Dimer-Quadrupolar Quantum Phase Transition in the Quasi-One-Dimensional   Heisenberg Model with Biquadratic Interaction
  The quasi-one-dimensional S=1 Heisenberg antiferromagnet with a biquadratic term is investigated at zero temperature by quantum Monte Carlo simulation. As the magnitude of the inter-chain coupling is increased, the system undergoes a phase transition from a spontaneously dimerized phase to a N\'eel ordered or spin nematic phase. The numerical results suggest the possibility of an unconventional second-order transition in which the symmetry group characterizing one phase is not a subgroup of the other. 
Kenji Harada, Naoki Kawashima, Matthias Troyer