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Various series expansions for a Heisenberg antiferromagnet model for SrCu2(BO3)2

Zheng Weihong, C. J. Hamer, J. Oitmaa

cond-mat.str-elarXiv:cond-mat/9811030

Abstract

We use a variety of series expansion methods at both zero and finite temperature to study an antiferromagnetic Heisenberg spin model proposed recently by Miyahara and Ueda for the quasi two-dimensional material SrCu2(BO3)2. We confirm that this model exhibits a first-order quantum phase transition at T=0 between a gapped dimer phase and a gapless Néel phase when the ratio x=J'/J of nearest and next-nearest neighbour interactions is varied, and locate the transition at xc=0.691(6). Using longer series we are able to give more accurate estimates of the model parameters by fitting to the high temperature susceptibility data.

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