Effects of disorder in two-dimensional quantum antiferromagnets

TL;DR

This paper investigates how disorder affects two-dimensional quantum antiferromagnets, revealing that disorder induces a transition from gapped to gapless spin excitations and alters correlation decay behavior.

Contribution

It provides a theoretical analysis of disorder effects using the nonlinear sigma model, highlighting the transition from exponential to power-law decay in spin correlations.

Findings

Disorder causes spin excitations to become gapless.

Correlation functions change from exponential to power-law decay.

Disorder influences the behavior of skyrmion topological excitations.

Abstract

We study the effects of disorder in two-dimensional quantum antiferromagnets on a square lattice, within the nonlinear sigma model approach, by using of a random distribution of spin stiffnesses or zero-temperature-spin-gaps, respectively, in the renormalized classical and quantum disordered phases. The quenched staggered magnetic susceptibility at low temperatures is evaluated in each case. The large distance behavior of the quenched spin correlation function is also obtained in the quantum disordered phase. Disorder is shown to introduce a change from exponential to power-law decay in these functions, indicating that the spin excitations become gapless, in spite of the fact that the system is in a disorder state. A comparison is made with the dual behavior of skyrmion topological excitations in the renormalized classical phase.