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Enhanced Anomalous Hall Effect in Magnetic Topological Semimetal Co3Sn{2-x}InxS2

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arXiv 2020年

作者： Zhou, Huibin Chang, Guoqing Wang, Guangqiang Gui, Xin Xu, Xitong Yin, Jia-Xin Guguchia, Zurab Zhang, Songtian S. Chang, Tay-Rong Lin, Hsin Xie, Weiwei Hasan, M. Zahid Jia, Shuang International Center for Quantum Materials School of Physics Peking University China Department of Physics Princeton University PrincetonNJ08544 United States Department of Chemistry Louisiana State University Baton RougeLA70803 United States Laboratory for Muon Spin Spectroscopy Paul Scherrer Institute Villigen PSICH-5232 Switzerland Department of Physics National Cheng Kung University Tainan701 Taiwan Institute of Physics Academia Sinica Taipei11529 Taiwan Princeton Institute for Science and Technology of Materials Princeton University PrincetonNJ08544 United States Materials Science Division Lawrence Berkeley National Laboratory BerkeleyCA94720 United States Collaborative Innovation Center of Quantum Matter Beijing100871 China CAS Center for Excellence in Topological Quantum Computation University of Chinese Academy of Sciences Beijing100190 China Beijing Academy of Quantum Information Sciences West Building 3 No. 10 Xibeiwang East Road Haidian District Beijing100193 China

We study the anomalous Hall Effect (AHE) of single-crystalline Co3Sn2−xInxS2 over a large range of indium concentration x from 0 to 1. Their magnetization reduces progressively with increasing x while their ground state evolves from a ferromagnetic Weyl semimetal into a nonmagnetic insulator. Remarkably, after systematically scaling the AHE, we find that their intrinsic anomalous Hall conductivity (AHC) features an unexpected maximum at around x = 0.15. The change of the intrinsic AHC corresponds with the doping evolution of Berry curvature and the maximum arises from the magnetic topological nodal-ring gap. Our experimental results show a larger AHC in a fundamental nodal-ring gap than that of Weyl nodes. Copyright © 2020, The Authors. All rights reserved.

关键词： Topology

Interlayer correlated fractional quantum Hall state in the ν = 4/5 bilayer system

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arXiv 2019年

作者： Wang, Hao Seidel, Alexander Yang, Kun Zhang, Fu-Chun Shenzhen Institute for Quantum Science and Engineering Department of Physics Southern University of Science and Technology Shenzhen518055 China Department of Physics Washington University St. LouisMO63130 United States Physics Department National High Magnetic Field Laboratory Florida State University TallahasseeFL32310 United States Kavli Institute for Theoretical Sciences CAS Center for Topological Quantum Computation University of Chinese Academy of Sciences Beijing100190 China

We perform exact diagonalization studies for fractional quantum Hall states at filing factor 4/5 in a bilayer system, on a torus with various aspect ratios and angles. We find that in the absence of tunneling, two weakly coupled 2/5-layers undergo a phase transition into an interlayer-correlated regime, which is also Abelian with the five-fold degeneracy on the torus. In the limit of zero layer separation, this phase becomes a singlet in the pseudospin variable describing the layer degree-of-freedom. By studying the Chern-number matrix, we show that the K-matrix describing the interlayer-correlated regime requires matrix dimension larger than two and this regime is in particular not described by a Halperin state. A detailed analysis of possible 4 × 4 K-matrices having the requisite symmetries and quantum numbers shows that there is only one equivalence class of such matrices. A model wave function representing this universality class is constructed. The role of separate particle number conservation in both layers is discussed, and it is argued that this additional symmetry allows for the further distinction of two different symmetry protected Abelian phases in the interlayer correlated regime. Interlayer tunneling breaks this symmetry, and can drive the system into a single-layer regime when strong enough. A qualitative phase diagram in the tunneling-layer separation parameter space is proposed based on our numerical results. Copyright © 2019, The Authors. All rights reserved.

关键词： Matrix algebra

Frontispiece: Perylene Diimide-Based Conjugated Polymers for All-Polymer Solar Cells

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Chemistry – A European Journal 2020年第55期26卷

作者： Prof. Qinqin Shi Jianfei Wu Xiaoxi Wu Prof. Aidong Peng Prof. Hui Huang College of Materials Science and Opto-Electronic Technology & Center of Materials Science and Optoelectronics Engineering & CAS Center for Excellence in Topological Quantum Computation & CAS Key Laboratory of Vacuum Physics University of Chinese Academy of Sciences Beijing 100049 P. R. China

Optical spectroscopy study of the topological property in PrSb

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Physical Review B 2019年第11期100卷 115133-115133页

作者： W. J. Ban D. S. Wu C. C. Le J. P. Hu J. L. Luo H. Xiao Center for High Pressure Science and Technology Advanced Research Beijing 100094 China Beijing National Laboratory for Condensed Matter Physics Institute of Physics Chinese Academy of Sciences P.O. Box 603 Beijing 100190 China School of Physical Sciences University of Chinese Academy of Sciences Beijing 100049 China Kavli Institute for Theoretical Sciences and CAS Center for Excellence in Topological Quantum Computation University of Chinese Academy of Sciences Beijing 100190 China Beijing National Research Center for Condensed Matter Physics and Institute of Physics Chinese Academy of Sciences Beijing 100190 China South Bay Interdisciplinary Science Center Dongguan Guangdong Province 523808 China

We report an optical spectroscopy study of a single-crystal sample of PrSb, one of the monoantimonide RSb compounds, which show interesting properties, such as topological nontrivial surface states and extremely large magnetoresistance. The plasma frequency is revealed at about 4300cm−1, suggesting a low carrier density. In addition, we found two quasilinear components with variable slopes in the real part of the optical conductivity σ1(ω). In combination with theoretical calculations which reveal a band inversion, our results may provide optical spectroscopic evidence of a topological nontrivial property in PrSb.

关键词： Electronic structure Optical conductivity Phonons Spin-orbit coupling Topological materials

Observation of half-integer level shift of vortex bound states in an iron-based superconductor

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arXiv 2019年

作者： Kong, Lingyuan Zhu, Shiyu Papaj, Michal Cao, Lu Isobe, Hiroki Liu, Wenyao Wang, Dongfei Fan, Peng Chen, Hui Sun, Yujie Du, Shixuan Schneeloch, John Zhong, Ruidan Gu, Genda Fu, Liang Gao, Hong-Jun Ding, Hong Beijing National Laboratory for Condensed Matter Physics Institute of Physics Chinese Academy of Sciences Beijing100190 China School of Physical Sciences University of Chinese Academy of Sciences Beijing100190 China Department of Physics Massachusetts Institute of Technology CambridgeMA02139 United States CAS Center for Excellence in Topological Quantum Computation University of Chinese Academy of Sciences Beijing100190 China Condensed Matter Physics and Materials Science Department Brookhaven National Laboratory UptonNY11973 United States Songshan Lake Materials Laboratory Dongguan Guangdong523808 China

Vortices in topological superconductors host Majorana zero modes (MZMs), which are proposed to be building blocks of fault-tolerant topological quantum computers. Recently, a new single-material platform for realizing MZM has been discovered in iron-based superconductors, without involving hybrid semiconductor-superconductor structures. Here we report on a detailed scanning tunneling spectroscopy study of a FeTe0.55Se0.45 single crystal, revealing two distinct classes of vortices present in this system which differ by a half-integer level shift in the energy spectra of the vortex bound states. This level shift is directly tied with the presence or absence of zero-bias peak and also alters the ratios of higher energy levels from integer to half-odd-integer. Our model calculations fully reproduce the spectra of these two types of vortex bound states, suggesting the presence of topological and conventional superconducting regions that coexist within the same crystal. Our findings provide strong evidence for the topological nature of superconductivity in FeTe0.55Se0.45 and establish it as an excellent platform for further studies on MZMs. Copyright © 2019, The Authors. All rights reserved.

关键词： Iron-based Superconductors

Nearly quantized conductance plateau of vortex zero mode in an iron-based superconductor

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arXiv 2019年

作者： Zhu, Shiyu Kong, Lingyuan Cao, Lu Chen, Hui Papaj, Michal Du, Shixuan Xing, Yuqing Liu, Wenyao Wang, Dongfei Shen, Chengmin Yang, Fazhi Schneeloch, John Zhong, Ruidan Gu, Genda Fu, Liang Zhang, Yu-Yang Ding, Hong Gao, Hong-Jun Beijing National Laboratory for Condensed Matter Physics Institute of Physics Chinese Academy of Sciences Beijing100190 China School of Physical Sciences University of Chinese Academy of Sciences Beijing100190 China CAS Center for Excellence in Topological Quantum Computation University of Chinese Academy of Sciences Beijing100190 China Condensed Matter Physics and Materials Science Department Brookhaven National Laboratory UptonNY11973 United States Department of Physics Massachusetts Institute of Technology CambridgeMA02139 United States Songshan Lake Materials Laboratory Dongguan Guangdong523808 China

Majorana zero-modes (MZMs) are spatially-localized zero-energy fractional quasiparticles with non-Abelian braiding statistics that hold a great promise for topological quantum computing. Due to its particle-antiparticle equivalence, an MZM exhibits robust resonant Andreev reflection and 2e2/h quantized conductance at low temperature. By utilizing variable-tunnel-coupled scanning tunneling spectroscopy, we study tunneling conductance of vortex bound states on FeTe0.55Se0.45 superconductors. We report observations of conductance plateaus as a function of tunnel coupling for zero-energy vortex bound states with values close to or even reaching the 2e2/h quantum conductance. In contrast, no such plateau behaviors were observed on either finite energy Caroli-de Genne-Matricon bound states or in the continuum of electronic states outside the superconducting gap. This unique behavior of the zero-mode conductance reaching a plateau strongly supports the existence of MZMs in this iron-based superconductor, which serves as a promising single-material platform for Majorana braiding at a relatively high temperature. Copyright © 2019, The Authors. All rights reserved.

关键词： Iron-based Superconductors

Charge-Density-Wave Transitions of Dirac Fermions Coupled to Phonons

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Physical Review Letters 2019年第7期122卷 077601-077601页

作者： Chuang Chen Xiao Yan Xu Zi Yang Meng Martin Hohenadler 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 Department of Physics Hong Kong University of Science and Technology Clear Water Bay Hong Kong China CAS Center of Excellence in Topological Quantum Computation and School of Physical Sciences University of Chinese Academy of Sciences Beijing 100190 China Songshan Lake Materials Laboratory Dongguan Guangdong 523808 China Institut für Theoretische Physik und Astrophysik Universität Würzburg 97074 Würzburg Germany

The spontaneous generation of charge-density-wave order in a Dirac fermion system via the natural mechanism of electron-phonon coupling is studied in the framework of the Holstein model on the honeycomb lattice. Using two independent and unbiased quantum Monte Carlo methods, the phase diagram as a function of temperature and coupling strength is determined. It features a quantum critical point as well as a line of thermal critical points. Finite-size scaling appears consistent with fermionic Gross-Neveu-Ising universality for the quantum phase transition and bosonic Ising universality for the thermal phase transition. The critical temperature has a maximum at intermediate couplings. Our findings motivate experimental efforts to identify or engineer Dirac systems with sufficiently strong and tunable electron-phonon coupling.

关键词： Charge density waves Electron-phonon coupling Metal-insulator transition Phase diagrams Phase transitions Quantum phase transitions Graphene Quantum Monte Carlo

A recursive algebraic coloring technique for hardware-efficient symmetric sparse matrix-vector multiplication

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arXiv 2019年

作者： Alappat, Christie Hager, Georg Schenk, Olaf Thies, Jonas Basermann, Achim Bishop, Alan R. Fehske, Holger Wellein, Gerhard Department of Computer Science Friedrich-Alexander-Universitat Erlangen-Nurnberg Germany Erlangen Regional Computing Center Friedrich-Alexander-Universität Erlangen-Nürnberg Germany Institute of Computational Science Università della Svizzera Italiana Simulation and Software Technology German Aerospace Center Theory Simulation and Computation Los Alamos National Laboratory Institute of Physics University of Greifswald

The symmetric sparse matrix-vector multiplication (SymmSpMV) is an important building block for many numerical linear algebra kernel operations or graph traversal applications. Parallelizing SymmSpMV on today's multicore platforms with up to 100 cores is di-cult due to the need to manage *** updates on the result vector. Coloring approaches can be used to solve this problem without data duplication, but existing coloring algorithms do not take load balancing and deep memory hierarchies into account, hampering scalability and full-chip performance. In this work, we propose the recursive algebraic coloring engine (RACE), a novel coloring algorithm and open-source library implementation, which eliminates the shortcomings of previous coloring methods in terms of hardware e-ciency and parallelization overhead. We describe the level construction, distance-k coloring, and load balancing steps in RACE, use it to parallelize SymmSpMV, and compare its performance on 31 sparse matrices with other state-of-the-art coloring techniques and Intel MKL on two modern multicore processors. RACE outperforms all other approaches substantially and behaves in accordance with the roofline model. Outliers are discussed and analyzed in detail. While we focus on SymmSpMV in this paper, our algorithm and *** is applicable to any sparse matrix operation with data dependencies that can be resolved by distance-k coloring. Copyright © 2019, The Authors. All rights reserved.

关键词： Coloring

An ab-initio effective solid state photoluminescence by frequency constraint of cluster calculation

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arXiv 2019年

作者： Karim, Akib Lyskov, Igor Russo, Salvy P. Peruzzo, Alberto Quantum Photonics Laboratory School of Engineering RMIT University MelbourneVIC3000 Australia Centre for Quantum Computation and Communication Technology School of Engineering RMIT University MelbourneVIC3000 Australia ARC Centre of Excellence in Exciton Science School of Science RMIT University MelbourneVIC3001 Australia Chemical and Quantum Physics School of Science RMIT University MelbourneVIC3001 Australia

Measuring the photoluminescence of defects in crystals is a common experimental technique for analysis and identification. However, current theoretical simulations typically require the simulation of a large number of atoms to eliminate finite size effects, which discourages computationally expensive excited state methods. We show how to extract the room-temperature photoluminescence spectra of defect centres in bulk from an ab-initio simulation of a defect in small clusters. The finite size effect of small clusters manifests as strong coupling to low frequency vibrational modes. We find that removing vibrations below a cutoff frequency determined by constrained optimization returns the main features of the solid state photoluminescence spectrum. This strategy is illustrated for an NV− defect in diamond, presenting a connection between defects in solid state and clusters;the first vibrationally resolved ab-initio photoluminescence spectrum of an NV− defect in a nanodiamond;and an alternative technique for simulating photoluminescence for solid state defects utilizing more accurate excited state methods. Copyright © 2019, The Authors. All rights reserved.

关键词： Photoluminescence spectroscopy