Nanomechanical characterization of quantum interference in a topological insulator nanowire

TL;DR

This paper demonstrates nanomechanical measurements revealing Aharonov-Bohm oscillations in the density of states of a topological insulator nanowire, providing a new way to observe quantum interference effects in topological materials.

Contribution

It introduces a novel nanomechanical approach to detect quantum capacitance effects and observe AB oscillations in the DOS of topological insulator nanowires, which had not been previously observed.

Findings

Detection of AB oscillations in DOS via nanomechanical resonator.

Quantum capacitance modulates resonant frequency shifts.

Technique applicable to diverse quantum materials.

Abstract

The discovery of two-dimensional gapless Dirac fermions in graphene and topological insulators (TI) has sparked extensive ongoing research toward applications of their unique electronic properties. The gapless surface states in three-dimensional insulators indicate a distinct topological phase of matter with a non-trivial Z2 invariant that can be verified by angle-resolved photoemission spectroscopy or magnetoresistance quantum oscillation. In TI nanowires, the gapless surface states exhibit Aharonov-Bohm (AB) oscillations in conductance, with this quantum interference effect accompanying a change in the number of transverse one-dimensional modes in transport. Thus, while the density of states (DOS) of such nanowires is expected to show such AB oscillation, this effect has yet to be observed. Here, we adopt nanomechanical measurements that reveal AB oscillations in the DOS of a topological insulator. The TI nanowire under study is an electromechanical resonator embedded in an electrical circuit, and quantum capacitance effects from DOS oscillation modulate the circuit capacitance thereby altering the spring constant to generate mechanical resonant frequency shifts. Detection of the quantum capacitance effects from surface-state DOS is facilitated by the small effective capacitances and high quality factors of nanomechanical resonators, and as such the present technique could be extended to study diverse quantum materials at nanoscale.