Griffiths phase in diluted magnetic semiconductors

TL;DR

This paper investigates disorder effects near the ferromagnetic transition in diluted magnetic semiconductors, deriving an effective Hamiltonian that reveals a Griffiths phase with unique susceptibility properties.

Contribution

It introduces a novel effective polaron Hamiltonian and demonstrates the existence of a Griffiths phase with non-perturbative susceptibility effects in localized regimes.

Findings

Identification of Griffiths phase above the ferromagnetic transition

Derivation of long-time susceptibility with pseudo-scaling behavior

Expression of dynamic critical exponent via percolation indices

Abstract

We study the effects of disorder in the vicinity of the ferromagnetic transition in a diluted magnetic semiconductor in the strongly localized regime. We derive an effective polaron Hamiltonian, which leads to the Griffiths phase above the ferromagnetic transition point. The Griffiths-McCoy effects yield non-perturbative contributions to the dynamic susceptibility. We explicitly derive the long-time susceptibility, which has a pseudo-scaling form, with the dynamic critical exponent being expressed through the percolation indices.