Optical orientation of hole magnetic polarons in (Cd,Mn)Te/(Cd,Mn,Mg)Te quantum wells

TL;DR

This study investigates the optically induced spin polarization of magnetic polarons in (Cd,Mn)Te/(Cd,Mn,Mg)Te quantum wells, revealing long-lived nonoscillating polarization linked to hole magnetic polarons and their temperature and field-dependent dynamics.

Contribution

It provides new insights into the optical orientation and spin dynamics of equilibrium magnetic polarons involving resident holes in quantum wells.

Findings

Detection of long-lived (up to 60 ns) nonoscillating spin polarization.

Identification of magnetic polaron dynamics originating from unexcited polarons.

Demonstration that polaron spin relaxation is influenced by temperature and magnetic field.

Abstract

The optically induced spin polarization in (Cd,Mn)Te/(Cd,Mn,Mg)Te diluted-magnetic-semiconductor quantum wells is investigated by means of picosecond pump-probe Kerr rotation. At 1.8 K temperature, additionally to the oscillatory signals from photoexcited electrons and Manganese spins precessing about an external magnetic field, a surprisingly long-lived (up to 60 ns) nonoscillating spin polarization is detected. This polarization is related to optical orientation of equilibrium magnetic polarons involving resident holes. The suggested mechanism for the optical orientation of the equilibrium magnetic polarons indicates that the detected polaron dynamics originates from unexcited magnetic polarons. The polaron spin dynamics is controlled by the anisotropic spin structure of the heavy-hole resulting in a freezing of the polaron magnetic moment in one of the two stable states oriented along the structure growth axis. Spin relaxation between these states is prohibited by a potential barrier, which depends on temperature and magnetic field. The magnetic polaron relaxation is accelerated with increasing temperature and in magnetic field.