On the Sz=0 excited states of an anisotropic Heisenberg chain

Abstract

The S^z=0 excited states of the anisotropic antiferromagnetic Heisenberg Hamiltonian H= Sigma _j=1^N(S_j^xS_j+1^x+S_j^yS_j+1^y+ rho S_j^zS_j+1^z) are studied when 0<or= rho <or=1. The original set of secular equations is reduced to a simpler one, which contains the parameters of excitations only. The energy-momentum dispersion is also found. It is shown that the typical low-lying excitations are either two-strings or not of string form. The simplest excitations are described in more detail.