Mapping propagation of collective modes in Bi2Se3 and Bi2Te2.2Se0.8 topological insulators by near-field terahertz nanoscopy

AbstractNear-field microscopy discloses a peculiar potential to explore novel quantum state of matter at the nanoscale, providing an intriguing playground to investigate, locally, carrier dynamics or propagation of photoexcited modes as plasmons, phonons, plasmon-polaritons or phonon-polaritons. Here, we exploit a combination of hyperspectral time domain spectroscopy nano-imaging and detectorless scattering near-field optical microscopy, at multiple terahertz frequencies, to explore the rich physics of layered topological insulators as Bi2Se3 and Bi2Te2.2Se0.8, hyperbolic materials with topologically protected surface states. By mapping the near-field scattering signal from a set of thin flakes of Bi2Se3 and Bi2Te2.2Se0.8 of various thicknesses, we shed light on the nature of the collective modes dominating their optical response in the 2-3 THz range. We capture snapshots of the activation of transverse and longitudinal optical phonons and reveal the propagation of sub-diffractional hyperbolic phonon-polariton modes influenced by the Dirac plasmons arising from the topological surface states and of bulk plasmons, prospecting new research directions in plasmonics, tailored nanophotonics, spintronics and quantum technologies.

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Discovery of a weak topological insulating state and van Hove singularity in triclinic RhBi2

Nature Communications ◽

10.1038/s41467-021-22136-w ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Kyungchan Lee ◽

Gunnar F. Lange ◽

Lin-Lin Wang ◽

Brinda Kuthanazhi ◽

Thaís V. Trevisan ◽

...

Keyword(s):

Time Reversal ◽

Topological Insulators ◽

Dirac Point ◽

Saddle Points ◽

Surface States ◽

Van Hove Singularity ◽

Space Group ◽

Topological Materials ◽

Topological Surface ◽

Optimal Space

AbstractTime reversal symmetric (TRS) invariant topological insulators (TIs) fullfil a paradigmatic role in the field of topological materials, standing at the origin of its development. Apart from TRS protected strong TIs, it was realized early on that more confounding weak topological insulators (WTI) exist. WTIs depend on translational symmetry and exhibit topological surface states only in certain directions making it significantly more difficult to match the experimental success of strong TIs. We here report on the discovery of a WTI state in RhBi2 that belongs to the optimal space group P$$\bar{1}$$ 1 ¯ , which is the only space group where symmetry indicated eigenvalues enumerate all possible invariants due to absence of additional constraining crystalline symmetries. Our ARPES, DFT calculations, and effective model reveal topological surface states with saddle points that are located in the vicinity of a Dirac point resulting in a van Hove singularity (VHS) along the (100) direction close to the Fermi energy (EF). Due to the combination of exotic features, this material offers great potential as a material platform for novel quantum effects.

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Current-Induced Spin Torque on Magnetization Textures Coupled to the Topological Surface States of Three-Dimensional Topological Insulators

Journal of the Physical Society of Japan ◽

10.7566/jpsj.83.064710 ◽

2014 ◽

Vol 83 (6) ◽

pp. 064710 ◽

Cited By ~ 9

Author(s):

Ji Chen ◽

Mansoor Bin Abdul Jalil ◽

Seng Ghee Tan

Keyword(s):

Topological Insulators ◽

Three Dimensional ◽

Surface States ◽

Spin Torque ◽

Topological Surface

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Persistent coherence and spin polarization of topological surface states on topological insulators

Physical Review B ◽

10.1103/physrevb.88.041101 ◽

2013 ◽

Vol 88 (4) ◽

Cited By ~ 15

Author(s):

Z.-H. Pan ◽

E. Vescovo ◽

A. V. Fedorov ◽

G. D. Gu ◽

T. Valla

Keyword(s):

Spin Polarization ◽

Topological Insulators ◽

Surface States ◽

Topological Surface

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Giant photoinduced anomalous Hall effect of the topological surface states in three dimensional topological insulators Bi2Te3

Applied Physics Letters ◽

10.1063/1.5145359 ◽

2020 ◽

Vol 116 (14) ◽

pp. 141603

Author(s):

Jinling Yu ◽

Wenyi Wu ◽

Yumeng Wang ◽

Kejing Zhu ◽

Xiaolin Zeng ◽

...

Keyword(s):

Hall Effect ◽

Topological Insulators ◽

Three Dimensional ◽

Surface States ◽

Anomalous Hall Effect ◽

Topological Surface

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Spintronics Based on Topological Insulators

SPIN ◽

10.1142/s2010324716400014 ◽

2016 ◽

Vol 06 (02) ◽

pp. 1640001 ◽

Cited By ~ 38

Author(s):

Yabin Fan ◽

Kang L. Wang

Keyword(s):

Topological Insulators ◽

Spin Injection ◽

Surface States ◽

Research Field ◽

Spin Torque ◽

Spin Orbit ◽

Challenges And Opportunities ◽

Potential Applications ◽

Topological Surface ◽

A Charge

Spintronics using topological insulators (TIs) as strong spin–orbit coupling (SOC) materials have emerged and shown rapid progress in the past few years. Different from traditional heavy metals, TIs exhibit very strong SOC and nontrivial topological surface states that originate in the bulk band topology order, which can provide very efficient means to manipulate adjacent magnetic materials when passing a charge current through them. In this paper, we review the recent progress in the TI-based magnetic spintronics research field. In particular, we focus on the spin–orbit torque (SOT)-induced magnetization switching in the magnetic TI structures, spin–torque ferromagnetic resonance (ST-FMR) measurements in the TI/ferromagnet structures, spin pumping and spin injection effects in the TI/magnet structures, as well as the electrical detection of the surface spin-polarized current in TIs. Finally, we discuss the challenges and opportunities in the TI-based spintronics field and its potential applications in ultralow power dissipation spintronic memory and logic devices.

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A Chemical Theory of Topological Insulators

10.26434/chemrxiv.7637009 ◽

2019 ◽

Author(s):

Angel Martín Pendás ◽

Julia Contreras-García ◽

Fernanda Pinilla ◽

José Daniel Mella ◽

Carlos Cárdenas ◽

...

Keyword(s):

Topological Insulators ◽

Surface States ◽

Chemical Theory ◽

Protected Surface ◽

Symmetry Protected ◽

Chemical Description

This article presents a chemical description of a simple topological insulators model in order to translate concepts such as "symmetry protected", "surface states" to the chemistry vocabulary

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Magnetizing topological surface states of Bi2Se3 with a CrI3 monolayer

Science Advances ◽

10.1126/sciadv.aaw1874 ◽

2019 ◽

Vol 5 (5) ◽

pp. eaaw1874 ◽

Cited By ~ 19

Author(s):

Yusheng Hou ◽

Jeongwoo Kim ◽

Ruqian Wu

Keyword(s):

Density Functional ◽

Topological Insulators ◽

Dirac Point ◽

Surface States ◽

Anomalous Hall Effect ◽

Spin Splitting ◽

Topological Feature ◽

Topological Parameters ◽

General Rules ◽

Topological Surface

To magnetize surfaces of topological insulators without damaging their topological feature is a crucial step for the realization of the quantum anomalous Hall effect (QAHE) and remains as a challenging task. Through density functional calculations, we found that adsorption of a semiconducting two-dimensional van der Waals (2D-vdW) ferromagnetic CrI3 monolayer can create a sizable spin splitting at the Dirac point of the topological surface states of Bi2Se3 films. Furthermore, general rules that connect different quantum and topological parameters are established through model analyses. This work provides a useful guideline for the realization of QAHE at high temperatures in heterostructures of 2D-vdW magnetic monolayers and topological insulators.

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Electron–hole asymmetry of the topological surface states in strained HgTe

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1611663114 ◽

2017 ◽

Vol 114 (13) ◽

pp. 3381-3386 ◽

Cited By ~ 5

Author(s):

Andreas Jost ◽

Michel Bendias ◽

Jan Böttcher ◽

Ewelina Hankiewicz ◽

Christoph Brüne ◽

...

Keyword(s):

Topological Insulators ◽

Quantum Hall ◽

Surface States ◽

Metallic Surface ◽

Electron Hole ◽

Linear Dispersion ◽

Strong Electron ◽

Quantum Oscillations ◽

Strong Deviation ◽

Topological Surface

Topological insulators are a new class of materials with an insulating bulk and topologically protected metallic surface states. Although it is widely assumed that these surface states display a Dirac-type dispersion that is symmetric above and below the Dirac point, this exact equivalence across the Fermi level has yet to be established experimentally. Here, we present a detailed transport study of the 3D topological insulator-strained HgTe that strongly challenges this prevailing viewpoint. First, we establish the existence of exclusively surface-dominated transport via the observation of an ambipolar surface quantum Hall effect and quantum oscillations in the Seebeck and Nernst effect. Second, we show that, whereas the thermopower is diffusion driven for surface electrons, both diffusion and phonon drag contributions are essential for the hole surface carriers. This distinct behavior in the thermoelectric response is explained by a strong deviation from the linear dispersion relation for the surface states, with a much flatter dispersion for holes compared with electrons. These findings show that the metallic surface states in topological insulators can exhibit both strong electron–hole asymmetry and a strong deviation from a linear dispersion but remain topologically protected.

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