Anisotropic frustrated Heisenberg model on the honeycomb lattice
  We investigate the ground-state phase diagram of an anisotropic Heisenberg model on the honeycomb lattice with competing interactions. We use quantum Monte Carlo simulations, as well as linear spin-wave and Ising series expansions, to determine the phase boundaries of the ordered magnetic phases. We find a region without any classical order in the vicinity of a highly frustrated point. Higher-order correlation functions in this region give no signal for long-range valence-bond order. The low-energy spectrum is derived via exact diagonalization to check for topological order on small-size periodic lattices. 
A. Kalz, M. Arlego, D. Cabra, A. Honecker, G. Rossini
cond-mat.str-el cond-mat.stat-mech