Topological delocalization and tuning of surface channel separation in Bi2Se2Te Topological Insulator Thin films

TL;DR

This paper demonstrates how tuning the chemical potential in Bi2Se2Te topological insulator thin films can suppress bulk conduction, enhance surface state transport, and control surface coupling, advancing understanding of topological protection.

Contribution

It introduces a method to tune the chemical potential in Bi2Se2Te thin films, suppress bulk carriers, and decouple surface states, improving topological surface transport.

Findings

Bulk carriers can be suppressed by chemical potential tuning.

Surface states exhibit robustness evidenced by 2D weak antilocalization.

Decoupling of surface states reduces bulk transport contribution.

Abstract

The surface states of a 3D topological insulator (TI) exhibit topological protection against backscattering. However, the contribution of bulk electrons to the transport data is an impediment to the topological protection of surface. We report the tuning of the chemical potential in the bulk of Bi2Se2Te TI thin films, pinning it near the center of the bulk band gap, thereby suppressing the bulk carriers. The temperature dependent resistance of these films shows activated behavior down to 50K, followed by a metallic transition at lower temperatures, a hallmark of the robustness of TI surface states. Manifestation of topological protection and surface dominated transport is explained by 2D weak antilocalization phenomenon. We further explore the effect of surface to bulk coupling in TI in this work, which is captured by the number of effective conducting surface channels that participate in the transport. The presence of a single conducting channel indicates a strong surface to bulk coupling which is detrimental to purely topological transport. We demonstrate the decoupling of topological surface states on opposite surfaces of thin films, thereby suppressing the bulk transport. Our findings provide a deeper understanding of surface to bulk coupling along with topological transport behavior and their respective tunability.