Freestanding few-layer sheets of a dual topological insulator

Mai Lê Anh,Pavel Potapov,Axel Lubk,Michael Ruck,Thomas Doert

doi:10.1038/s41699-021-00203-6

Abstract

The emergence of topological insulators (TIs) raised high expectations for their application in quantum computers and spintronics. Being bulk semiconductors, their nontrivial topology at the electronic bandgap enables dissipation-free charge and spin transport in protected metallic surface states. For application, crystalline thin films are requested in sufficient quantity. A suitable approach is the liquid phase exfoliation (LPE) of TI crystals that have layered structures. Bi2TeI is a weak 3D TI, which leads to protected edge states at the side facets of a crystal, as well as a topological crystalline insulator, which is responsible for protected states at the top and bottom faces. We developed an effective, scalable protocol for LPE of freestanding nanoflakes from Bi2TeI crystals. By heat treatment and sonication in isopropyl alcohol and poly(vinylpyrrolidone), crystalline Bi2TeI sheets with a thickness of ~50 nm were obtained and can therefore be considered for further processing toward microelectronic applications.

Highlights

Topological insulators (TIs) are a relatively new class of quantum materials, which are currently heavily investigated for their intriguing fundamental properties, as well as possible applications in future electronic and spintronic devices
Thereby, it is anticipated that the solvent induces swelling by an inclusion of suitable solvent molecules in the interlayer spaces
Common solvents that are used for liquid phase exfoliation (LPE) are, for example, N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), and isopropyl alcohol (IPA)[16]

Summary

Introduction

Topological insulators (TIs) are a relatively new class of quantum materials, which are currently heavily investigated for their intriguing fundamental properties, as well as possible applications in future electronic and spintronic devices. Mobile electrons that are protected against backscattering by timeinversion symmetry and topology exist on the surface of TIs1–3 Their spin is locked orthogonal to their propagation direction, i.e., attaching a spin current to electrons traveling into a particular direction. These two properties make TIs highly desirable materials for quantum computing and spintronics[4,5] by virtue of the topology and symmetry of their band structure[1,6]. According to the Z2 classification and dimensionality, TIs may be classified in to 2D TIs (a quantum spin Hall state) and 3D strong and weak TIs (WTI) The latter exhibit topologically nontrivial surface states only at particular surfaces (indicated by the invariants) and may be obtained from stacking 2D TIs along the out-of-plane direction. Applications in micro- or nanoelectronics require thin TI films of high quality, as well as a reasonable processing and scalability

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Results

Conclusion