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Dipolar Weyl semimetals

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arXiv 2022年

作者： Tyner, Alexander C. Sur, Shouvik Graduate Program in Applied Physics Northwestern University EvanstonIL60208 United States Department of Physics and Astronomy Rice University HoustonTX77005 United States

In Weyl semimetals, Weyl points act as monopoles and antimonopoles of the Berry curvature, with a monopole-antimonopole pair producing a net zero Berry flux. When inversion symmetry is preserved, the two-dimensional (2D) planes that separate a monopole-antimonopole pair of Weyl points carry quantized Berry flux. In this work, we introduce a class of symmetry-protected Weyl semimetals which host monopole-antimonopole pairs of Weyl points that generate a dipolar Berry flux. Thus, both monopolar and dipolar Berry fluxes coexist in the Brillouin zone, which results in two distinct types of topologically non-trivial planes separating the Weyl points, carrying either a quantized monopolar or a quantized dipolar flux. We construct a topological invariant – the staggered Chern number – to measure the latter, and employ it to topologically distinguish between various Weyl points. Finally, through a minimal two-band model, we investigate physical signatures of bulk topology, including surface Fermi arcs, zero-energy hinge states, and response to insertion of a π-flux vortex. © 2022, CC BY-NC-SA.

关键词： Fruits

Spin-charge separation and quantum spin Hall effect of β-bismuthene

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arXiv 2022年

作者： Tyner, Alexander C. Goswami, Pallab Graduate Program in Applied Physics Northwestern University EvanstonIL60208 United States Department of Physics and Astronomy Northwestern University EvanstonIL60208 United States

Field theory arguments suggest the possibility of Z-classification of quantum spin Hall effect with magnetic flux tubes, that cause separation of spin and charge degrees of freedom, and pumping of spin or Kramers pair. However, the proof of principle demonstration of spin-charge separation is yet to be accomplished for realistic, ab initio band structures of spin-orbit-coupled materials, lacking spin-conservation law. In this work, we perform thought experiments with magnetic flux tubes on β-bismuthene to demonstrate spin-charge separation, and quantized pumping of spin for three insulating states that can be accessed by tuning filling fractions. With a combined analysis of momentum-space topology and real-space response, we identify important role of topologically non-trivial bands, supporting even integer winding numbers, which cannot be inferred from symmetry-based indicators. Our work sets a new standard for prediction of two-dimensional, quantum spin-Hall materials, based on precise bulk invariant and universal topological response. Copyright © 2022, The Authors. All rights reserved.

关键词： Separation

Part I: Staggered index and 3D winding number of Kramers-degenerate bands

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arXiv 2021年

For three-dimensional (3D) crystalline insulators, preserving space-inversion (P) and time-reversal (T ) symmetries, the third homotopy class of two-fold, Kramers-degenerate bands is described by a 3D winding number n3,j ∈ Z, where j is the band index. It governs space group symmetry-protected, instanton or tunneling configurations of SU(2) Berry connection, and the quantization of magneto-electric coefficient θj = n3,jπ. We show that |n3,j| for realistic, ab initio band structures can be identified from a staggered symmetry-indicator κAF,j ∈ Z and the gauge-invariant spectrum of SU(2) Wilson loops. The procedure is elucidated for 4-band and 8-band tight-binding models and ab initio band structure of Bi, which is a Z2-trivial, higher-order, topological crystalline insulator. When the tunneling is protected by Cnh and Dnh point groups, the proposed method can also identify the signed winding number n3,j. Our analysis distinguishes between magneto-electrically trivial (θ = 0) and non-trivial (θ = 2sπ, with s ≠ 0) topological crystalline insulators. In Part II, we demonstrate Z-classification of θ by computing induced electric charge (Witten effect) on magnetic Dirac monopoles. Copyright © 2021, The Authors. All rights reserved.

关键词： Topology

Solitons and real-space screening of bulk topology of quantum materials

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arXiv 2023年

Recent years have seen multiple high-throughput studies reveal an immense number of topological materials through use of symmetry indicators. Despite this success, three-dimensional topological insulators (TIs) admitting a band-gap larger than Bi2Se3 and two-dimensional TIs admitting a band gap larger than β-bismuthene, two of the originally proposed TIs, remain extremely rare. Simultaneously, a significant effort has been made to understand and identify topological phases "invisible" to symmetry indicators. Such phases offer a unique opportunity to expand the search for a large band-gap TI, however their identification requires sophisticated probes of bulk topology. Magnetic flux tubes or vortices have emerged as one such probe in two-dimensions when inserted into the bulk. In this work, we develop an automated workflow to perform vortex insertion and apply it to a current database of high-quality, experimentally realized, two-dimensional insulators. The results reveal multiple novel two-dimensional topological insulators supporting large bands gaps, including the 1H-MX2 (M=Mo,W) and (X=S,Se,Te) family of transition metal dichalcogenides. Our work has broad implications for current theoretical and experimental efforts to employ these materials in superconducting and Moire systems. Copyright © 2023, The Authors. All rights reserved.

关键词： Energy gap

Part II: Witten effect and Z-classification of axion angle θ = nπ

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arXiv 2022年

The non-trivial third homotopy class of three-dimensional topological insulators leads to quantized, magnetoelectric coefficient or axion angle θ = nπ, with n ∈ Z. In Part I, we developed tools for computing n from a staggered symmetry-indicator κAF,j and Wilson loops of non-Abelian, Berry connection in momentum-space, which clearly distinguished between magneto-electrically trivial (n = 0), and non-trivial (n = 2s) topological crystalline insulators. In this work, we perform Z-classification of real-space, topological response or θ by carrying out thought experiments with magnetic, Dirac monopoles. We demonstrate this for non-magnetic and magnetic topological insulators by computing induced electric charge on monopoles or Witten effect. We show that both first- and higher- order topological insulators can exhibit quantized, magneto-electric response, irrespective of the presence of gapless surface-states, and corner-states. Special attention is paid to the response of octupolar higher-order topological insulator, which was originally predicted to be magneto-electrically trivial. The important roles of fermion zero-modes, CP, and flavor symmetries are critically addressed. Our work outlines a unified theoretical framework for addressing dc topological response and topological quantum phase transitions, which cannot be reliably predicted by symmetry-based classification scheme. Copyright © 2022, The Authors. All rights reserved.

关键词： Topological insulators

Structure and dynamics of highly charged heavy ions studied with the electron beam ion trap in Tokyo

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Hyperfine Interactions 2011年第1期199卷 123-130页

作者： Nakamura, Nobuyuki Hu, Zhimin Watanabe, Hirofumi Li, Yueming Kato, Daiji Currell, Fred J. Tong, Xiao-Min Watanabe, Tsutomu Ohtani, Shunsuke Institute for Laser Science The University of Electro-Communications 1-5-1 Chofugaoka Chofu Tokyo 182-8585 Japan Chubu University 1200 Matsumoto-cho Kasugai-shi Aichi 487-8501 Japan Institute of Applied Physics and Computational Mathematics P.O.Box 8009 Beijing 100088 China National Institute for Fusion Science 322-6 Oroshi-cho Toki Gifu 509-5292 Japan Centre for Plasma Physics School of Mathematics and Physics Queen's University Belfast Belfast BT7 1NN United Kingdom Doctoral Program in Materials Science Graduate School of Pure and Applied Sciences University of Tsukuba Tsukuba Ibaraki 305-8573 Japan

In this paper, we present the structure and the dynamics of highly charged heavy ions studied through dielectronic recombination (DR) observations performed with the Tokyo electron beam ion trap. By measuring the energy dependence of the ion abundance ratio in the trap at equilibrium, we have observed DR processes for open shell systems very clearly. Remarkable relativistic effects due to the generalized Breit interaction have been clearly shown in DR for highly charged heavy ions. We also present the first result for the coincidence measurement of two photons emitted from a single DR event. © 2011 Springer Science+Business Media B.V.

关键词： Heavy ions

Mechanistic insights of evaporation-induced actuation in supramolecular crystals (Sept, 10.1038/s41563-020-0799-0, 2020)

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NATURE MATERIALS 2021年第3期20卷 434-434页

作者： Piotrowska, Roxana Hesketh, Travis Wang, Haozhen Martin, Alan R. G. Bowering, Deborah Zhang, Chunqiu Hu, Chunhua T. McPhee, Scott A. Wang, Tong Park, Yaewon Singla, Pulkit McGlone, Thomas Florence, Alastair Tuttle, Tell Ulijn, Rein V. Chen, Xi Advanced Science Research Center (ASRC) at the Graduate Center of the City University of New York New York NY USA PhD Program in Chemistry The Graduate Center of the City University of New York New York NY USA Department of Pure and Applied Chemistry University of Strathclyde Glasgow UK PhD Program in Physics The Graduate Center of the City University of New York New York NY USA EPSRC Continuous Manufacturing and Crystallisation Future Research Hub c/o Strathclyde Institute of Pharmacy and Biomedical Sciences Technology Innovation Centre University of Strathclyde Glasgow UK Department of Chemistry New York University New York NY USA Department of Chemistry and Biochemistry Hunter College City University of New York New York NY USA Department of Chemical Engineering The City College of New York New York NY USA

A Correction to this paper has been published: https://***/10.1038/s41563-021-00950-3.

关键词： Condensed-matter physics Materials science Soft materials

Optical mapping of transcriptional factor binding sites on single DNA molecules using nanofluidic devices

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Optical mapping of transcriptional factor binding sites on s...

16th International Conference on Miniaturized Systems for Chemistry and Life Sciences, MicroTAS 2012

作者： Sriram, K.K. Yeh, Jia-Wei Lin, Yii-Lih Chang, Yi-Ren Chou, Chia-Fu Institute of Physics Academia Sinica Taiwan Nanoscience and Technology/Taiwan International Graduate Program Academia Sinica Taiwan Department of Engineering and System Sciences National Tsing Hua University Taiwan Genomic Research Center Academia Sinica Taiwan Research Center for Applied Sciences Academia Sinica Taiwan

ISBN: (纸本)9780979806452

Transcriptional factors (TF) are proteins that bind to specific bases of DNA using DNA binding domains to carry out the process of transcription. Identification of TF binding sites is essential for understanding the regulatory circuits that control cellular processes such as cell division and differentiation as well as metabolic and physiological balance [1]. In this work, we deploy a proof-of-concept method adopting bio-conjugation, nanofluidic devices and single molecule techniques for direct mapping of TF binding sites on field stretched single DNA molecules. Here we demonstrated a simple and robust system for TF binding site identification, complementary to the existing techniques practiced in this field.

关键词： Binding sites

Chiral quasi-bound states in the continuum

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arXiv 2020年

作者： Overvig, Adam Yu, Nanfang Alù, Andrea Photonics Initiative Advanced Science Research Center The Graduate Center The City University of New York United States Department of Applied Physics and Applied Mathematics Columbia University United States Physics Program Graduate Center City University of New York United States

Quasi-bound states in the continuum (q-BICs) are resonant states of suitably tailored nanostructures with long optical lifetimes controlled by symmetry-breaking perturbations. While in planarized ultrathin devices the resulting Fano resonance is limited to linear polarization, we show here that chiral perturbations extend q-BIC concepts to arbitrary elliptical polarizations. Using geometric phase engineering, we realize metasurfaces with ultrasharp Fano spectral features that can shape the impinging wavefront with near-unity efficiency, while at the same time precisely filtering their spectral content. Copyright © 2020, The Authors. All rights reserved.

关键词： Polarization