TP1, Universitaet Wuerzburg
An efficient method of describing non-local correlation effect in strongly correlated system can be achieved by introducing an auxiliary variable in the dynamical mean-field theory. The new fermions are dual to the original ones and represent the effectively weakly coupled quasiparticles. Dynamical mean field theory is taken as the zero-th approximation in this method. The exact relation between the dual and lattice fermions allows us to determine the latter one by performing a perturbative expansion in the dual variables, where the effective interaction is the local vertex of the lattice fermions. It is shown that the good agreement with lattice QMC calculation can be reproduced by the lowest-order diagram. In contrast to the conventional perturbative method, even in the strong coupling regime the convergence of this method is fast. In this presentation, I will show the details of this method and some comparisons with the lattice QMC results. As an application, some results on a triangular lattice calculation will be given.