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

TL;DR

This paper investigates the spin dynamics of a Cr$^+$-doped quantum dot using resonant photoluminescence, revealing spin relaxation mechanisms, optical control of spin states, and the influence of phonons on the spin system.

Contribution

It provides new insights into the spin relaxation channels and optical control of Cr$^+$ spins in quantum dots through resonant PL techniques.

Findings

Resonant PL intensity is affected by optical pumping of the hole-Cr$^+$ complex.

The Cr$^+$ spin state can be partially erased by non-resonant excitation.

Optical excitation influences the effective temperature of the spin system via phonon generation.

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 $\vert S_z \vert$. 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.