Rattling-Induced Heavy Fermion State in the Anharmonic Holstein Model

Abstract

We investigate the heavy fermion states in the half-filled anharmonic Holstein model by using the dynamical mean-field theory combined with the exact diagonalization method at low temperatures down to 1/10 4 of the conduction bandwidth. For the weak anharmonic cases with single-well or shallow double-well potentials, the bipolaronic first order phase transition takes place at a critical value of the electron–phonon coupling below a critical temperature as recently observed in the harmonic Holstein model. On the other hand, for the strong anharmonic case with deep double-well potential, the bipolaronic transition is suppressed and changes to a crossover where the heavy fermion state with a large effective mass is realized due to the effect of largely anharmonic local oscillations called rattling.