Spin-wave spectra of a Kagome stripeA. Donkov1 and A. V. Chubukov2
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 in final form 17 October 2007; published December 2007
published online 8 November 2007
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.
75.10.Pq - Spin chain models.
75.30.Ds - Spin waves.
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