Dimer order with striped correlations in the J(1)-J(2) Heisenberg model

Ground-state energies for plaquette and dimer order in the J(1)-J(2) square -lattice spin-half Heisenberg model are compared using series expansion met hods. We find that these energies are remarkably close to each other at int ermediate values of J(2)/J(1), where the model is believed to have a quantu m disordered ground state. They join smoothly with those obtained from the Ising expansions for the two-sublattice Neel state at J(2)/J(1) approximate to 0.4, suggesting a second-order transition from a Neel state to a quantu m disordered state, whereas they cross the energy for the four-sublattice o rdered state at J(2)/J(1) approximate to 0.6 at a large angle, implying a f irst-order transition to the four-sublattice magnetic state. The strongest evidence that the plaquette phase is not realized in this model comes from the analysis of the series for the singlet and triplet excitation spectra, which suggest an instability in the plaquette phase. Thus our study support s the recent work of Kotov et nl., which presents a strong picture for colu mnar dimer order in this model. We also discuss the striped nature of spin correlations in this phase, with substantial resonance all along columns of dimers. [S0163-1829(99)06433-4].