Spin-wave spectra of a Kagome stripe

¹  Max-Planck-Institut für Physik Komplexer Systeme - D-01187 Dresden, Germany
²  Department of Physics, University of Wisconsin - Madison, WI 53706, USA

Received: 9 August 2007
Accepted: 17 October 2007

Abstract

We study ground-state degeneracy and spin-wave excitations in a 1D version of a Kagome antiferromagnet —a Heisenberg antiferromagnet on a Kagome stripe. We show that for nearest-neighbor interaction, the classical ground state is infinitely degenerate. For any spin configuration from the degenerate set, the classical spin-wave spectrum contains, in addition to Goldstone modes, a branch of zero-energy excitations, and a zero mode in another branch. We demonstrate that the interactions beyond nearest neighbors lift the degeneracy, eliminate a zero mode, and give a finite dispersion to formerly zero-energy branch, leaving only Goldstone modes as zero-energy excitations.