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Dynamical classification of topological quantum phases

Science Bulletin 2018年第21期63卷 1385-1391页

作者： Lin Zhang Long Zhang Sen Niu xiong-jun liu International Center for Quantum Materials School of PhysicsPeking UniversityBeijing 100871China Collaborative Innovation Center of Quantum Matter Beijing 100871China Institute for Quantum Science and Engineering and Department of Physics Southern University of Science and TechnologyShenzhen 518055China

Topological phase of matter is now a mainstream of research in condensed matter physics, of which the classification, synthesis, and detection of topological states have brought excitements over the recent decade while remain incomplete with ongoing challenges in both theory and experiment. Here we propose to establish a universal non-equilibrium characterization of the equilibrium topological quantum phases classified by integers, and further propose the high-precision dynamical schemes to detect such states. The framework of the dynamical classification theory consists of basic theorems. First, we uncover that classifying a d-dimensional(dD) gapped topological phase of generic multibands can reduce to a(d-1)D invariant defined on so-called band inversion surfaces(BISs), rendering a bulk-surface duality which simplifies the topological characterization. Further, we show in quenching across phase boundary the(pseudo) spin dynamics to exhibit unique topological patterns on BISs, which are attributed to the post-quench bulk topology and manifest a dynamical bulk-surface correspondence. For this the topological phase is classified by a dynamical topological invariant measured from an emergent dynamical spintexture field on the BISs. Applications to quenching experiments on feasible models are proposed and studied, demonstrating the new experimental strategies to detect topological phases with high feasibility. This work opens a broad new direction to classify and detect topological phases by non-equilibrium quantum dynamics.

关键词： Quench dynamics Topological quantum phase Band inversion surface Bulk-surface duality Dynamical topological invariant Ultracold atoms Synthetic gauge field

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Topological holographic quench dynamics in a synthetic frequency dimension

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Light(Science & Applications) 2021年第11期10卷 2184-2194页

作者： Danying Yu Bo Peng Xianfeng Chen xiong-jun liu Luqi Yuan State Key Laboratory of Advanced Optical Communication Systems and Networks School of Physics and AstronomyShanghai Jiao Tong University200240ShanghaiChina Shanghai Research Center for Quantum Sciences 201315ShanghaiChina Jinan Institute of Quantum Technology 250101JinanChina Collaborative Innovation Center of Light Manipulations and Applications Shandong Normal University250358JinanChina International Center for Quantum Materials and School of Physics Peking University100871BeijingChina Shenzhen Institute for Quantum Science and Engineering Southern University of Science and Technology518055ShenzhenChina

The notion of topological phases extended to dynamical systems stimulates extensive studies,of which the characterization of nonequilibrium topological invariants is a central issue and usually necessitates the information of quantum dynamics in both the time and momentum ***,we propose the topological holographic quench dynamics in synthetic dimension,and also show it provides a highly efficient scheme to characterize photonic topological phases.A pseudospin model is constructed with ring resonators in a synthetic lattice formed by frequencies of light,and the quench dynamics is induced by initializing a trivial state,which evolves under a topological *** key prediction is that the complete topological information of the Hamiltonian is encoded in quench dynamics solely in the time dimension,and is further mapped to lower-dimensional space,manifesting the holographic features of the *** particular,two fundamental time scales emerge in the dynamical evolution,with one mimicking the topological band on the momentum dimension and the other characterizing the residue time evolution of the state after the *** this,a universal duality between the quench dynamics and the equilibrium topological phase of the spin model is obtained in the time dimension by extracting information from the field evolution dynamics in modulated ring systems in *** work also shows that the photonic synthetic frequency dimension provides an efficient and powerful way to explore the topological nonequilibrium dynamics.

关键词： dynamics dimension topological

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Topological superradiant state in Fermi gases with cavity induced spin-orbit coupling

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Frontiers of physics 2018年第1期13卷 129-141页

作者： Dongyang Yu Jian-Song Pan xiong-jun liu Wei Zhang Wei Yi Department of Physics Renmin University of China Beijing 100872 China Key Laboratory of Quantum Inforraation University of Science and Technology of China CAS Hefei 230026 China Synergetic innovation Center of Quantum Information and Quantum Physics University of Science and Technology of China Hefei 230026 China International Center for Quantum Materials School of Physics Peking University Beijing 100871 China Collaborative Innovation Center of Quantum Matter Beijing 100871 China Beijing Key Laboratory of Opto-electronic Functional Materials and Micro-nano Devices Renmin University of China Beijing 100872 China

Coherently driven atomic gases inside optical cavities hold great promise for generating rich dynam- ics and exotic states of matter. It was shown recently that. an exotic topological superradiant state exists in a two-component degenerate Fermi gas coupled to a cavity, where local order parameters coexist with global topological invariants. In this work, we characterize in detail various properties of this exotic state, focusing on the feedback interactions between the atoms and the cavity field. In particular, we demonstrate that cavity-induced interband coupling plays a crucial role in inducing the topological phase transition between the conventional and topological superradiant states. We analyze the interesting signatures in the cavity field left by the closing and reopening of the atomic bulk gap across the topological phase boundary and discuss the robustness of the topological superradiant state by investigating the steady-state phase diagram under various conditions. Furthermore, we consider the interaction effect and discuss the interplay between the pairing order in atomic ensembles and the superradiance of the cavity mode. Our work provides many valuable insights into the unique cavity-atom hybrid system under study and is helpful for future experimental exploration of the topological superradiant state.

关键词： superradiance topological phase Fermi gas cavity QED

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Discovery of tip induced unconventional superconductivity on Weyl semimetal

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Science Bulletin 2017年第6期62卷 425-430页

作者： He Wang Huichao Wang Yuqin Chen Jiawei Luo Zhujun Yuan jun liu Yong Wang Shuang Jia xiong-jun liu jian Wei Jian Wang International Center for Quantum Materials School of Physics Peking University Beijing 100871 China Collaborative Innovation Center of Quantum Matter Beijing China Center of Electron Microscopy State Key Laboratory of Silicon Materials School of Materials Sdence and Engineering Zhejiang University Hangzhou 310027 China

Weyl fermion is a massless Dirac fermion with definite chirality,which has been long pursued since *** it has not been observed as a fundamental particle in nature,Weyl fermion can be realized as low-energy excitation around Weyl point in Weyl semimetal,which possesses Weyl fermion cones in the bulk and nontrivial Fermi arc states on the surface. As a firstly discovered Weyl semimetal,Ta As crystal possesses 12 pairs of Weyl points in the momentum space,which are topologically protected against small perturbations. Here,we report for the first time the tip induced superconductivity on Ta As crystal by point contact spectroscopy. The zero bias conductance peak as well as a conductance plateau with double conductance peaks and sharp double dips are observed in the point contact spectra simultaneously,indicating unconventional superconductivity. Our further theoretical study suggests that the induced superconductivity may have nontrivial topology. The present work opens a new route in investigating the novel superconducting states based on Weyl materials.

关键词： Tip induced unconventional superconductivity Topological superconductivity Weyl semimetal TaAs Point contact spectroscopy

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Surface superconductivity in the type Ⅱ Weyl semimetal TaIrTe4

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National Science Review 2020年第3期7卷 579-587页

作者： Ying Xing Zhibin Shao jun Ge Jiawei Luo Jinhua Wang Zengwei Zhu jun liu Yong Wang Zhiying Zhao Jiaqiang Yan David Mandrus Binghai Yan xiong-jun liu Minghu Pan Jian Wang Department of Materials Science and Engineering College of New Energy and Materials China University of Petroleum International Center for Quantum Materials School of Physics Peking University School of Physics and Information Technology Shaanxi Normal University School of Physics Huazhong University of Science and Technology Wuhan National High Magnetic Field Center Huazhong University of Science and Technology Center of Electron Microscopy State Key Laboratory of Silicon Materials School of Materials Science and Engineering Zhejiang University Department of Materials Science and Engineering University of Tennessee Department of Physics and Astronomy University of Tennessee Materials Science and Technology Division Oak Ridge National Laboratory Department of Condensed Matter Physics Weizmann Institute of Science CAS Center for Excellence in Topological Quantum Computation University of Chinese Academy of Sciences Beijing Academy of Quantum Information Sciences Collaborative Innovation Center of Quantum Matter

The search for unconventional superconductivity in Weyl semimetal materials is currently an exciting pursuit, since such superconducting phases could potentially be topologically non-trivial and host exotic Majorana modes. The layered material TaIrTe4is a newly predicted time-reversal invariant type Ⅱ Weyl semimetal with the minimum number of Weyl points. Here, we report the discovery of surface superconductivity in Weyl semimetal Ta Ir Te4. Our scanning tunneling microscopy/spectroscopy(STM/STS) visualizes Fermi arc surface states of TaIrTe4that are consistent with the previous angle-resolved photoemission spectroscopy results. By a systematic study based on STS at ultralow temperature, we observe uniform superconducting gaps on the sample surface. The superconductivity is further confirmed by electrical transport measurements at ultralow temperature, with an onset transition temperature(Tc) up to 1.54 K being observed. The normalized upper critical field h*(T/Tc) behavior and the stability of the superconductivity against the ferromagnet indicate that the discovered superconductivity is unconventional with the p-wave pairing. The systematic STS, and thickness-and angular-dependent transport measurements reveal that the detected superconductivity is quasi-1 D and occurs in the surface states. The discovery of the surface superconductivity in TaIrTe4provides a new novel platform to explore topological superconductivity and Majorana modes.

关键词： surface superconductivity Weyl semimetal topological superconductivity

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Direct extraction of topological Zak phase with the synthetic dimension

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Light(Science & Applications) 2023年第4期12卷 671-679页

作者： Guangzhen Li Luojia Wang Rui Ye Yuanlin Zheng Da-Wei Wang xiong-jun liu Avik Dutt Luqi Yuan Xianfeng Chen State Key Laboratory of Advanced Optical Communication Systems and Networks School of Physics and AstronomyShanghai Jiao Tong UniversityShanghai 200240China Shanghai Research Center for Quantum Sciences Shanghai 201315China Interdisciplinary Center for Quantum Information and Zhejiang Province Key Laboratory of Quantum Technology and Device Department of PhysicsZhejiang UniversityHangzhou 310027China InternationalCenter for Quantum Materials and School of Physics Peking UniversityBeijing 100871China International Quantum Academy Shenzhen 518048China Department of Mechanical Engineering Institute for Physical Science and TechnologyUniversity of MarylandCollege ParkMD 20742USA Collaborative Innovation Center of Light Manipulation and Applications Shandong Normal UniversityJinan 250358China

Measuring topological invariants is an essential task in characterizing topological phases of *** are usually obtained from the number of edge states due to the bulk-edge correspondence or from interference since they are integrals of the geometric phases in the energy *** is commonly believed that the bulk band structures could not be directly used to obtain the topological ***,we implement the experimental extraction of Zak phase from the bulk band structures of a Su-Schrieffer-Heeger(SSH)model in the synthetic frequency *** synthetic SSH lattices are constructed in the frequency axis of light,by controlling the coupling strengths between the symmetric and antisymmetric supermodes of two bichromatically driven *** measure the transmission spectra and obtain the projection of the time-resolved band structure on lattice sites,where a strong contrast between the non-trivial and trivial topological phases is *** topological Zak phase is naturally encoded in the bulk band structures of the synthetic SSH lattices,which can hence be experimentally extracted from the transmission spectra in a fiber-based modulated ring platform using a laser with telecom *** method of extracting topological phases from the bulk band structure can be further extended to characterize topological invariants in higher dimensions,while the exhibited trivial and non-trivial transmission spectra from the topological transition may find future applications in optical communications.

关键词： topological trivial synthetic

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Phase field modeling of grain stability of nanocrystalline alloys by explicitly incorporating mismatch strain

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Rare Metals 2024年第7期43卷 3370-3382页

作者： Min Zhou Hong-Hui Wu Yuan Wu Hui Wang xiong-jun liu Sui-He Jiang Xiao-Bin Zhang Zhao-Ping Lu Beijing Advanced Innovation Center for Materials Genome Engineering State Key Laboratory for Advanced Metals and MaterialsUniversity of Science and Technology BeijingBeijing 100083Cnina Institute for Carbon Neutrality University of Science and TechnologyBeijing 100083China Institute of Materials Intelligent Technology Liaoning Academy of MaterialsShenyang 110004China

Ab st ra ct Nanocrystalline materials exhibit unique properties due to their extremely high grain boundary(GB) ***,this high-density characteristic induces grain coarsening at elevated temperatures,thereby limiting the widespread application of nanocrystalline *** experimental observations revealed that GB segregation and second-phase pinning effectively hinder GB migration,thereby improving the stability of nanocry stalline *** this study,a mouified phase-field model that integrates mismatch strain,solute segregation and precipitation was developed to evaluate the influence of lattice misfit on the thermal stability of nanocrystalline *** simulation results indicated that introducing a suitable mismatch strain can effectively enhance the microstructural stability of nanocrystalline *** synergizing precipitation with an appropriate lattice misfit,the formation of second-phase particles in the bulk grains can be suppressed,thereby facilitating solute segregation/precipitation at the *** concentrated solute segregation and precipitation at the GBs effectively hinders grain migration,thereby preventing grain *** findings provide a new perspective on the design and regulation of nanocrystalline alloys with enhanced thermal stability.

关键词： Phase field model Mismatch strain Second-phase precipitation Grain boundary segregation Nanocrystalline alloys

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Precision mapping the topological bands of 2D spin-orbit coupling with microwave spin-injection spectroscopy

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Science Bulletin 2018年第22期63卷 1464-1469页

作者： Xiao-Tian Xu Chang-Rui Yi Bao-Zong Wang Wei Sun Youjin Deng xiong-jun liu Shuai Chen Jian-Wei Pan Shanghai Branch National Research Center for Physical Sciences at Microscale and Department of Modern PhysicsUniversity of Science and Technology of ChinaShanghai 201315China Chinese Academy of Sciences Center for Excellence:Quantum Information and Quantum Physics University of Science and Technology of ChinaHefei 230326China International Center for Quantum Materials School of PhysicsPeking UniversityBeijing 100871China Collaborative Innovation Center of Quantum Matter Beijing 100871China

To investigate the band structure is one of the key approaches to study the fundamental properties of a novel *** report here the precision band mapping of a 2-dimensional(2D) spin-orbit(SO) coupling in an optical *** applying the microwave spin-injection spectroscopy, the band structure and spin-polarization distribution are achieved *** band topology is also addressed with observing the band gap close and re-open at the Dirac ***, the lattice depth and the Raman coupling strength are precisely calibrated with relative errors in the order of 10^(-3).Our approach could also be applied for exploring the exotic topological phases with even higher dimensional system.

关键词： 2D spin-orbit coupling Microwave spin-injection spectroscopy Spin polarization Topological band Topological phase transition

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Universal topological quench dynamics for Z_(2)topological phases

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Science Bulletin 2022年第12期67卷 1236-1242,M0004页

作者： Lin Zhang Wei Jia xiong-jun liu International Center for Quantum Materials and School of Physics Peking UniversityBeijing 100871China Collaborative Innovation Center of Quantum Matter Beijing 100871China CAS Center for Excellence in Topological Quantum Computation University of Chinese Academy of SciencesBeijing 100190China Institute for Quantum Science and Engineering and Department of Physics Southern University of Science and TechnologyShenzhen 518055China

The free-fermion topological phases with Z_(2)invariants cover a broad range of topological states,including the time-reversal invariant topological insulators,and are defined on the equilibrium ground *** such equilibrium topological phases have universal correspondence to far-from-equilibrium quantum dynamics is a fundamental issue of both theoretical and experimental *** we uncover the universal topological quench dynamics linking to these equilibrium topological phases of different dimensionality and symmetry classes in the tenfold way,with a general framework being *** show a novel result that a generic d-dimensional topological phase represented by Dirac type Hamiltonian and with Z_(2)invariant defined on high symmetry momenta can be characterized by topology reduced to certain arbitrary discrete momenta of Brillouin zone called the highest-order bandinversion *** dimension-reduced topology has unique correspondence to the topological pattern emerging in far-from-equilibrium quantum dynamics by quenching the system from trivial phase to the topological regime,rendering the dynamical hallmark of the equilibrium topological *** work completes the dynamical characterization for the full tenfold classes of topological phases,which can be partially extended to even broader topological phases protected by lattice symmetries and in non-Dirac type systems,and shall advance widely the research in theory and experiment.

关键词： Z_(2)topological quantum phase Band-inversion surface Quench dynamics Topological characterization Quantum simulation

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Ideal Weyl semimetal with 3D spin-orbit coupled ultracold quantum gas

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Science Bulletin 2020年第24期65卷 2080-2085,M0005页

作者： Yue-Hui Lu Bao-Zong Wang xiong-jun liu International Center for Quantum Materials and School of Physics Peking UniversityBeijing 100871China Collaborative Innovation Center of Quantum Matter Beijing 100871China Shanghai Branch National Laboratory for Physical Sciences at Microscale and Department of Modem PhysicsUniversity of Science and Technology of ChinaShanghai 201315China CAS Center for Excellence in Topological Quantum Computation University of Chinese Academy of SciencesBeijing 100190China

There is an immense effort in search for various types of Weyl semimetals, of which the most fundamental phase consists of the minimal number of i.e. two Weyl points, but is hard to engineer in solids. Here we demonstrate how such fundamental Weyl semimetal can be realized in a maneuverable optical Raman lattice, with which the three-dimensional(3D) spin-orbit(SO) coupling is synthesised for ultracold atoms. In addition, a new novel Weyl phase with coexisting Weyl nodal points and nodal ring is also predicted here, and is shown to be protected by nontrivial linking numbers. We further propose feasible techniques to precisely resolve 3D Weyl band topology through 2D equilibrium and dynamical measurements. This work leads to the first realization of the most fundamental Weyl semimetal band and the 3D SO coupling for ultracold quantum gases, which are respectively the significant issues in the condensed matter and ultracold atom physics.

关键词： Weyl semimetal Spin-orbit coupling Topological quantum phase Ultracold atoms Optical lattice Quench dynamics

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