Independence of topological surface state and bulk conductances in three-dimensional topological insulators

TL;DR

This study demonstrates that in certain three-dimensional topological insulators, the surface state conductance remains unaffected by changes in bulk conductance at low temperatures, confirming their decoupled nature and suitability for 2D Dirac electron research.

Contribution

First experimental comparison showing decoupling of surface and bulk conductances in specific topological insulators using temperature-dependent high-pressure measurements.

Findings

Surface conductance remains constant despite increased bulk conductance.

Surface and bulk states are decoupled at low temperatures.

Supports theoretical models of topological insulators.

Abstract

The archetypical 3D topological insulators Bi2Se3, Bi2Te3 and Sb2Te3 commonly exhibit high bulk conductivities, hindering the characterization of the surface state charge transport. The optimally doped topological insulators Bi2Te2Se and Bi2-xSbxTe2S, however, allow for such characterizations to be made. Here we report the first experimental comparison of the topological surface states and bulk conductances of Bi2Te2Se and Bi1.1Sb0.9Te2S, based on temperature-dependent high-pressure measurements. We find that the surface state conductance at low temperatures remains constant in the face of orders of magnitude increase in the bulk state conductance, revealing in a straightforward way that the topological surface states and bulk states are decoupled at low temperatures, consistent with theoretical models, and confirming topological insulators to be an excellent venue for studying charge transport in 2D Dirac electron systems.