Spin polarization of an electron-hole gas in InAs/GaSb quantum wells under a dc current

We have investigated the spin polarization of electrons and holes in InAs/GaSb broken-gap quantum wells under nonequilibrium conditions when a dc electric field is applied parallel to interfaces. The existence of a nonzero asymmetric part of the quasiparticle distribution function caused by the dc current and the spin-split of the electron-hole hybridized states generates a finite spin polarization in both the InAs layer and the GaSb layer. With a very weak asymmetry of the distribution function, our self-consistent calculation yields about 1% spin polarization for electrons in the InAs layer and holes in the GaSb layer. The signs of these spin polarizations depend on the widths of the layers, changing the widths drives a phase transition in the electron-hole gas between the hybridized semiconducting phase and the normal semiconducting phase. In the hybridized semiconducting phase, the spin polarizations in both the InAs layer and the GaSb layer have the same sign. Crossing the phase boundary, the electron spin polarization and the total spin polarization in the InAs/GaSb quantum well can change their signs.