Dynamical Properties of a Haldane Gap Antiferromagnet

TL;DR

This paper investigates the dynamic spin correlations in a spin-one antiferromagnetic chain with anisotropy, using exact diagonalization and variational methods, explaining experimental neutron scattering results.

Contribution

It provides a detailed analysis of excitations and continuum features in a Haldane gap antiferromagnet, clarifying the nature of excitations with theoretical calculations.

Findings

Single-mode approximation accurately describes dynamical properties.

Existence of a two-particle continuum near zero wavevector.

Results fully explain neutron scattering experiments on NENP.

Abstract

We study the dynamic spin correlation function of a spin one antiferromagnetic chain with easy-plane single-ion anisotropy. We use exact diagonalization by the Lancz\H os method for chains of lengths up to N=16 spins. We show that a single-mode approximation is an excellent description of the dynamical properties. A variational calculation allows us to clarify the nature of the excitations. The existence of a two-particle continuum near zero wavevector is clearly seen both in finite-size effects and in the dynamical structure factor. The recent neutron scattering experiments on the quasi-one-dimensional antiferromagnet NENP are fully explained by our results.