Electric control of inverted gap and hybridization gap in type-II InAs/GaSb quantum wells

The quantum spin Hall effect has been predicted theoretically and observed experimentally in InAs/GaSb quantum wells as a result of inverted band structures, for which electron bands in InAs layers are below heavy-hole bands in GaSb layers in energy. The hybridization between electron bands and heavy-hole bands leads to a hybridization gap away from k=0. A recent puzzling observation in experiments is that when the system is tuned to more inverted regime by a gate voltage (a larger inverted gap at k=0), the hybridization gap decreases. Motivated by this experiment, we explore the dependence of the hybridization gap as a function of external electric fields based on the eight-band Kane model. We identify two regimes when varying the electric fields: (1) Both inverted and hybridization gaps increase and (2) the inverted gap increases while the hybridization gap decreases. Based on the effective model, we find that light-hole bands in GaSb layers play an important role in determining the hybridization gap. In addition, a large external electric field can induce a strong Rashba splitting and also influence the hybridization gap.