Coexistence of bulk and surface states probed by Shubnikov-de Haas oscillations in Bi$_2$Se$_3$ with high charge-carrier density

TL;DR

This study investigates the coexistence of bulk and surface conduction channels in Bi$_2$Se$_3$ topological insulator thin films using high-field Shubnikov-de Haas oscillations, revealing complex parallel conduction mechanisms.

Contribution

It provides experimental evidence of bulk and surface state coexistence and highlights the need for theoretical models to understand their interplay in topological insulators.

Findings

Identification of Zeeman-split bulk conduction contribution

Detection of a two-dimensional surface state

Evidence of additional conduction channels with unclear origin

Abstract

Topological insulators are ideally represented as having an insulating bulk with topologically protected, spin-textured surface states. However, it is increasingly becoming clear that these surface transport channels can be accompanied by a finite conducting bulk, as well as additional topologically trivial surface states. To investigate these parallel conduction transport channels, we studied Shubnikov-de Haas oscillations in Bi$_2$Se$_3$ thin films, in high magnetic fields up to 30 T so as to access channels with a lower mobility. We identify a clear Zeeman-split bulk contribution to the oscillations from a comparison between the charge-carrier densities extracted from the magnetoresistance and the oscillations. Furthermore, our analyses indicate the presence of a two-dimensional state and signatures of additional states the origin of which cannot be conclusively determined. Our findings underpin the necessity of theoretical studies on the origin of and the interplay between these parallel conduction channels for a careful analysis of the material's performance.