CORRELATED SQUEEZED-STATE APPROACH FOR THE GROUND-STATE OF STRONGLY CORRELATED ELECTRONS COUPLED TO LOCAL HOLSTEIN PHONONS

In the present work we have applied the correlated squeezed-state appr oach to investigate the ground state of the extended Hubbard model whi ch is coupled to local Holstein phonons. Our study begins with decoupl ing the electron and phonon subsystems approximately by introducing a variational correlated squeezed-state ansatz for the phonons. Then ass uming the renormalized intersite electron correlation of the effective electronic Hamiltonian to be attractive and the renormalized on-site correlation repulsive, we have applied the generalized Hartree-Fock ap proximation to obtain the ground state of the system, which is a super conducting state with intersite pairing. With optimal values of the va riational parameters the correlated squeezed-state approach will by co nstruction yield a ground-state energy lower than those obtained in pr evious studies. This means that our variational ansatz is more stable as the ground state of the system. Furthermore, our variational study shows that in the correlated squeezed state the polaronic reduction ef fect of phonons is much more alleviated, and thus the mass enhancement inherent to the polaron effect is noticeably weakened. This weakening of the reduction effect should, in turn, significantly affect other p hysical properties of the system.