Quantum Spin Hall Effect in Inverted Type II Semiconductors

TL;DR

This paper predicts the existence of a quantum spin Hall state in InAs/GaSb/AlSb quantum wells, demonstrating a topologically non-trivial phase with potential for electrical control, similar to HgTe quantum wells.

Contribution

The work introduces a new material system (InAs/GaSb/AlSb quantum wells) exhibiting a quantum spin Hall state with tunable phase transition, expanding the class of topological insulators.

Findings

QSH state predicted in InAs/GaSb/AlSb quantum wells

Quantum phase transition tunable by gate voltage

Persistence of QSH state with symmetry-breaking effects

Abstract

The quantum spin Hall (QSH) state is a topologically non-trivial state of quantum matter which preserves time-reversal symmetry; it has an energy gap in the bulk, but topologically robust gapless states at the edge. Recently, this novel effect has been predicted and observed in HgTe quantum wells. In this work we predict a similar effect arising in Type-II semiconductor quantum wells made from InAs/GaSb/AlSb. Because of a rare band alignment the quantum well band structure exhibits an "inverted" phase similar to CdTe/HgTe quantum wells, which is a QSH state when the Fermi level lies inside the gap. Due to the asymmetric structure of this quantum well, the effects of inversion symmetry breaking and inter-layer charge transfer are essential. By standard self-consistent calculations, we show that the QSH state persists when these corrections are included, and a quantum phase transition between the normal insulator and the QSH phase can be electrically tuned by the gate voltage.