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arXiv:cond-mat/9903154 · Physical review. B, Condensed matter

Low-energy singlet and triplet excitations in the spin-liquid phase of the two-dimensional J1−J2 model

Valeri N. Kotov, J. Oitmaa, Oleg P. Sushkov, Zheng Weihong

Published Dec 1, 1999• 83 citations
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Abstract

We analyze the stability of the spontaneously dimerized phase of the frustrated Heisenberg antiferromagnet---the ${J}_{1}{\ensuremath{-}J}_{2}$ model---in two dimensions. The lowest triplet excitation, corresponding to breaking of a singlet bond, is found to be stable in the region $0.38\ensuremath{\lesssim}{J}_{2}{/J}_{1}\ensuremath{\lesssim}0.62.$ In addition we find a stable low-energy collective singlet mode, which reflects the spontaneous violation of the discrete symmetry. The spontaneous dimerization vanishes at the point of second-order quantum transition into the N\'eel ordered phase $[{(J}_{2}{/J}_{1}{)}_{c1}\ensuremath{\approx}0.38].$ We argue that the disappearance of dimer order is related to the vanishing of the singlet energy gap at the transition point.

DOI
10.1103/physrevb.60.14613

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