Dynamical coherent-potential approximation to the magnetism in a correlated electron system

Abstract

A dynamical coherent-potential approximation for correlated electron systems has been developed on the basis of a functional integral method and the harmonic approximation that neglects the mode-mode couplings between dynamical potentials. Within the single-site approximation, the theory becomes exact in the high-temperature limit, reproduces the results of the second-order perturbation theory for small Coulomb interaction, and takes into account the terms that are needed to describe the strongly correlated limit. The theory interpolates between the weak Coulomb interaction limit and the atomic limit. An approximation scheme has been developed to implement the numerical calculations. The model calculations have been performed for the electron number $n=1.44$ (bcc) and $n=1.80$ (fcc). In the case of the former, the magnetization vs temperature curve and the Curie-Weiss susceptibility are obtained. It is found that the Curie temperature is reduced by a factor of 2 due to dynamical effects. In the case of the latter, the dynamical effects are found to make the ferromagnetism unstable. In both cases a many-body satellite peak and a band narrowing are found in the paramagnetic density of states for the single-particle excitation energy.