Coherent Topological Transport on the Surface of Bi2Se3

TL;DR

This paper investigates the coherence and coupling of topological surface states in Bi2Se3 thin films, revealing that even at 12 nm thickness, surfaces can remain coherently coupled, affecting their topological transport properties.

Contribution

It demonstrates that weak anti-localization is highly sensitive to inter-surface coupling, showing that top and bottom surfaces can remain coherently coupled at larger thicknesses than previously thought.

Findings

Weak anti-localization detects inter-surface coupling.

Surfaces can be coherently coupled up to 12 nm thickness.

Thicker films exhibit signatures of decoupled topological surfaces.

Abstract

The two-dimensional (2D) surface state of the three-dimensional strong topological insulator (STI) is fundamentally distinct from other 2D electron systems in that the Fermi arc encircles an odd number of Dirac points. The TI surface is in the symplectic universality class and uniquely among 2D systems remains metallic and cannot be localized by (time-reversal symmetric) disorder. However, in finite-size samples inter-surface coupling can destroy the topological protection. The question arises: At what size can a thin TI sample be treated as having decoupled topological surface states? We show that weak anti-localization(WAL) is extraordinarily sensitive to sub-meV coupling between top and bottom topological surfaces, and the surfaces of a TI film may be coherently coupled even for thicknesses as large as 12 nm. For thicker films we observe the signature of a true 2D topological metal: perfect weak anti-localization in quantitative agreement with two decoupled surfaces in the symplectic symmetry class.