Hole and trion spin dynamics in quantum dots under excitation by a train of circularly polarized pulses

We have performed pump-probe experiments in p-doped InAs/GaAs quantum dots leading to the all-optical initialization and readout of hole spins. In order to describe these experiments, we have modelized the interconnected dynamics of the photoelectron spin and the resident hole spin, triggered through the optical excitation by a train of short pulses. A complete description of this spin dynamics is obtained by including the hyperfine coupling as the common decoherence mechanism for the electron and hole spins. Periodic excitation conditions for arbitrary values of the pump power and the external magnetic field are also included in the model. In particular, a good agreement concerning the temporal behavior of the photoinduced circular dichroism is obtained for zero or low magnetic fields. When the applied magnetic field screens the hole-hyperfine interaction, we show that the agreement between the experimental and calculated time-dependent curves requires an additional relaxation mechanism for holes with a characteristic time in the microsecond range.