Double-layer Heisenberg antiferromagnet at finite temperature: Brueckner theory and quantum Monte Carlo simulations

The double-layer Heisenberg antiferromagnet with intra- and interlayer couplings J and J(perpendicular to) exhibits a zero-temperature quantum phase transition between a quantum disordered dimer phase for g>g(c) and a Neel phase with long-range antiferromagnetic order for g0 and g-->g(c), our analytical results for the specific heat and the magnetic susceptibility coincide with those previously obtained within the nonlinear sigma model approach for N-->infinity. Our quantum Monte Carlo simulations extend to significantly lower temperatures than previously, allowing us to obtain accurate results for the asymptotic quantum critical behavior. We also obtain an improved estimate for the critical coupling: g(c) = 2.525 +/- 0.002.