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

Abstract

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.

Hole-spin initialization and relaxation times in InAs/GaAs quantum dots

“…49 By using the model given in Ref. 33, we are also able to calculate the hole-spin polarization level at negative time delay,…”

“…Lines are two fits with the model described in Ref. 33, assuming an inhomogeneity of Rabi angle values of 50% (solid line) or without inhomogeneity (dotted line), and taking the same sample parameters as used in Fig. 1.…”

“…1 represent the theoretical dependencies given by the model described in Ref. 33, for different values of the hole-spin relaxation time. We underline here that in our previous works we have shown that the hole states in the studied sample have a mixed character.…”

“…23,33 The efficient electron hf interaction imposes a coupling of both electron spin projections during the trion lifetime and, after emission of a circularly polarized photon, is at the origin of the hole-spin initialization. We will discuss in more detail the initialization mechanism in the last section of this article.…”

“…33. To probe the resident hole-spin polarization, we measured the photoinduced circular dichroism (PCD) in the QD sample.…”