Tunable quantum spin Hall effect in double quantum wells

TL;DR

This paper demonstrates that a double quantum well system can exhibit a tunable quantum spin Hall effect driven by inter-layer bias, enabling controllable topological phases in materials without valley degeneracy.

Contribution

It introduces a method to induce and control topological insulator phases in HgTe-based double quantum wells via bias voltage, expanding the possibilities for topological device applications.

Findings

TI phase can be driven by inter-layer bias in double QWs

Double QWs exhibit layer-pseudospin physics similar to bilayer graphene

System allows control of topological phases without valley degeneracy

Abstract

The field of topological insulators (TIs) is rapidly growing. Concerning possible applications, the search for materials with an easily controllable TI phase is a key issue. The quantum spin Hall effect, characterized by a single pair of helical edge modes protected by time-reversal symmetry, has been demonstrated in HgTe-based quantum wells (QWs) with an inverted bandgap. We analyze the topological properties of a generically coupled HgTe-based double QW (DQW) and show how in such a system a TI phase can be driven by an inter-layer bias voltage, even when the individual layers are non-inverted. We argue, that this system allows for similar (layer-)pseudospin based physics as in bilayer graphene but with the crucial absence of a valley degeneracy.