Evidence of Unconventional Universality Class in a TwoDimensional Dimerized Quantum Heisenberg Model 

Sandro Wenzel 
ITP Leipzig 

le Thursday 22 May 2008 à 10h00 
Salle de séminaire du groupe de Physique Statistique 


The twodimensional JJ' 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 orderdisorder quantum phase transition in the JJ' model is determined as alpha=2.5196(2) by finitesize scaling for up to N=96x96 quantum spins. By comparing six dimerized models we show, contrary to the current believe, that the critical exponents of the JJ' model are not in agreement with the threedimensional classical Heisenberg universality class which gives support to the notion of nontrivial critical excitations at the quantum critical point. 
