Eur. Phys. J. B 53, 11-18 (2006)
https://doi.org/10.1140/epjb/e2006-00342-3

Stable particles in anisotropic spin-1 chains

¹ Dipartimento di Fisica dell'Università di Bologna, viale Berti-Pichat, 6/2, 40127 Bologna, Italia
² INFN, Sezione di Bologna, viale Berti-Pichat, 6/2, 40127 Bologna, Italia
³ CNR-INFM, Unità di Ricerca di Bologna, viale Berti-Pichat, 6/2, 40127 Bologna, Italia
⁴ CNISM, Sezione di Bologna, viale Berti-Pichat, 6/2, 40127 Bologna, Italia
⁵ Dipartimento di Fisica dell'Università di Bologna, via Irnerio 46, 40126 Bologna, Italia

Corresponding author: ^a cristian.degliesposti@unibo.it

Received: 30 May 2006
Published online: 6 September 2006

Abstract

Motivated by field-theoretic predictions we investigate the stable excitations that exist in two characteristic gapped phases of a spin-1 model with Ising-like and single-ion anisotropies. The sine-Gordon theory indicates a region close to the phase boundary where a stable breather exists besides the stable particles, that form the Haldane triplet at the Heisenberg isotropic point. The numerical data, obtained by means of the Density Matrix Renormalization Group, confirm this picture in the so-called large-D phase for which we give also a quantitative analysis of the bound states using standard perturbation theory. However, the situation turns out to be considerably more intricate in the Haldane phase where, to the best of our data, we do not observe stable breathers contrarily to what could be expected from the sine-Gordon model, but rather only the three modes predicted by a novel anisotropic extension of the Non-Linear Sigma Model studied here by means of a saddle-point approximation.