Strict site-occupation constraint in 2d Heisenberg models and dynamical   mass generation in $QED_3$ at finite temperature
  We study the effect of site occupation in 2d quantum spin systems at finite temperature in a $\pi$-flux state description at the mean-field level. We impose each lattice site to be occupied by a single SU(2) spin. This is realized by means of a specific prescription. We consider the low-energy Hamiltonian which is mapped into a $QED_3$ Lagrangian of spinons. We compare the dynamically generated mass to the one obtained by means of an average site occupation constraint. 
Raoul Dillenschneider and Jean Richert