Topological Insulator-Based van der Waals Heterostructures for Effective Control of Massless and Massive Dirac Fermions

TL;DR

This paper demonstrates the use of van der Waals heterostructures with magnetic and non-magnetic insulators to precisely control the electronic properties of topological insulator surface states, enabling tuning of massless and massive Dirac fermions.

Contribution

It introduces a vdW heterostructure platform with magnetic and non-magnetic insulators to tune the chemical potential and gap of topological surface states in TIs.

Findings

Improved quantization of TSS with hBN/graphite gating.

Observation of half-quantized Hall conductance steps with CGT/graphite gating.

Effective control of Dirac fermions in TI heterostructures.

Abstract

Three dimensional (3D) topological insulators (TIs) are an important class of materials with applications in electronics, spintronics and quantum computing. With the recent development of truly bulk insulating 3D TIs, it has become possible to realize surface dominated phenomena in electrical transport measurements e.g. the quantum Hall (QH) effect of massless Dirac fermions in topological surface states (TSS). However, to realize more advanced devices and phenomena, there is a need for a platform to tune the TSS or modify them e.g. gap them by proximity with magnetic insulators, in a clean manner. Here we introduce van der Waals (vdW) heterostructures in the form of topological insulator/insulator/graphite to effectively control chemical potential of the TSS. Two types of gate dielectrics, normal insulator hexagonal boron nitride (hBN) and ferromagnetic insulator Cr2Ge2Te6 (CGT) are utilized to tune charge density of TSS in the quaternary TI BiSbTeSe2. hBN/graphite gating in the QH regime shows improved quantization of TSS by suppression of magnetoconductivity of massless Dirac fermions. CGT/graphite gating of massive Dirac fermions in the QH regime yields half-quantized Hall conductance steps and a measure of the Dirac gap. Our work shows the promise of the vdW platform in creating advanced high-quality TI-based devices.