Long-range ferromagnetic correlations between Anderson impurities in a semiconductor host

TL;DR

This study uses quantum Monte Carlo simulations to analyze ferromagnetic correlations between impurities in a semiconductor, revealing extended interaction ranges and implications for designing high-temperature dilute magnetic semiconductors.

Contribution

It demonstrates that the two-impurity Anderson model can explain ferromagnetic correlations in dilute magnetic semiconductors like Ga_{1-x}Mn_xAs, with insights into the effects of Fermi level positioning.

Findings

Impurity spins show long-range ferromagnetic correlations.

Correlation range is maximized when the Fermi level is above the valence band top.

Results align with experimental data on Ga_{1-x}Mn_xAs and suggest pathways for higher Curie temperature materials.

Abstract

We study the two-impurity Anderson model for a semiconductor host using the quantum Monte Carlo technique. We find that the impurity spins exhibit ferromagnetic correlations with a range which can be much more enhanced than in a half-filled metallic band. In particular, the range is longest when the Fermi level is located above the top of the valence band and decreases as the impurity bound state becomes occupied. Comparisons with the photoemission and optical absorption experiments suggest that this model captures the basic electronic structure of Ga_{1-x}Mn_xAs, the prototypical dilute magnetic semiconductor (DMS). These numerical results might also be useful for synthesizing DMS or dilute-oxide ferromagnets with higher Curie temperatures.