Polaron Crossover and Bipolaronic Metal-Insulator Transition in the Half-Filled Holstein Model

M. Capone and S. Ciuchi

Phys. Rev. Lett. 91, 186405 – Published 30 October 2003

Abstract

The formation of a finite-density polaronic state is analyzed in the context of the Holstein model using the dynamical mean-field theory. The spinless and spinful fermion cases are compared to disentangle the polaron crossover from the bipolaron formation. The exact solution of dynamical mean-field theory is compared with weak-coupling perturbation theory, noncrossing (Migdal), and vertex correction approximations. We show that polaron formation is not associated with a metal-insulator transition, which is instead due to bipolaron formation.