Enhancement of Long Range Antiferromagnetic Order by Nonmagnetic Impurities in the Hubbard Model

TL;DR

This study demonstrates that nonmagnetic impurities in the two-dimensional Hubbard model can enhance long-range antiferromagnetic order by localizing dopants, leading to new insulating states at different fillings.

Contribution

It introduces a bimodal distribution of on-site interactions and shows how disorder stabilizes antiferromagnetic order away from half-filling using quantum Monte Carlo and dynamical mean-field theory.

Findings

Disorder stabilizes antiferromagnetic order off half-filling.

Gaps in compressibility and density of states appear at two fillings.

Localization of dopants on U=0 sites is key to the effect.

Abstract

The two-dimensional Hubbard model with a bimodal distribution of on-site interactions, P(U_i) = (1-f)\delta(U_i-U) + f\delta(U_i), is studied using a finite temperature quantum Monte Carlo technique and dynamical mean-field theory. We find long range antiferromagnetic order off half-filling is stabilized by the disorder, due to localization of the dopants on the U=0 sites. Whereas in the clean model there is a single gap at n=1, for nonzero f we find the compressibility and density of states exhibit gaps at two separate fillings.