Impurity spin textures across conventional and deconfined quantum critical points of two-dimensional antiferromagnets

TL;DR

This paper investigates the spin textures near impurities in two-dimensional antiferromagnets at quantum critical points, revealing universal behaviors and contrasting theoretical descriptions for different transition classes.

Contribution

It provides a unified field theory framework for impurity-induced spin textures across various quantum critical points in 2D antiferromagnets, including both conventional and deconfined transitions.

Findings

Universal spin distribution form across samples

Distinct field theories for different transition types

Impurity effects characterized by specific spin textures

Abstract

We describe the spin distribution in the vicinity of a non-magnetic impurity in a two-dimensional antiferromagnet undergoing a transition from a magnetically ordered Neel state to a paramagnet with a spin gap. The quantum critical ground state in a finite system has total spin S=1/2 (if the system without the impurity had an even number of S=1/2 spins), and recent numerical studies in a double layer antiferromagnet (K. H.Hoglund et al., cond-mat/0611418) have shown that the spin has a universal spatial form delocalized across the entire sample. We present the field theory describing the uniform and staggered magnetizations in this spin texture for two classes of antiferromagnets: (i) the transition from a Neel state to a paramagnet with local spin singlets, in models with an even number of S=1/2 spins per unit cell, which are described by a O(3) Landau-Ginzburg-Wilson field theory; and (ii) the transition from a Neel state to a valence bond solid, in antiferromagnets with a single S=1/2 spin per unit cell, which are described by a deconfined field theory of spinons.