Quantum Spin Hall Effect in Inverted Type-II Semiconductors

TLDR

The quantum spin Hall state is a topologically nontrivial phase with a bulk energy gap and protected edge states, and inverted quantum wells such as HgTe/CdTe exhibit this behavior when the Fermi level lies within the gap. This work predicts that InAs/GaSb/AlSb type‑II quantum wells will also host a quantum spin Hall state. The asymmetric structure of the InAs/GaSb/AlSb quantum well makes inversion‑symmetry breaking essential for realizing the topological phase. The transition between the trivial insulator and the quantum spin Hall state can be continuously tuned by gate voltage, allowing quantitative study of the phase transition.

Abstract

The quantum spin Hall (QSH) state is a topologically nontrivial 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 and in this Letter we predict a similar effect arising in Type-II semiconductor quantum wells made from $\mathrm{InAs}/\mathrm{GaSb}/\mathrm{AlSb}$. The quantum well exhibits an ``inverted'' phase similar to $\mathrm{HgTe}/\mathrm{CdTe}$ 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 are essential. Remarkably, the topological quantum phase transition between the conventional insulating state and the quantum spin Hall state can be continuously tuned by the gate voltage, enabling quantitative investigation of this novel phase transition.