Solitons and magnons in quantum spin chains

Abstract

The z-component dynamical spin correlation function Szz(q,w) of the s=1/2 anisotropic XY chain is calculated exactly in the fermion representation. Szz consists of two parts: one (Sm) represents two fermion excitations and the other (Ss) describes scattering from thermally excited fermions. In the continuum limit, Ss has the structure of the solitonic part of a classical sine-Gordon correlation function, but the soliton form factor is modified by quantum effects. Sm has similarities with the spin-wave continuum form of Szz an isotropic spin chains. The continuum results are compared with those for a discrete chain.