Magnetic polaron formation and exciton spin relaxation in single CdMnTe quantum dots

TL;DR

This study investigates how magnetic polarons form and how exciton spins relax in single CdMnTe quantum dots, revealing the influence of Mn concentration on formation times and spin dynamics.

Contribution

It provides new insights into the formation times of magnetic polarons and exciton spin relaxation in single quantum dots with varying Mn content, highlighting the role of Mn fluctuations.

Findings

Magnetic polaron formation times vary with Mn concentration.

Exciton spin relaxation accelerates as Mn content increases.

Spontaneous magnetization is influenced by Mn spin fluctuations.

Abstract

We study the formation dynamics of a spontaneous ferromagnetic order in single self-assembled CdMnTe quantum dots. By measuring time-resolved photoluminescence, we determine the formation times for QDs with Mn ion contents x varying from 0.01 to 0.2. At low x these times are orders of magnitude longer than exciton spin relaxation times evaluated from the decay of photoluminescence circular polarization. This allows us to conclude that the direction of the spontaneous magnetization is determined by a momentary Mn spin fluctuation rather than resulting from an optical orientation. At higher x, the formation times are of the same order of magnitude as found in previous studies on higher dimensional systems. We also find that the exciton spin relaxation accelerates with increasing Mn concentration.