authors: M. Capone,
G. Sangiovanni ,
C. Castellani, C. Di
Castro, and M. Grilli
The single-band Hubbard-Holstein model represents the simplest model realization of strongly correlated electrons interacting with phonon modes. This model has been proposed to be relevant for a number of important compounds, like the high temperature superconductors. We focus on the possibility of charge instabilities like phase separation or charge-density waves in the strongly correlated regime close to the Mott insulating state. In the framework of Dynamical Mean Field Theory we study the competition between the metallic and the insulating phase as a function of the density and of the electron-phonon coupling, in the intermediate-large Hubbard U regime. We show that a region in which the system is unstable towards phase separation exists for densities close to half-filling for intermediate electron-phonon coupling. The size of the phase separation region grows with the coupling, and the instability always occurs before reaching the polaronic regime.