The two-dimensional $J\mathrm{\text{−}}{J}^{\prime }$ dimerized quantum Heisenberg model is studied on the square lattice by means of (stochastic series expansion) quantum Monte Carlo simulations as a function of the coupling ratio $\alpha =J^{\prime }/J$. The critical point of the order-disorder quantum phase transition in the $J\mathrm{\text{−}}{J}^{\prime }$ model is determined as ${\alpha }_c=2.5196(2)$ by finite-size scaling for up to approximately 10 000 quantum spins. By comparing six dimerized models we show, contrary to the current belief, that the critical exponents of the $J\mathrm{\text{−}}{J}^{\prime }$ model are not in agreement with the three-dimensional classical Heisenberg universality class. This lends support to the notion of nontrivial critical excitations at the quantum critical point.

• Received 16 May 2008

DOI:https://doi.org/10.1103/PhysRevLett.101.127202