Monte Carlo approach to the dynamical coherent-potential approximation in metallic magnetism.

Abstract

A Monte Carlo approach to the dynamical coherent-potential approximation (CPA) has been proposed on the basis of the functional-integral method to deal with the dynamical spin fluctuations in the Gutzwiller-Hubbard model. The functional integral on a site in the effective medium is replaced by the ${\mathit{N}}_{\ensuremath{\xi}}$-fold integral, which is evaluated by the Monte Carlo method. Numerical calculations have been performed up to ${\mathit{N}}_{\ensuremath{\xi}}$=64 for intermediate Coulomb interaction strength in the paramagnetic state. It is demonstrated that the present theory recovers the amplitude of local moment, reduces the effective Coulomb interaction, and leads to more Fermi-liquid-like momentum distribution when they are compared with the static approximation. Furthermore, the single-particle excitation spectra calculated by a numerical analytic continuation are shown to have some shoulders due to many-body excitations.