Impurity-induced moments in underdoped cuprates

TL;DR

This paper investigates how nonmagnetic impurities induce local magnetic moments in underdoped cuprates, analyzing their interactions, screening effects, and comparison with experimental NMR data.

Contribution

It introduces a drone-fermion approach to study impurity effects and explores impurity interactions and Kondo screening in a spin-liquid context.

Findings

Impurities induce local magnetic moments near nonmagnetic defects.

An antiferromagnetic interaction between impurity moments is found on different sublattices.

Many impurities lead to screening of interactions via coherent-potential approximation.

Abstract

We examine the effect of a nonmagnetic impurity in a two-dimensional spin liquid in the spin-gap phase, employing a drone-fermion representation of spin-1/2 operators. The properties of the local moment induced in the vicinity of the impurity are investigated and an expression for the nuclear-magnetic- resonance Knight shift is derived, which we compare with experimental results. Introducing a second impurity into the spin liquid an antiferromagnetic interaction between the moments is found when the two impurities are located on different sublattices. The presence of many impurities leads to a screening of this interaction as is shown by means of a coherent-potential approximation. Further, the Kondo screening of an impurity-induced local spin by charge carriers is discussed.