Landau Levels of Topologically-Protected Surface States Probed by Dual-Gated Quantum Capacitance

TL;DR

This study measures Landau levels of topologically protected surface states in 3D topological insulators using dual-gated quantum capacitance, providing quantitative insights into their electronic structure and quantum Hall states.

Contribution

It introduces a method to directly measure Landau level energies of surface states in bulk-insulating 3D TIs using quantum capacitance in a dual-gated heterostructure.

Findings

Quantitative Landau level energies for topological surface states obtained.

Identification of Landau levels at different quantum Hall states.

Demonstration of dual-gate control over surface state electronic properties.

Abstract

Spectroscopy of discrete Landau levels (LLs) in bulk-insulating three-dimensional topological insulators (3D TIs) in perpendicular magnetic field characterizes the Dirac nature of their surface states. Despite a number of studies demonstrating the quantum Hall effect (QHE) of topological surface states, quantitative evaluation of the LL energies, which serve as fundamental electronic quantities for study of the quantum states, is still limited. In this work, we explore the density of states of LLs by measuring quantum capacitance (CQ) in a truly bulk insulating 3D TI via a van der Waals heterostructure configuration. By applying dual gate voltages, we access the individual surface states' LLs and extract their chemical potentials to quantify the LL spacings of each surface. We evaluate the LLs' energies at two distinguished QH states, namely dissipationless ({\nu}= +/-1) and dissipative ({\nu}= 0) states in the 3D TI.