Quantum phase transitions in disordered dimerized quantum spin models and the Harris criterion

TL;DR

This study uses quantum Monte Carlo simulations to investigate how disorder affects quantum phase transitions in dimerized quantum spin models, finding that the transition remains in the 3D O(3) universality class despite violations of the Harris criterion.

Contribution

The paper demonstrates that certain disordered dimerized quantum spin models do not deviate from the expected universality class, challenging the applicability of the Harris criterion in these cases.

Findings

Transition remains in 3D O(3) universality class despite disorder

No observed deviations from expected critical exponents

Discussion of conditions where nu<1 is possible

Abstract

We use quantum Monte Carlo simulations to study effects of disorder on the quantum phase transition occurring versus the ratio g=J/J' in square-lattice dimerized S=1/2 Heisenberg antiferromagnets with intra- and inter-dimer couplings J and J'. The dimers are either randomly distributed (as in the classical dimer model), or come in parallel pairs with horizontal or vertical orientation. In both cases the transition violates the Harris criterion, according to which the correlation-length exponent should satisfy nu >= 1. We do not detect any deviations from the three-dimensional O(3) universality class obtaining in the absence of disorder (where nu = 0.71). We discuss special circumstances which allow nu<1 for the type of disorder considered here.