EXACT DIAGONALIZATION STUDY OF THE 2-DIMENSIONAL T-J MODEL WITH ADIABATIC HOLSTEIN PHONONS - SINGLE-HOLE CASE

We present exact results for the ground-state properties of the two-di mensional single-hole Peierls t-J model on finite square lattices, up to 18 effective sites in size. Using a Lanczos technique for unrestric ted energy minimization with respect to local lattice distortions, we study the competition between intrasite electron-phonon and intersite antiferromagnetic (AFM) exchange coupling on the hole state over a wid e range of interaction strengths. The structure of the doping state is examined by calculating local expectation values of spin and electron densities as well as magnetic and charge correlation functions. As th e local electron-phonon interaction increases, we find a self-trapping transition from a delocalized hole (polaronlike) state to a mainly lo calized hole state. Despite a weak lattice distortion the delocalized case has similar properties to the ground state of the pure t-J model, whereas the localized hole state exhibits strong local lattice distor tion and a quenched magnetic moment coupled ferromagnetically to an ot herwise unperturbed AFM background. Aspects of the phase diagram are d iscussed.