Observation of Anderson localization in ultrathin films of three-dimensional topological insulators

TL;DR

This paper experimentally demonstrates the transition from diffusive to localized transport in ultrathin topological insulator films, revealing the critical role of disorder in their quantum transport properties and topological phase transitions.

Contribution

First direct observation of Anderson localization transition in ultrathin topological insulator films, linking disorder effects to topological phase physics.

Findings

Transition from weak antilocalization to variable range hopping transport.

Suppression of negative magnetoconductivity with increasing disorder.

Emergence of positive magnetoconductivity in the localized regime.

Abstract

Anderson localization, the absence of diffusive transport in disordered systems, has been manifested as hopping transport in numerous electronic systems, whereas in recently discovered topological insulators it has not been directly observed. Here we report experimental demonstration of transition from diffusive transport in the weak antilocalization regime to variable range hopping transport in the Anderson localization regime with ultrathin (Bi$_{1-x}$Sb$_x$)$_2$Te$_3$ films. As disorder becomes stronger, negative magnetoconductivity due to the weak antilocalization is gradually suppressed, and eventually positive magnetoconductivity emerges when the electron system becomes strongly localized. This works reveals the critical role of disorder in the quantum transport properties of ultrathin topological insulator films, in which theories have predicted rich physics related to topological phase transitions.