Protecting clean critical points by local disorder correlations

TL;DR

This paper demonstrates that certain quantum critical points can remain stable under locally correlated disorder, contrasting with uncorrelated disorder effects, and explores their properties through models and potential experiments.

Contribution

It introduces the concept that local disorder correlations can protect quantum critical points from instability typically caused by uncorrelated disorder.

Findings

Weak locally correlated disorder is irrelevant at quantum critical points.

Larger disorder leads to a line of critical points with increased entanglement entropy.

Proposes experimental setups in quantum magnetism and cold-atom systems.

Abstract

We show that a broad class of quantum critical points can be stable against locally correlated disorder even if they are unstable against uncorrelated disorder. Although this result seemingly contradicts the Harris criterion, it follows naturally from the absence of a random-mass term in the associated order-parameter field theory. We illustrate the general concept with explicit calculations for quantum spin-chain models. Instead of the infinite-randomness physics induced by uncorrelated disorder, we find that weak locally correlated disorder is irrelevant. For larger disorder, we find a line of critical points with unusual properties such as an increase of the entanglement entropy with the disorder strength. We also propose experimental realizations in the context of quantum magnetism and cold-atom physics.