Hole spin relaxation in p-type (111) GaAs quantum wells

Hole spin relaxation in p-type (111) GaAs quantum wells is investigated for cases in which only the lowest hole subband, which is heavy-hole like in (111) GaAs/AlAs and light-hole like in (111) GaAs/InP quantum wells, is relevant. The subband Lowdin perturbation method is applied to obtain the effective Hamiltonian including the Dresselhaus and Rashba spin-orbit couplings. Under a proper gate voltage, the total in-plane effective magnetic field in (111) GaAs/AlAs quantum wells can be strongly suppressed in the entire momentum space, while that in (111) GaAs/InP quantum wells can be suppressed only on a special momentum circle. The hole spin relaxation due to the D'yakonov-Perel' and Elliott-Yafetmechanisms is calculated by means of the fully microscopic kinetic spin Bloch equation approach with all the relevant scatterings explicitly included. For (111) GaAs/AlAs quantum wells, extremely long heavy-hole spin relaxation time (up to hundreds of nanoseconds) is predicted. In particular, we predict a pronounced peak in the gate-voltage dependence of the heavy-hole spin relaxation time due to the D'yakonov-Perel' mechanism. This peak originates from the suppression of the unique inhomogeneous broadening in (111) GaAs/AlAs quantum wells. Moreover, the Elliott-Yafet mechanism influences the spin relaxation only around the peak area. In (111) GaAs/InP quantum wells, a mild peak, similar to the case for electrons in (111) GaAs quantum wells, is also predicted by the gate-voltage dependence of the light-hole spin relaxation time. The contribution of the Elliott-Yafet mechanism is found to always be negligible in this case.