Non-perturbative Correlation Effects in Diluted Magnetic Semiconductors

TL;DR

This paper investigates non-perturbative carrier-impurity correlation effects in diluted magnetic semiconductors, revealing significant spin dynamics modifications, frequency renormalizations, and the formation of strongly correlated states at very low temperatures.

Contribution

It introduces a non-perturbative theoretical framework for understanding carrier-impurity correlations and their impact on spin dynamics in diluted magnetic semiconductors.

Findings

Carrier-impurity correlations cause spin transfer and frequency renormalization.

Logarithmic divergences in frequency renormalization are present in 2D systems but are mitigated by electron distribution.

Strongly correlated carrier-impurity states form at millikelvin temperatures.

Abstract

The effects of carrier-impurity correlations due to a Kondo-like spin-spin interaction in diluted magnetic semiconductors are investigated. These correlations are not only responsible for a transfer of spins between the carriers and the impurities, but also produce non-perturbative effects in the spin dynamics such as renormalization of the precession frequency of the carrier spins, which can reach values of several percent in CdMnTe quantum wells. In two-dimensional systems, the precession frequency renormalization for a single electron spin with defined wave vector shows logarithmic divergences similar to those also known from the Kondo problem in metals. For smooth electron distributions, however, the divergences disappear due to the integrability of the logarithm. A possible dephasing mechanism caused by the wave-vector dependence of the electron spin precession frequencies is found to be of minor importance compared to the spin transfer from the carrier to the impurity system. In the Markov limit of the theory, a quasi-equilibrium expression for the carrier-impurity correlation energy can be deduced indicating the formation of strongly correlated carrier-impurity states for temperatures in the mK range.