology Beijing 100081 China Shenzhen Institute for Quantum Science and Engineering and Department of Physics Southern University of Science and Technology Shenzhen 518055 China

The generation of time-reversal-odd spin current in metallic altermagnets has attracted considerable interest in spintronics. However, producing pure spin current in insulating materials remains both challenging and desirable, as insulating states are frequently found in antiferromagnets. Nonlinear photogalvanic effects offer a promising method for generating spin current in insulators. We here reveal that spin and charge photocurrents in altermagnets are protected by spin point group symmetry. The shift and injection current mechanisms simultaneously induce spin-momentum locking in a specific direction in altermagnets regardless of spin-orbit coupling (SOC), exhibiting pure spin current. This stands in contrast to parity-time symmetric antiferromagnets, where SOC induces a charge current alongside the spin current, thereby preventing the generation of a pure spin current. We applied our predictions using first-principles calculations to several distinct materials, including wurtzite MnTe and multiferroic BiFeO3. Additionally, we elucidated the linear-inject-current mechanism in BiFeO3 induced by SOC, which may account for the enhanced bulk photovoltaic effect in multiferroics.

关键词： Point groups

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Scanning tunneling microscopy study of twisted Bernal-stacked tetralayer graphene

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Physical Review B 2025年第11期111卷 115410-115410页

作者： Wen-Xiao Wang Tongtong Chen Long-Jing Yin Jiabin Qiao Zhen Ma Juntao Song Hebei Advanced Thin Films Laboratory Hebei Normal University Shijiazhuang Hebei 050024 China Postdoctoral Research Station at Hebei Normal University Shijiazhuang 050024 China School of Physics and Electronics Hunan University Changsha 410082 China Centre for Quantum Physics Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement School of Physics Beijing Institute of Technology Beijing 100081 China School of Electronics and Information Zhengzhou University of Light Industry Zhengzhou 450002 China

Twisted multilayer graphene provides an unprecedented platform for studying strongly correlated and topological physics, such as twisted monobilayer graphene (TMBG) featured with electric-field tunable superconductivity. Adding an extra layer to TMBG, twisted tetralayer graphene emerges with more fascinating correlated phases related to crystal symmetry and band structure. In this study, by using scanning tunneling microscope, we thoroughly investigated twisted Bernal-stacked tetralayer graphene with a small twist angle in three distinct configurations: a twist between monotrilayer (A/BAB), bibilayer (AB/AB), and trimonolayer (ABA/B). All three types host almost the same twist angle induced by as-grown grain boundaries. We detected two distinct scanning tunneling spectroscopy spectra on the A/BAB- and ABA/B-type tetralayer graphene, indicative of mirror-symmetry breaking. Notably, both flat and linear bands coexist in the tetralayer system with a small twist angle, which supports emerging correlated phases. Moreover, our result revealed layer-dependent distribution of local density of states assigned to the flat and linear bands in twisted tetralayer graphene. Intriguingly, the flat-band localization becomes weakened as the twisted interface recedes from the top to bottom layers. This work not only sheds light on structural and electronic properties of twisted tetralayer graphene in distinct configurations, but also opens up further opportunities in understanding correlated physics in twisted multilayer graphene system.

关键词： Crystal symmetry

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Hilbert band complexes and their applications

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Physical Review B 2025年第7期111卷 075154-075154页

作者： Zeying Zhang Y. X. Zhao Yugui Yao Shengyuan A. Yang College of Mathematics and Physics Beijing University of Chemical Technology Beijing 100029 China Department of Physics and HKU-UCAS Joint Institute for Theoretical and Computational Physics at Hong Kong The University of Hong Kong Pokfulam Road Hong Kong China Centre for Quantum Physics Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement (MOE) Beijing Institute of Technology Beijing 100081 China Research Laboratory for Quantum Materials IAPME FST University of Macau Macau China

The study of band connectivity is a fundamental problem in condensed matter physics. Here, we develop a method for analyzing band connectivity, which completely solves the outstanding questions of the reducibility and decomposition of band complexes. By translating the symmetry conditions into a set of band balance equations, we show that all possible band structure solutions can be described by a positive affine monoid structure, which has a unique minimal set of generators, called Hilbert basis. We show that Hilbert basis completely determines whether a band complex is reducible and how it can be decomposed. The band complexes corresponding to Hilbert basis vectors, termed as Hilbert band complexes (HBCs), can be regarded as elementary building blocks of band structures. We develop algorithms to construct HBCs, analyze their graph features, and merge them into large complexes. We find some interesting examples, such as HBCs corresponding to complete bipartite graphs, and complexes that can grow without bound by successively merging a HBC.

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Secondary complementary balancing compressive imaging with a free-space balanced amplified photodetector

arXiv

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arXiv 2022年

作者： Yu, Wen-Kai Yang, Ying Liu, Jin-Rui Wei, Ning Wang, Shuo-Fei Center for Quantum Technology Research Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement Ministry of Education School of Physics Beijing Institute of Technology Beijing100081 China

Single-pixel imaging (SPI) has attracted widespread attention because it generally uses a non-pixelated photodetector and a digital micromirror device (DMD) to acquire the object image. Since the modulated patterns seen from two reflection directions of the DMD are naturally complementary, one can apply complementary balanced measurements to greatly improve the measurement signal-to-noise ratio and reconstruction quality. However, the balance between two reflection arms significantly determines the quality of differential measurements. In this work, we propose and demonstrate a simple secondary complementary balancing mechanism to minimize the impact of the imbalance on the imaging system. In our SPI setup, we used a silicon free-space balanced amplified photodetector with 5 mm active diameter which could directly output the difference between two optical input signals in two reflection arms. Both simulation and experimental results have demonstrated that the use of secondary complementary balancing can result in a better cancellation of direct current components of measurements and a better image restoration quality. Copyright © 2022, The Authors. All rights reserved.

关键词： Image reconstruction

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Multi-party interactive cryptographic key distribution protocol over a public network based on computational ghost imaging

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OPTICS AND LASERS IN ENGINEERING 2022年 155卷

作者： Yu, Wen-Kai Wei, Ning Li, Ya-Xin Yang, Ying Wang, Shuo-Fei [a]Center for Quantum Technology Research School of Physics Beijing Institute of Technology Beijing 100081 China [b]Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement of Ministry of Education School of Physics Beijing Institute of Technology Beijing 100081 China

In existing ghost-imaging-based cryptographic key distribution (CKD) protocols, the lack of joint identity authentication leads to potential security risks. Here, under a computational ghost imaging framework, we propose a multi-party interactive CKD protocol over a public network, which sets an intermediary to perform fragment synthesis-based joint identity authentication. The fragment images can be acquired with high quality via a binarization process. Both simulation and experiments have demonstrated that this proposed protocol can greatly improve the security of communication. Thus, this protocol paves a new way for authentication in multi-party CKD.

关键词： Cryptographic key distribution Interactive joint authentication Binarization processing Multi-party optical communication Computational ghost imaging

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Nonlinear Topological Mechanics in Elliptically Geared Isostatic Metamaterials

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Physical Review Letters 2023年第4期131卷 046101-046101页

作者： Fangyuan Ma Zheng Tang Xiaotian Shi Ying Wu Jinkyu Yang Di Zhou Yugui Yao Feng Li Key Lab of Advanced Optoelectronic Quantum Architecture and Measurement (MOE) School of Physics Beijing Institute of Technology Beijing 100081 China Aeronautics and Astronautics University of Washington Seattle Washington 98195 USA School of Science Nanjing University of Science and Technology Nanjing 210094 China Mechanical Engineering Seoul National University Seoul 08826 Korea

Despite the extensive studies of topological systems, the experimental characterizations of strongly nonlinear topological phases have been lagging. To address this shortcoming, we design and build elliptically geared isostatic metamaterials. Their nonlinear topological transitions can be realized by collective soliton motions, which stem from the transition of nonlinear Berry phase. Endowed by the intrinsic nonlinear topological mechanics, surface polar elasticity and dislocation-bound zero modes can be created or annihilated as the topological polarization reverses orientation. Our approach integrates topological physics with strongly nonlinear mechanics and promises multiphase structures at the micro- and macroscales.

关键词： Classical mechanics Elasticity Phase transitions Topological phases of matter

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Optimizing attosecond-pulse generation in solids by modulating electronic dynamics with a monochromatic laser field

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Physical Review A 2025年第2期111卷 023521-023521页

作者： Xinyuan Zhang Shiqi Hu Mengxue Guan Sheng Meng Beijing National Laboratory for Condensed Matter Physics and Institute of Physics Chinese Academy of Sciences Beijing 100190 China School of Physical Sciences University of Chinese Academy of Sciences Beijing 100190 China Centre for Quantum Physics Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement (Ministry of Education) School of Physics Beijing Institute of Technology Beijing 100081 China Songshan Lake Materials Laboratory Dongguan Guangdong 523808 China

A practical approach is proposed for efficiently generating ultrashort attosecond pulses from realistic solid-state materials, aiming to optimize pulse width effectively. By adjusting the photon energy while maintaining a constant peak electric field, this strategy modulates the peak vector potential and laser field period, thereby controlling the high harmonic cutoff energy and the time-domain emission characteristics of the harmonics. The field-driven electronic dynamics lead to a nonmonotonic variation in both the intensity and the duration of the generated attosecond pulses. The light field frequency can be adjusted to yield the optimal pulse. Beyond the primary demonstration with hexagonal boron nitride as a prototypical material, significant pulse width optimization has been achieved across a range of different materials. This straightforward and versatile strategy shows promise for application in solid-state materials, offering new pathways to promote high harmonic performance.

关键词： Boron nitride

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