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Incommensurate nodes in the energy spectrum of weakly coupled antiferromagnetic Heisenberg ladders

M. Azzouz, B. Dumoulin, A. Benyoussef

cond-matarXiv:cond-mat/9611049

Abstract

Heisenberg ladders are investigated using the bond-mean-field theory [M.Azzouz, Phys. Rev. B 48, 6136 (1993)]. The zero inter-ladder coupling energy gap, the uniform spin susceptibility and the nuclear magnetic resonance spin-relaxation rate are calculated as a function of temperature and magnetic field. For weakly coupled ladders, the energy spectrum vanishes at incommensurate wavevectors giving rise to nodes. As a consequence, the spin susceptibility becomes linear at low temperature. Our results for the single ladder successfully compare to experiments on SrCu2O3 and (VO)2P2O7 materials and new predictions concerning the coupling to the magnetic field are made.

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