Dynamical Cluster Approximation for the Periodic Anderson Model: Competition between Local and Non-local Correlations

The single particle excitation spectrum of the periodic Anderson model in two dimensions is calculated by using the dynamical cluster approximation (DCA). The DCA method is an extention of the dynamical mean field approximation, that is, the short range inter-site correlations are restored by considering the cluster. For the half filling model there is no sharp coherence peak at the Fermi level due to the antiferromagnetic Ruderman-Kittel-Kasuya-Yosida (RKKY)-like interaction. When the filling of the conduction electron band is small, there is a sharp coherence peak. It can be explaind that the effect of the RKKY-like interaction is weaker than that for the half filling model or the RKKY-like interaction changes to the ferromagnetic one. For the intermediate filling model the intensity of the coherence peak becomes very small.