RF compressibility of topological surface and interface states in metal-hBN-Bi2Se3 capacitors

TL;DR

This paper uses RF admittance measurements to analyze the compressibility and velocity of topological surface states in Bi2Se3-based capacitors, revealing insights into Dirac fermions and trivial states.

Contribution

It introduces RF quantum capacitance techniques to probe topological surface states and distinguishes between topological and trivial surface contributions.

Findings

Measured Dirac state compressibility via RF admittance.

Demonstrated ambipolar effect in quantum capacitance.

Determined surface Dirac fermion velocities in different device configurations.

Abstract

The topological state that emerges at the surface of a topological insulator (TI) and at the TI-substrate interface are studied in metal-hBN-Bi2Se3 capacitors. By measuring the RF admittance of the capacitors versus gate voltage, we extract the compressibility of the Dirac state located at a gated TI surface. We show that even in the presence of an ungated surface that hosts a trivial electron accumulation layer, the other gated surface always exhibits an ambipolar effect in the quantum capacitance. We succeed in determining the velocity of surface Dirac fermions in two devices, one with a passivated surface and the other with a free surface that hosts trivial states. Our results demonstrate the potential of RF quantum capacitance techniques to probe surface states of systems in the presence of a parasitic density-of-states.