New interpretation of the origin of 2DEG states at the surface of layered topological insulators

TL;DR

This paper reveals that the formation of 2DEG states at layered topological insulator surfaces is driven by van der Waals spacing expansion due to intercalation, affecting surface state localization and scattering.

Contribution

It provides a new interpretation linking 2DEG emergence to vdW expansion caused by intercalation, supported by relativistic ab-initio calculations.

Findings

2DEG states arise from vdW expansion caused by intercalation.

Relocation of topological surface states explains experimental scattering results.

Expansion of vdW spacings induces Rashba-splitting in 2DEG bands.

Abstract

On the basis of relativistic ab-initio calculations we show that the driving mechanism of simultaneous emergence of parabolic and M-shaped 2D electron gas (2DEG) bands at the surface of layered topological insulators as well as Rashba-splitting of the former states is an expansion of van der Waals (vdW) spacings caused by intercalation of metal atoms or residual gases. The expansion of vdW spacings and emergence of the 2DEG states localized in the (sub)surface region are also accompanied by a relocation of the topological surface state to the lower quintuple layers, that can explain the absence of interband scattering found experimentally.