Protecting clean critical points by local disorder correlations

¹ Instituto de Física de São Carlos, Universidade de São Paulo - C.P. 369, São Carlos, São Paulo 13560-970, Brazil
² Laboratoire de Physique des Solides, Université Paris-Sud, UMR-8502 CNRS - 91405 Orsay, France, EU
³ Instituto de Física, Universidade de São Paulo - C.P. 66318, São Paulo 05314-970, Brazil
⁴ Department of Physics, Missouri University of Science and Technology - Rolla, MO 65409, USA

^a hoyos@ifsc.usp.br

Received: 17 December 2010
Accepted: 17 January 2011

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.