Experimental evidence and control of the bulk-mediated intersurface coupling in topological insulator Bi2Te2Se nanoribbons

TL;DR

This study provides experimental evidence and control methods for bulk-mediated intersurface coupling in Bi2Te2Se nanoribbons, advancing understanding of topological surface states and their interactions with bulk carriers.

Contribution

It demonstrates the first direct evidence and control of bulk-surface coupling in topological insulator nanoribbons through magnetoresistance measurements.

Findings

Coherent channels change with film thickness exceeding bulk phase relaxation length

Bulk-mediated coupling occurs between states on opposite surfaces

Gate voltages and magnetic fields can modulate intersurface coupling

Abstract

Nearly a decade after the discovery of topological insulators (TIs), the important task of identifying and characterizing their topological surface states through electrical transport experiments remains incomplete. The interpretation of these experiments is made difficult by the presence of residual bulk carriers and their coupling to surface states, which is not yet well understood. In this work, we present the first evidence for the existence and control of bulk-surface coupling in Bi2Te2Se nanoribbons, which are promising platforms for future TI-based devices. Our magnetoresistance measurements reveal that the number of coherent channels contributing to quantum interference in the nanoribbons changes abruptly when the film thickness exceeds the bulk phase relaxation length. We interpret this observation as an evidence for bulk-mediated coupling between metallic states located on opposite surfaces. This hypothesis is supported by additional magnetoresistance measurements conducted under a set of gate voltages and in a parallel magnetic field, the latter of which alters the intersurface coupling in a controllable way.