Asymmetric versus symmetric HgTe / Cd x Hg 1 - X Te double quantum wells: Bandgap tuning without electric field

Abstract

We investigate the electron states in double asymmetric HgTe / Cd x Hg 1 - x Te quantum wells grown along the [001] direction. The subbands are computed by means of the envelope function approximation applied to the eight-band Kane k ⋅ p model. The asymmetry of the confining potential of the double quantum wells results in a gap opening, which is absent in the symmetric system where it can only be induced by an applied electric field. The bandgap and the subbands are affected by spin-orbit coupling, which is a consequence of the asymmetry of the confining potential. The electron-like and hole-like states are mainly confined in different quantum wells, and the enhanced hybridization between them opens a spin-dependent hybridization gap at a finite in-plane wavevector. We show that both the ratio of the widths of the two quantum wells and the mole fraction of the C d x H g 1 - x Te barrier control both the energy gap between the hole-like states and the hybridization gap. The energy subbands are shown to exhibit inverted ordering, and therefore, a nontrivial topological phase could emerge in the system. © 2020 Author(s).