ELECTRONIC POLARON EFFECTS IN MIXED-VALENCE AND HEAVY-FERMION MATERIALS

It is shown that the Coulomb interaction between f electrons and broad band electrons has a profound influence on the dynamical properties of an f hole in mixed valence and heavy fermion materials. At zero temperature the dynamics of the screening process contains an infrared divergence. The broadening of this divergence by temperature causes the motion of the f electrons to crossover from wave propagation to diffusion. This mechanism explains the observed dual nature of the f electrons, namely that at low temperatures they behave like a Fermi liquid, while at high temperatures they evolve into a lattice of localized magnetic moments.