Weak localization of bulk channels in topological insulator thin film

TL;DR

This paper investigates the origin of weak antilocalization in topological insulators, revealing that bulk states can exhibit weak localization effects that influence overall magnetoconductivity, challenging the assumption that WAL solely arises from surface states.

Contribution

It introduces a modified massive Dirac model for 2D bulk subbands in topological insulator thin films and derives magnetoconductivity formulas accounting for bulk contributions, highlighting their potential to cause weak localization.

Findings

Bulk 2D subbands can show weak localization instead of WAL.

Bulk states may reduce or reverse surface WAL effects.

Magnetoconductivity inflections indicate bulk WL dominance.

Abstract

Weak antilocalization (WAL) is expected whenever strong spin-orbit coupling or scattering comes into play. Spin-orbit coupling in the bulk states of a topological insulator is very strong, enough to result in the topological phase transition. However, the recently observed WAL in topological insulators seems to have an ambiguous origin from the bulk states. Starting from the effective model for three-dimensional topological insulators, we find that the lowest two-dimensional (2D) bulk subbands of a topological insulator thin film can be described by the modified massive Dirac model. We derive the magnetoconductivity formula for both the 2D bulk subbands and surface bands. Because with Relatively large gap, the 2D bulk subbands may lie in the regimes where the unitary behavior or even weak localization (WL) is also expected, instead of always WAL. As a result, the bulk states may contribute small magnetoconductivity or even compensate the WAL from the surface states. Inflection in magnetoconductivity curves may appear when the bulk WL channels outnumber the surface WAL channels, providing a signature of the weak localization from the bulk states.