Variational Monte Carlo study of an interacting electron-phonon model

The phase diagram of a Hamiltonian with both on-site repulsion between electrons and with hopping probabilities which depend on dynamically varying separations of neighboring lattice sites has been studied with a new variational ansatz. A rich phase diagram is obtained as a function of density, electron-electron, and electron-phonon interaction strengths. The superconducting regime is characterized by a pattern of short and long bonds correlated with resonating pair hopping, whereas for the charge density wave phase this pattern is nearly static, and in the disordered and antiferromagnetic regimes all bond lengths are practically the same.