Evidence for an unconventional universality class from a two-dimensional dimerized quantum heisenberg model.
The two-dimensional J-J' 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'/J. The critical point of the order-disorder quantum phase transition in the J-J' 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-J' 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.
Institut für Theoretische Physik and Centre for Theoretical Sciences (NTZ), Universität Leipzig, Leipzig, Germany. wenzel@itp.uni-leipzig.de
Sandro
S
Wenzel
Leszek
L
Bogacz
Wolfhard
W
Janke