Optically Driven Spin Memory in $n$-Doped InAs-GaAs Quantum Dots

We show that the spin state of the resident electron in an $n$-doped self-assembled InAs-GaAs quantum dot can be written and read using nonresonant, circularly polarized optical pumping. A simple theoretical model is presented and accounts for the remarkable dynamics producing counterpolarized photoluminescence.

Figure 1

Upper curves: polarization-resolved photoluminescence spectra at $T=10\mathrm{K}$ of the $n$-doped sample under WL excitation with ${\sigma }^{+}$-polarized light for two different powers. Lower curves: corresponding circular polarization ratios together with the undoped sample’s ratios measured under equivalent excitation conditions.

Figure 2

Top: time-resolved photoluminescence detected at 1.15 eV under circularly polarized excitation at 1.44 eV of the $n$-doped QD sample. The inset shows a blowup of the fast dynamics at short times. Bottom: the corresponding circular polarization is shown (dark line), as well as the polarization in the presence of a counterpolarized pump pulse 10 ns earlier (grey line).

Figure 3

Hot trion fine structure in a symmetrical QD. ${\tilde{\Delta }}_{\mathrm{S}\mathrm{\text{−}}\mathrm{P}}$ is the energy separation between excited and ground trion states, corrected by the direct Coulomb terms. The electron-hole exchange interaction (${\Delta }_0$) slightly splits the triplet-based states.

Figure 4

Circular polarization of the probe luminescence induced by a 4-ns ${\sigma }^{+}$ pump pulse. For the $n$-doped sample, the spin orientation decay time of the resident electrons is about 15 ns.