Single-hole spin relaxation in a quantum dot

Using the photoluminescence of the trion feature as a monitor, we study experimentally the spin relaxation of the hole in self-assembled CdSe/ZnSe quantum dots. We observe two kinds of depolarization. The first one is due to an imperfect spin imprint of the circular photon polarization. The second transient depolarization is caused by the hole spin-flip in the Kramers degenerate trion doublet. At low temperature, the spin relaxation exhibits a slow component with a time constant longer than 10 ns. A considerable speedup takes place at higher temperature, reaching the sub nanosecond range at about 70 K. The activation energy is consistent with LO phonons.