Spin-wave excitation spectra and spectral weights in square lattice antiferromagnets

TL;DR

This paper calculates the spin-wave excitation spectra and spectral weights in square lattice S=1/2 Heisenberg-Ising antiferromagnets using a new series expansion method, revealing detailed spectral features and weight distributions.

Contribution

It introduces a novel series expansion technique to accurately compute excitation spectra and spectral weights in quantum antiferromagnets, improving upon previous models.

Findings

The Heisenberg model spectrum closely matches but differs from classical predictions.

The spin-wave velocity renormalization is approximately 1.18.

Spectral weights for single- and multi-magnon contributions are mapped across the Brillouin zone.

Abstract

Using a recently developed method for calculating series expansions of the excitation spectra of quantum lattice models, we obtain the spin-wave spectra for square lattice, $S=1/2$ Heisenberg-Ising antiferromagnets. The calculated spin-wave spectrum for the Heisenberg model is close to but noticeably different from a uniformly renormalized classical (large-$S$) spectrum with the renormalization for the spin-wave velocity of approximately $1.18$. The relative weights of the single-magnon and multi-magnon contributions to neutron scattering spectra are obtained for wavevectors throughout the Brillouin zone.