Vn. Kotov et al., Low-energy singlet and triplet excitations in the spin-liquid phase of thetwo-dimensional J(1)-J(2) model, PHYS REV B, 60(21), 1999, pp. 14613-14616
We analyze the stability of the spontaneously dimerized phase of the frustr
ated Heisenberg antiferromagnet-the J(1)-J(2) model-in two dimensions. The
lowest,tripler excitation, corresponding to breaking of a singlet bond, is
found to be stable in the region 0.38 less than or similar to J(2)/J(1)less
than or similar to 0.62. In addition we find a stable low-energy collectiv
e singlet mode, which reflects the spontaneous violation of the discrete sy
mmetry. The spontaneous dimerization vanishes at the point of second-order
quantum transition into the Neel ordered phase [(J(2)/J(1))(c1)approximate
to 0.38]. We argue that the disappearance of dimer order is related to the
vanishing of the singlet energy gap at the transition point. [S0163-1829(99
)04145-8].