Spin dynamics of positively charged excitons in Cr+ -doped quantum dots probed by resonant photoluminescence

Abstract

We study the dynamics of the spin system that consists of a positively charged II-VI semiconductor quantum dot doped with a single ${\mathrm{Cr}}^{+}$ ion. The resonant photoluminescence (PL) of the positively charged exciton coupled with the ${\mathrm{Cr}}^{+}$ spin is used to analyze the main spin relaxation channels. The intensity of the resonant PL is reduced by an optical pumping of the spin of the resident hole-${\mathrm{Cr}}^{+}$ complex that can be seen as a nanomagnet. The spin memory can be partially erased by a nonresonant optical excitation. This leads to an increase of the resonant PL signal. The resonant PL is cocircularly polarized and corresponds to relaxation channels that conserve the ${\mathrm{Cr}}^{+}$ spin $|{S}_{z}|$. The observation in the resonant-PL excitation spectra of optical transitions with a change of the ${\mathrm{Cr}}^{+}$ spin permits to determine the magnetic anisotropy of the magnetic atom. Optical pumping, autocorrelation measurements, and the power dependence of the PL intensity distribution show that the effective temperature of the hole-${\mathrm{Cr}}^{+}$ spin system is affected by the optical excitation through the local generation of phonons.