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 consist of a positively charged II-VI semiconductor quantum dot doped with a single Cr + ion. The resonant photoluminescence (PL) of the positively charged exciton coupled with the 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-Cr + complex that can be seen as a nano-magnet. The spin memory can be partially erased by a non-resonant optical excitation. This leads to an increase of the resonant PL signal. The resonant PL is co-circularly polarized and corresponds to relaxation channels that conserve the Cr + spin |Sz|. The observation in the resonant-PL excitation spectra of optical transitions with a change of the Cr + spin permits to determine the magnetic anisotropy of the magnetic atom. Optical pumping, auto-correlation measurements and the power dependence of the PL intensity distribution show that the effective temperature of the hole-Cr + spin system is affected by the optical excitation through the local generation of phonons.