Exact diagonalization study of the two-dimensionalt-Jmodel with adiabatic Holstein phonons: Single-hole case

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Abstract
We present exact results for the ground-state properties of the two-dimensional single-hole Peierls t-J model on finite square lattices, up to 18 effective sites in size. Using a Lanczos technique for unrestricted 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 wide 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 the local electron-phonon interaction increases, we find a self-trapping transition from a delocalized hole (polaronlike) state to a mainly localized 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 distortion and a quenched magnetic moment coupled ferromagnetically to an otherwise unperturbed AFM background. Aspects of the phase diagram are discussed.