Phonon impact on the dynamics of resonantly excited and hot excitons in diluted magnetic semiconductors

TL;DR

This study explores how phonons influence exciton dynamics in diluted magnetic semiconductors, revealing that phonons significantly redistribute exciton momenta at high temperatures but have minimal impact on spin dynamics dominated by magnetic impurities.

Contribution

It extends quantum kinetic models to include phonon scattering, providing new insights into exciton behavior in magnetic semiconductors under various conditions.

Findings

Phonons cause notable momentum redistribution at high temperatures.

Exciton spin lifetime increases by about tenfold for hot excitons.

Quantum kinetic effects are suppressed after resonant optical excitation.

Abstract

Phonons are well known to be the main mechanism for the coupling between bright and dark excitons in nonmagnetic semiconductors. Here, we investigate diluted magnetic semiconductors where this process is in direct competition with the scattering at localized magnetic impurities. To this end, a recently developed quantum kinetic description of the exciton spin dynamics in diluted magnetic semiconductor quantum wells is extended by the scattering with longitudinal acoustic phonons. A strong phonon impact is found in the redistribution of exciton momenta on the exciton parabola that becomes especially prominent for high temperatures and exciton distributions further away from the exciton resonance which are optically dark. Despite their impact on the energetic redistribution, acoustic phonons virtually do not affected the exciton spin dynamics as the exciton-impurity interaction always dominates. Furthermore, it turns out that the exciton spin lifetime increases by roughly one order of magnitude for nonequilibrium hot exciton distributions and, in addition, pronounced quantum kinetic signatures in the exciton spin dynamics appearing after resonant optical excitation are drastically reduced.