Non-Markovian spin transfer dynamics in magnetic semiconductors despite short memory times

TL;DR

This paper investigates spin transfer in magnetic semiconductors, revealing that short memory times do not always justify Markovian approximations, especially in low-dimensional systems where quantum effects cause deviations.

Contribution

It demonstrates that quantum kinetic effects lead to non-Markovian spin dynamics in quantum wells and wires, challenging the applicability of Markovian rate equations in these systems.

Findings

Markovian rate equations work well for bulk systems

Quantum wells and wires show deviations from Markovian predictions

Oscillations and overshoot phenomena are caused by energy redistributions

Abstract

A quantum kinetic theory of the spin transfer between carriers and Mn atoms in a Mn doped diluted magnetic semiconductor is presented. It turns out that the typical memory time associated with these processes is orders of magnitude shorter than the time scale of the spin transfer. Nevertheless, Markovian rate equations, which are obtained by neglecting the memory, work well only for bulk systems. For quantum wells and wires the quantum kinetic results qualitatively deviate from the Markovian limit under certain conditions. Instead of a monotonic decay of an initially prepared excess electron spin, an overshoot or even coherent oscillations are found. It is demonstrated that these features are caused by energetic redistributions of the carriers due to the energy-time uncertainty.