Heavy Fermions due to Cooperative Effects of Coulomb and Electron–Phonon Interactions in the Two-Orbital Periodic Anderson Model

Abstract

Using the dynamical mean-field theory, we investigate the two-orbital periodic Anderson model including both the Coulomb interaction U between f -electrons and the electron–phonon interaction g which couple the local orbital fluctuations of f -electrons with Jahn–Teller phonons. It is found that the heavy fermion state caused by U is largely enhanced due to the effect of g . In the heavy fermion state for large U and g , both the orbital and lattice fluctuations are enhanced, while the charge (valence) and spin fluctuations are suppressed; this is a nonmagnetic origin of the heavy fermions. The effect of the mass enhancement for the case with twofold-degenerate phonon mode is larger than that for one phonon mode. The obtained results show a possible nonmagnetic origin of the heavy fermion state recently observed in SmOs 4 Sb 12 .