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Tunable double Weyl phonons driven by chiral point group symmetry

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Physical Review B 2021年第10期103卷 104101-104101页

作者： Y. J. Jin Z. J. Chen X. L. Xiao H. Xu Department of Physics & Institute for Quantum Science and Engineering Southern University of Science and Technology Shenzhen 518055 People's Republic of China Department of Physics the University of Hong Kong Pokfulam Road Hong Kong People's Republic of China Department of Physics South China University of Technology Guangzhou 510640 People's Republic of China Institute for Structure and Function & Department of physics Chongqing University Chongqing 400044 People's Republic of China Guangdong Provincial Key Laboratory of Computational Science and Material Design & Shenzhen Key Laboratory for Advanced Quantum Functional Materials and Devices Southern University of Science and Technology Shenzhen 518055 People's Republic of China

Different from spin-12 Weyl points which are robust due to the protection of topology, the unconventional chiral quasiparticles usually require extra crystalline symmetries for their existence, indicating that such quasiparticles are sensitive to perturbation. Herein, we present that the spin-1 Weyl can transform into quadratic Weyl phonons depending on symmetry variation. Specifically, the spin-1 Weyl nodes arisen from three-dimensional (3D) irreducible representations (IRs) of chiral point groups, O(432) or T(23), are verified to split into quadratic Weyl points if symmetry breaking decomposes 3D IRs into two-dimensional IRs. Symmetry analysis and low-energy effective models are performed to identify the splitting mechanisms. The evolution of Berry curvature and surface states driven by symmetry breaking is obtained in real materials. Our work not only builds the connection between double Weyl phonons but also offers guidance for exploring the transition among unconventional quasiparticles.

关键词： Phonons Topological phase transition Topological materials Weyl semimetal First-principles calculations k dot p method

Effect of Synaptic Heterogeneity on Neuronal Coordination

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PRX Life 2024年第1期2卷 013013-013013页

作者： Moritz Layer Moritz Helias David Dahmen Institute of Neuroscience and Medicine (INM-6) and Institute for Advanced Simulation (IAS-6) and JARA-Institute Brain Structure-Function Relationships (INM-10) Jülich Research Centre Jülich Germany RWTH Aachen University Aachen Germany Department of Physics Faculty 1 RWTH Aachen University Aachen Germany

Recent advancements in measurement techniques have resulted in an increasing amount of data on neural activities recorded in parallel, revealing largely heterogeneous correlation patterns across neurons. Yet, the mechanistic origin of this heterogeneity is largely unknown because existing theoretical approaches linking structure and dynamics in neural circuits are restricted to population-averaged connectivity and activity. Here we present a systematic inclusion of heterogeneity in network connectivity to derive quantitative predictions for neuron-resolved covariances and their statistics in spiking neural networks. Our study shows that the heterogeneity in covariances is not a result of variability in single-neuron firing statistics but stems from the ubiquitously observed sparsity and variability of connections in brain networks. Linear-response theory maps these features to the effective connectivity between neurons, which in turn determines neuronal covariances. Beyond-mean-field tools reveal that synaptic heterogeneity modulates the variability of covariances and thus the complexity of neuronal coordination across many orders of magnitude.

关键词： Collective behavior in networks Network stability Network structure Neuronal network activity Spiking neurons Statistical field theory Biological neural networks Disordered systems Random graphs Mean field theory Neuronal network models Replica methods Spiking neuron models

Electric and magnetic fields tuned spin-polarized topological phases in two-dimensional ferromagnetic MnBi4Te7

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arXiv 2021年

作者： Xiao, Shi Xiao, Xiaoliang Zhan, Fangyang Fan, Jing Wu, Xiaozhi Wang, Rui Institute for Structure and Function and Department of Physics Chongqing University Chongqing400044 China Chongqing Key Laboratory for Strongly Coupled Physics Chongqing400044 China Center for Computational Science and Engineering Southern University of Science and Technology Shenzhen518055 China Center for Quantum Materials and Devices Chongqing University Chongqing400044 China

Applying electric or magnetic fields is widely used to not only create and manipulate topological states but also facilitate their observations in experiments. In this work, we show by first-principles calculations and topological analysis that the time-reversal (TR) symmetry-broken quantum spin Hall (QSH) state emerges in a two-dimensional (2D) ferromagnetic MnBi4Te7monolayer. This TR-symmetry broken QSH phase possesses a highly tunable nontrivial band gap under an external electric field (or tuning interlayer distance). Furthermore, based on the Wannier-function-based tight-binding approach, we reveal that a topological phase transition from the TR-symmetry broken QSH phase to the quantum anomalous Hall (QAH) phase occurs with the increase of magnetic fields. Besides, we also find that a reverse electric fields can facilitate the realization of QAH phase. Our work not only uncovers the ferromagnetic topological properties the MnBi4Te7monolayer tuned by electric and magnetic fields, but also can stimulate further applications to spintronics and topological devices. Copyright © 2021, The Authors. All rights reserved.

关键词： Ferromagnetism

Type-II nodal line fermions in the Z2 topological semimetals AV6Sb6 (A=K, Rb, and Cs) with a kagome bilayer

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Physical Review B 2021年第24期104卷 245128-245128页

作者： Y. Yang R. Wang M.-Z. Shi Z. Wang Z. Xiang X.-H. Chen Hefei National Laboratory for Physical Sciences at Microscale and Department of Physics and Key Laboratory of Strongly-Couple Quantum Matter Physics Chinese Academy of Sciences University of Science and Technology of China Hefei Anhui 230026 China Institute for Structure and Function and Department of Physics and Center for Quantum Materials and Devices Chongqing University Chongqing 400044 China Chongqing Key Laboratory for Strongly Coupled Physics Chongqing 400044 China CAS Center for Excellence in Superconducting Electronics (CENSE) Shanghai 200050 China CAS Center for Excellence in Quantum Information and Quantum Physics Hefei Anhui 230026 China Collaborative Innovation Center of Advanced Microstructures Nanjing University Nanjing 210093 China

The recently discovered layered kagome metals AV3Sb5 (A=K, Rb, and Cs) attract intensive interest due to their intertwining with superconductivity, charge-density-wave state, and nontrivial band topology. In this work, we show by first-principles calculations and symmetry arguments that unconventional type-II Dirac nodal line fermions close to the Fermi level are present in another latest class of experimentally synthesized kagome compounds AV6Sb6 (A=K, Rb, and Cs). These compounds possess a unique kagome (V3Sb)2 bilayer that dominates their electronic and topological properties, instead of the kagome V3Sb monolayer in AV3Sb5. Crystal symmetry guarantees that the type-II Dirac nodal lines with quantized Berry phase lie in reflection-invariant planes of the Brillouin zone. We further reveal that the type-II Dirac nodal lines remain nearly intact in the presence of spin-orbital coupling and can be categorized as a Z2 classification. The findings establish AV6Sb6 as a class of new fascinating prototypes, which will extend the knowledge of interplay between unconventionally topological fermions and exotic quantum ordered states in kagome systems.

关键词： Electronic structure Symmetry protected topological states Topological insulators Topological materials Kagome lattice Node-line semimetals Semimetals Topological superconductors First-principles calculations Wannier function methods k dot p method

Catalogue of topological phonon materials

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arXiv 2022年

作者： Xu, Yuanfeng Vergniory, M.G. Ma, Da-Shuai Mañes, Juan L. Song, Zhi-Da Bernevig, B. Andrei Regnault, Nicolas Elcoro, Luis Department of Physics Princeton University PrincetonNJ08544 United States Center for Correlated Matter School of Physics Zhejiang University Hangzhou310058 China Donostia International Physics Center P. Manuel de Lardizabal 4 Donostia-San Sebastian20018 Spain Max Planck Institute for Chemical Physics of Solids Dresden01309 Germany Institute for Structure and Function Department of Physics Chongqing Key Laboratory for Strongly Coupled Physics Chongqing University Chongqing400044 China Department of Physics University of the Basque Country UPV/EHU Apartado 644 Bilbao48080 Spain International Center for Quantum Materials School of Physics Peking University Beijing100871 China IKERBASQUE Basque Foundation for Science Bilbao Spain Laboratoire de Physique de l’Ecole normale supérieure ENS Université PSL CNRS Sorbonne Université Université Paris-Diderot Sorbonne Paris Cité Paris75005 France

Phonons play a crucial role in many properties of solid state systems, such as thermal and electrical conductivity, neutron scattering and associated effects or superconductivity. Hence, it is expected that topological phonons will also lead to rich and unconventional physics and the search of materials hosting topological phonons becomes a priority in the field. In electronic crystalline materials, a large part of the topological properties of Bloch states can be indicated by their symmetry eigenvalues in reciprocal space. This has been adapted to the high-throughput calculations of topological materials, and more than half of the stoichiometric materials on the databases are found to be topological insulators or semi-metals. Based on the existing phonon materials databases, here we have performed the first catalogue of topological phonon bands for more than ten thousand three-dimensional crystalline materials. Using topological quantum chemistry, we calculate the band representations, compatibility relations, and band topologies of each isolated set of phonon bands for the materials in the phonon databases. We have also calculated the real space invariants for all the topologically trivial bands and classified them as atomic and obstructed atomic bands. In particular, surface phonon modes (dispersion) are calculated on different cleavage planes for all the materials. Remarkably, we select more than one thousand "ideal" non-trivial phonon materials to fascinate the future experimental studies. All the data-sets obtained in the the high-throughput calculations are used to build a Topological Phonon Database. Copyright © 2022, The Authors. All rights reserved.

关键词： Database systems

Photoinduced quantum anomalous hall states in the topological anderson insulator

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arXiv 2021年

作者： Ning, Zhen Zheng, Baobing Xu, Dong-Hui Wang, Rui Institute for Structure and Function Department of Physics Chongqing University Chongqing400044 China Chongqing Key Laboratory for Strongly Coupled Physics Chongqing400044 China College of Physics and Optoelectronic Technology Advanced Titanium Alloys and Functional Coatings Cooperative Innovation Center Baoji University of Arts and Sciences Baoji721016 China Department of Physics Hubei University Wuhan430062 China Center for Quantum Materials and Devices Chongqing University Chongqing400044 China

The realization of the quantum anomalous Hall (QAH) effect without magnetic doping attracts intensive interest since magnetically doped topological insulators usually possess inhomogeneity of ferromagnetic order. Here, we propose a different strategy to realize intriguing QAH states aris- ing from the interplay of light and non-magnetic disorder in two-dimensional topologically trivial systems. By combining the Born approximation and Floquet theory, we show that a time-reversal invariant disorder-induced topological insulator, known as the topological Anderson insulator (TAI), would evolve into a time-reversal broken TAI and then into a QAH insulator by shining circularly polarized light. We utilize spin and charge Hall conductivities, which can be measured in experi- ments directly, to distinguish these three different topological phases. This work not only offers an exciting opportunity to realize the high-temperature QAH effect without magnetic orders, but also is important for applications of topological states to spintronics. Copyright © 2021, The Authors. All rights reserved.

关键词： Electric insulators

Transient Chaotic Dimensionality Expansion by Recurrent Networks

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Physical Review X 2021年第2期11卷 021064-021064页

作者： Christian Keup Tobias Kühn David Dahmen Moritz Helias Institute of Neuroscience and Medicine (INM-6) and Institute for Advanced Simulation (IAS-6) and JARA Institut Brain Structure-Function Relationships (INM-10) Jülich Research Centre Jülich Germany RWTH Aachen University Aachen Germany Laboratoire de Physique de l’ENS Laboratoire MSC de l’Université de Paris CNRS Paris France Department of Physics Faculty 1 RWTH Aachen University Aachen Germany

Neurons in the brain communicate with spikes, which are discrete events in time and value. functional network models often employ rate units that are continuously coupled by analog signals. Is there a qualitative difference implied by these two forms of signaling? We develop a unified mean-field theory for large random networks to show that first- and second-order statistics in rate and binary networks are in fact identical if rate neurons receive the right amount of noise. Their response to presented stimuli, however, can be radically different. We quantify these differences by studying how nearby state trajectories evolve over time, asking to what extent the dynamics is chaotic. Chaos in the two models is found to be qualitatively different. In binary networks, we find a network-size-dependent transition to chaos and a chaotic submanifold whose dimensionality expands stereotypically with time, while rate networks with matched statistics are nonchaotic. Dimensionality expansion in chaotic binary networks aids classification in reservoir computing and optimal performance is reached within about a single activation per neuron; a fast mechanism for computation that we demonstrate also in spiking networks. A generalization of this mechanism extends to rate networks in their respective chaotic regimes.

关键词： Fluctuations & noise Neural encoding Neuronal networks Statistical field theory Chaos & nonlinear dynamics Dynamical mean field theory Ising model Langevin equation

Large-Deviation Approach to Random Recurrent Neuronal Networks: Parameter Inference and Fluctuation-Induced Transitions

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Physical Review Letters 2021年第15期127卷 158302-158302页

作者： Alexander van Meegen Tobias Kühn Moritz Helias Institute of Neuroscience and Medicine (INM-6) and Institute for Advanced Simulation (IAS-6) and JARA-Institute Brain Structure-Function Relationships (INM-10) Jülich Research Centre 52428 Jülich Germany Institute of Zoology University of Cologne 50674 Cologne Germany Department of Physics Faculty 1 RWTH Aachen University 52074 Aachen Germany Laboratoire de Physique de l’Ecole Normale Supérieure ENS Université PSL CNRS Sorbonne Université Université de Paris F-75005 Paris France

We here unify the field-theoretical approach to neuronal networks with large deviations theory. For a prototypical random recurrent network model with continuous-valued units, we show that the effective action is identical to the rate function and derive the latter using field theory. This rate function takes the form of a Kullback-Leibler divergence which enables data-driven inference of model parameters and calculation of fluctuations beyond mean-field theory. Lastly, we expose a regime with fluctuation-induced transitions between mean-field solutions.

关键词： Neuronal networks Statistical field theory Dynamical mean field theory Information theory Large deviation & rare event statistics

Floquet valley-polarized quantum anomalous hall state in nonmagnetic heterobilayers

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arXiv 2021年

作者： Zhan, Fangyang Ning, Zhen Gan, Li-Yong Zheng, Baobing Fan, Jing Wang, Rui Institute for Structure and Function Department of Physics Chongqing University Chongqing400044 China Chongqing Key Laboratory for Strongly Coupled Physics Chongqing400044 China Center for Computational Science and Engineering Southern University of Science and Technology Shenzhen518055 China Center for Quantum Materials and Devices Chongqing University Chongqing400044 China College of Physics and Optoelectronic Technology Baoji University of Arts and Sciences Baoji721016 China

The valley-polarized quantum anomalous Hall (VQAH) state, which forwards a strategy for combining valleytronics and spintronics with nontrivial topology, attracts intensive interest in condensedmatter physics. So far, the explored VQAH states have still been limited to magnetic systems. Here, using the low-energy effective model and Floquet theorem, we propose a different mechanism to realize the Floquet VQAH state in nonmagnetic heterobilayers under light irradiation. We then realize this proposal via first-principles calculations in transition metal dichalcogenide heterobilayers, which initially possess the time-reversal invariant valley quantum spin Hall (VQSH) state. By irradiating circularly polarized light, the time-reversal invariant VQSH state can evolve into the VQAH state, behaving as an optically switchable topological spin-valley filter. These findings not only offer a rational scheme to realize the VQAH state without magnetic orders, but also pave a fascinating path for designing topological spintronic and valleytronic devices. Copyright © 2021, The Authors. All rights reserved.

关键词： Landforms