The density-driven Mott transition is studied by means of dynamical mean-field theory in the Hubbard-Holstein model, where the Hubbard term leading to the Mott transition is supplemented by an electron-phonon ($e$-ph) term. We show that an intermediate $e$-ph coupling leads to a first-order transition at $T=0$, which is accompanied by a phase separation between a metal and an insulator. The compressibility in the metallic phase is substantially enhanced. At quite larger values of the coupling, a polaronic phase emerges coexisting with a nonpolaronic metal.

• Received 30 May 2003

DOI:https://doi.org/10.1103/PhysRevLett.92.106401