scholarly journals Non-Hermitian route to higher-order topology in an acoustic crystal

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
He Gao ◽  
Haoran Xue ◽  
Zhongming Gu ◽  
Tuo Liu ◽  
Jie Zhu ◽  
...  
Keyword(s):  
Higher Order ◽  
Order Topology ◽  
Topological Phases ◽  
Edge States ◽  
Experimental Realization ◽  
Artificial Materials ◽  
Intrinsic Loss ◽  
Topological Phases Of Matter ◽  
Hierarchical Features ◽  
Nontrivial Topology

AbstractTopological phases of matter are classified based on their Hermitian Hamiltonians, whose real-valued dispersions together with orthogonal eigenstates form nontrivial topology. In the recently discovered higher-order topological insulators (TIs), the bulk topology can even exhibit hierarchical features, leading to topological corner states, as demonstrated in many photonic and acoustic artificial materials. Naturally, the intrinsic loss in these artificial materials has been omitted in the topology definition, due to its non-Hermitian nature; in practice, the presence of loss is generally considered harmful to the topological corner states. Here, we report the experimental realization of a higher-order TI in an acoustic crystal, whose nontrivial topology is induced by deliberately introduced losses. With local acoustic measurements, we identify a topological bulk bandgap that is populated with gapped edge states and in-gap corner states, as the hallmark signatures of hierarchical higher-order topology. Our work establishes the non-Hermitian route to higher-order topology, and paves the way to exploring various exotic non-Hermiticity-induced topological phases.

scholarly journals Confinement Properties of the 3D Topological Insulators Bi₂Se₃, Bi₂Te₃, and Sb₂Te₃

2021 ◽  
Author(s):  
◽  
Markus Kotulla
Keyword(s):  
Magnetic Field ◽  
Topological Insulators ◽  
Surface States ◽  
Cold Atom ◽  
Zeeman Splitting ◽  
Dirac Fermion ◽  
Topological Phases ◽  
Edge States ◽  
Experimental Realization ◽  
Band Inversion

<p>Recent discoveries have spurred the theoretical prediction and experimental realization of novel materials that have topological properties arising from band inversion. Such topological insulators have conductive surface or edge states but are insulating in the bulk. How the signatures of topological behavior evolve when the system size is reduced is noteworthy from both a fundamental and an application-oriented point of view, as such understanding may form the basis for tailoring systems to be in specific topological phases. This thesis investigates the softly confined topological insulator family of Bi₂Se₃ and its properties when subjected to an in-plane magnetic field. The model system provides a useful platform for systematic study of the transition between the normal and the topological phases, including the development of band inversion and the formation of massless-Dirac-fermion surface states. The effects of bare size quantization, two-dimensional-subband mixing, and electron-hole asymmetry are disentangled and their corresponding physical consequences elucidated.  When a magnetic field is present, it is found that the Dirac cone which is formed in surface states, splits into two cones separated in momentum space and that these cones exhibit properties of Weyl fermions. The effective Zeeman splitting is much larger for the surface states than for the bulk states. Furthermore, the g-factor of the surface states depends on the size of the material. The mathematical model presented here may be realizable experimentally in the frame of optical lattices in ultra cold atom gases.</p>

Synopsis and outlook

2021 ◽  
pp. 263-268
Author(s):  
Falko P. Netzer ◽  
Claudine Noguera
Keyword(s):  
Scientific Activity ◽  
Simulation Methods ◽  
Topological Phases ◽  
Oxide Materials ◽  
Experimental Realization ◽  
Nano Oxide ◽  
Highly Correlated ◽  
Topological Phases Of Matter ◽  
Structure Engineering ◽  
Opening Up

The synopsis part of this last chapter gives a brief summary of the book content. The outlook attempts to identify future areas of scientific activity, in which according to the authors´ visions nano-oxide materials may promote new developments. Among them are the controlled synthesis of oxide nanosheets and the experimental realization of oxide nanoribbons. The preparation of well-defined oxide heterostructures may reveal novel emergent states and new topological phases of matter. Mixed nano-oxides will be of interest for band structure engineering and to adjust band edges for photochemical reactivity. Programmable defect chemistry may open up new selective pathways for catalytic reactions. In parallel with experimental progress, advanced theoretical and simulation methods will take advantage of the ever-increasing computer power to tackle highly correlated materials and allow highthroughput computing. The interaction of nano-oxides with biological systems has great potential for opening up new avenues in the biotechnological area.

scholarly journals Confinement Properties of the 3D Topological Insulators Bi₂Se₃, Bi₂Te₃, and Sb₂Te₃

2021 ◽  
Author(s):  
◽  
Markus Kotulla
Keyword(s):  
Magnetic Field ◽  
Topological Insulators ◽  
Surface States ◽  
Cold Atom ◽  
Zeeman Splitting ◽  
Dirac Fermion ◽  
Topological Phases ◽  
Edge States ◽  
Experimental Realization ◽  
Band Inversion

<p>Recent discoveries have spurred the theoretical prediction and experimental realization of novel materials that have topological properties arising from band inversion. Such topological insulators have conductive surface or edge states but are insulating in the bulk. How the signatures of topological behavior evolve when the system size is reduced is noteworthy from both a fundamental and an application-oriented point of view, as such understanding may form the basis for tailoring systems to be in specific topological phases. This thesis investigates the softly confined topological insulator family of Bi₂Se₃ and its properties when subjected to an in-plane magnetic field. The model system provides a useful platform for systematic study of the transition between the normal and the topological phases, including the development of band inversion and the formation of massless-Dirac-fermion surface states. The effects of bare size quantization, two-dimensional-subband mixing, and electron-hole asymmetry are disentangled and their corresponding physical consequences elucidated.  When a magnetic field is present, it is found that the Dirac cone which is formed in surface states, splits into two cones separated in momentum space and that these cones exhibit properties of Weyl fermions. The effective Zeeman splitting is much larger for the surface states than for the bulk states. Furthermore, the g-factor of the surface states depends on the size of the material. The mathematical model presented here may be realizable experimentally in the frame of optical lattices in ultra cold atom gases.</p>

scholarly journals Observation of a symmetry-protected topological phase of interacting bosons with Rydberg atoms

Science ◽  
2019 ◽  
Vol 365 (6455) ◽  
pp. 775-780 ◽  
Author(s):  
Sylvain de Léséleuc ◽  
Vincent Lienhard ◽  
Pascal Scholl ◽  
Daniel Barredo ◽  
Sebastian Weber ◽  
...  
Keyword(s):  
Optical Tweezers ◽  
Ground States ◽  
Hard Core ◽  
Topological Phases ◽  
Topological Phase ◽  
Edge States ◽  
Many Body ◽  
Experimental Realization ◽  
Many Body Systems ◽  
Symmetry Protected

The concept of topological phases is a powerful framework for characterizing ground states of quantum many-body systems that goes beyond the paradigm of symmetry breaking. Topological phases can appear in condensed-matter systems naturally, whereas the implementation and study of such quantum many-body ground states in artificial matter require careful engineering. Here, we report the experimental realization of a symmetry-protected topological phase of interacting bosons in a one-dimensional lattice and demonstrate a robust ground state degeneracy attributed to protected zero-energy edge states. The experimental setup is based on atoms trapped in an array of optical tweezers and excited into Rydberg levels, which gives rise to hard-core bosons with an effective hopping generated by dipolar exchange interaction.

scholarly journals Topological gaps by twisting

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Matheus I. N. Rosa ◽  
Massimo Ruzzene ◽  
Emil Prodan
Keyword(s):  
Magnetic Field ◽  
Quantum Hall Effect ◽  
Twist Angle ◽  
Quantum Hall ◽  
Topological Phases ◽  
Edge States ◽  
Layered Systems ◽  
Virtual Laboratories ◽  
Higher Dimensional ◽  
Chern Numbers

AbstractTwisted bilayered systems such as bilayered graphene exhibit remarkable properties such as superconductivity at magic angles and topological insulating phases. For generic twist angles, the bilayers are truly quasiperiodic, a fact that is often overlooked and that has consequences which are largely unexplored. Herein, we uncover that twisted n-layers host intrinsic higher dimensional topological phases, and that those characterized by second Chern numbers can be found in twisted bi-layers. We employ phononic lattices with interactions modulated by a second twisted lattice and reveal Hofstadter-like spectral butterflies in terms of the twist angle, which acts as a pseudo magnetic field. The phason provided by the sliding of the layers lives on 2n-tori and can be used to access and manipulate the edge states. Our work demonstrates how multi-layered systems are virtual laboratories for studying the physics of higher dimensional quantum Hall effect, and can be employed to engineer topological pumps via simple twisting and sliding.

scholarly journals Half-Dirac Semimetal and Quantum Anomalous Hall Effect in Kagome Cd2N3 Lattice

2020 ◽  
Author(s):  
Xinyang Li ◽  
Weixiao Ji ◽  
Peiji Wang ◽  
Chang-wen Zhang
Keyword(s):  
Hall Effect ◽  
Quantum State ◽  
Anomalous Hall Effect ◽  
Topological Phases ◽  
Dirac Semimetal ◽  
Quantum Anomalous Hall Effect ◽  
Dirac Materials ◽  
Low Dimensionality ◽  
Dirac Semimetals ◽  
Topological Phases Of Matter

Half-Dirac semimetals (HDSs), which possess 100% spin-polarizations for Dirac materials, are highly desirable for exploring various topological phases of matter, as low-dimensionality opens unprecedented opportunities for manipulating the quantum state...

Topological Phases of Matter

2021 ◽  
Author(s):  
Roderich Moessner ◽  
Joel E. Moore
Keyword(s):  
Topological Phases ◽  
Topological Phases Of Matter

scholarly journals Electrically tunable low-density superconductivity in a monolayer topological insulator

Science ◽  
2018 ◽  
Vol 362 (6417) ◽  
pp. 926-929 ◽  
Author(s):  
Valla Fatemi ◽  
Sanfeng Wu ◽  
Yuan Cao ◽  
Landry Bretheau ◽  
Quinn D. Gibson ◽  
...  
Keyword(s):  
Ground State ◽  
Field Effect ◽  
Field Effect Transistor ◽  
Quantum Spin ◽  
Topological Phases ◽  
Critical Temperatures ◽  
Topological States ◽  
Effect Transistor ◽  
Topological Phases Of Matter

Turning on superconductivity in a topologically nontrivial insulator may provide a route to search for non-Abelian topological states. However, existing demonstrations of superconductor-insulator switches have involved only topologically trivial systems. Here we report reversible, in situ electrostatic on-off switching of superconductivity in the recently established quantum spin Hall insulator monolayer tungsten ditelluride (WTe2). Fabricated into a van der Waals field-effect transistor, the monolayer’s ground state can be continuously gate-tuned from the topological insulating to the superconducting state, with critical temperaturesTcup to ~1 kelvin. Our results establish monolayer WTe2as a material platform for engineering nanodevices that combine superconducting and topological phases of matter.

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