Tunable Coupling between Surface States of a Three-Dimensional Topological Insulator in the Quantum Hall Regime

TL;DR

This study demonstrates tunable capacitive coupling between surface states of a 3D topological insulator, revealing non-linear quantum Hall transitions and inter-surface hybridization, advancing understanding of topological quantum effects.

Contribution

It introduces a method to control and analyze the coupling of surface states in a 3D topological insulator using dual-gate techniques, revealing new quantum Hall phenomena.

Findings

Observation of non-linear quantum Hall transitions at low charge density

Splitting of the N=0 Landau level indicating inter-surface hybridization

Extraction of Landau level energy gaps from dual-gated measurements

Abstract

The paired top and bottom Dirac surface states, each associated with a half-integer quantum Hall (QH) effect, and a resultant integer QH conductance ({\nu}e2/h), are hallmarks of a three-dimensional (3D) topological insulator (TI). In a dual-gated system, chemical potentials of the paired surface states are controlled through separate gates. In this work, we establish tunable capacitive coupling between the surface states of a bulk-insulating TI BiSbTeSe2 and study the effect of this coupling on QH plateaus and Landau level (LL) fan diagram via dual-gate control. We observe non-linear QH transitions at low charge density in strongly-coupled surface states, which are related to the charge-density-dependent coupling strength. A splitting of the N= 0 LL at the charge neutrality point for thin devices (but thicker than the 2D limit) indicates inter-surface hybridization possibly beyond single-particle effects. By applying capacitor charging models to the surface states, we explore their chemical potential as a function of charge density and extract the fundamental electronic quantity of LL energy gaps from dual-gated transport and capacitance measurements. These studies are essential for the realization of exotic quantum effects such as topological exciton condensation.