Vortex-enhanced alternating order around impurities in antiferromagnets

TL;DR

This paper investigates how vortex excitations influence the persistent alternating spin order around impurities in 2D antiferromagnets, revealing an enhancement near the Kosterlitz-Thouless transition through quantum Monte Carlo simulations.

Contribution

It introduces a vortex-based explanation for the impurity-induced alternating order in antiferromagnets, supported by simulations.

Findings

Alternating order around impurities remains temperature-independent over a wide range.

Vortex excitations enhance the alternating order near the Kosterlitz-Thouless transition.

Quantum Monte Carlo simulations confirm the vortex effect on spin order.

Abstract

It has been recently pointed out that the presence of a nonmagnetic impurity in a Heisenberg antiferromagnet generates an alternating order of the surrounding spins which is independent of temperature in a wide range. Quantum Monte Carlo simulations in the two-dimensional $S=1/2$ case confirmed this picture, but showed a counterintuitive enhancement of the alternating order around the Kosterlitz-Thouless transition. We propose here an explanation in terms of the effect of vortex excitations.