THE PHASE-DIAGRAM OF THE 2D HOLSTEIN-T-J MODEL NEAR HALF FILLING

We have used an exact diagonalization technique to explore the ground-state phase diagram of the two-dimensional Holstein-t-J model near half filling. The nature of the ground state is analysed. calculating self consistently the local lattice distortions, on-site spin and charge densities, as well as the magnetic structure form factor. We demonstrate that doped holes tend to form hole-polaron or bipolaron states. Compared to that in the uncorrelated model (spinless fermions), the critical electron-phonon coupling strength for the self-trapping transition of the doped charge carriers is considerably reduced by the antiferromagrietic exchange interaction. The relevance to the cuprate superconductors is discussed.