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.
Wenzel
Sandro
S
Institut für Theoretische Physik and Centre for Theoretical Sciences (NTZ), Universität Leipzig, Leipzig, Germany. wenzel@itp.uni-leipzig.de
Bogacz
Leszek
L
Janke
Wolfhard
W