Local Enhancement of Antiferromagnetic Correlations by Nonmagnetic Impurities

TL;DR

This paper explains how nonmagnetic impurities locally enhance antiferromagnetic correlations in various spin systems, attributing it to resonating-valence-bond characteristics, with numerical and experimental implications.

Contribution

It introduces a unified framework demonstrating that short-range antiferromagnetic enhancement near impurities is due to resonating-valence-bond properties, supported by numerical results across multiple systems.

Findings

Local enhancement occurs in diverse spin systems.

Resonating-valence-bond character explains the phenomenon.

Independent of long-range spin correlation behavior.

Abstract

The local enhancement of antiferromagnetic correlations near vacancies observed in a variety of spin systems is analyzed in a single framework. Variational calculations suggest that the resonating-valence-bond character of the spin correlations at short distances is responsible for the enhancement. Numerical results for uniform spin chains, with and without frustration, dimerized chains, ladders, and two dimensional clusters are in agreement with our conjecture. This short distance phenomenon occurs independently of the long distance behavior of the spin correlations in the undoped system. Experimental predictions for a variety of compounds are briefly discussed.