Local magnetic impurities in the 2D quantum Heisenberg antiferromagnet

TL;DR

This paper investigates the effects of local magnetic impurities in the 2D quantum Heisenberg antiferromagnet, revealing that local magnetization remains finite with ferromagnetic bonds and identifying a ground state transition with impurity spins.

Contribution

Develops an analytic technique to study strong defect interactions and uncovers new behaviors of local magnetization and ground states in the presence of impurities.

Findings

Local magnetization remains finite with ferromagnetic bonds despite strong frustration.

Identification of a local ground state transition caused by impurity spins.

Comparison of analytic results with numerical exact diagonalization data.

Abstract

We consider the two-dimensional (2D) quantum Heisenberg antiferromagnet at zero temperature with two types of locally frustrating perturbations - an isolated ferromagnetic bond (FMB) and a quantum impurity spin, coupled symmetrically to the two sublattices. An analytic technique is developed to study strong defect-environment interaction. In the case of a FMB we find that, contrary to the previous linear spin-wave result, the local magnetization stays finite even for strong frustration. For an antiferromagnetic coupling of a quantum impurity spin with its environment, we find a local ground state transition. All our calculations are compared with numerical results from exact diagonalization on small clusters.