Relaxation of hole spins in quantum dots via two-phonon processes.

We investigate theoretically spin relaxation in heavy-hole quantum dots in low external magnetic fields. We demonstrate that two-phonon processes and spin-orbit interaction are experimentally relevant and provide an explanation for the recently observed saturation of the spin-relaxation rate in heavy-hole quantum dots with vanishing magnetic fields. We propose further experiments to identify the relevant spin-relaxation mechanisms in low magnetic fields.