Disorder and Impurities in Hubbard-Antiferromagnets

TL;DR

This paper investigates how different types of disorder and impurities affect antiferromagnetic order in the Hubbard model, revealing conditions under which disorder enhances or destroys magnetic order and alters electronic properties.

Contribution

It provides a comprehensive analysis of disorder effects on correlated antiferromagnets using quantum Monte Carlo and dynamical mean-field theory, highlighting novel disorder-induced phenomena.

Findings

Weak disorder can enhance AF order via delocalization or carrier binding.

Strong disorder or high impurity concentration destroys AF order.

Impurities can close the charge gap and induce AF phases without a gap.

Abstract

We study the influence of disorder and randomly distributed impurities on the properties of correlated antiferromagnets. To this end the Hubbard model with (i) random potentials, (ii) random hopping elements, and (iii) randomly distributed values of interaction is treated using quantum Monte Carlo and dynamical mean-field theory. In cases (i) and (iii) weak disorder can lead to an enhancement of antiferromagnetic (AF) order: in case (i) by a disorder-induced delocalization, in case (iii) by binding of free carriers at the impurities. For strong disorder or large impurity concentration antiferromagnetism is eventually destroyed. Random hopping leaves the local moment stable but AF order is suppressed by local singlet formation. Random potentials induce impurity states within the charge gap until it eventually closes. Impurities with weak interaction values shift the Hubbard gap to a density off half-filling. In both cases an antiferromagnetic phase without charge gap is observed.