Order-disorder transition in a two-layer quantum antiferromagnet.

We have studied the antiferromagnetic order – disorder transition occurring at T = 0 in a 2-layer quantum Heisenberg antiferromagnet as the interplane coupling is increased. Quantum Monte Carlo results for the staggered structure factor in combination with finite-size scaling theory give the critical ratio Jc = 2.51 ± 0.02 between the inter-plane and in-plane coupling constants. The critical behavior is consistent with the 3D classical Heisenberg universality class. Results for the uniform magnetic susceptibility and the correlation length at finite temperature are compared with recent predictions for the 2+1-dimensional nonlinear σ-model. The susceptibility is found to exhibit quantum critical behavior at temperatures significantly higher than the correlation length.