Polaronic effects in strongly coupled electron-phonon systems: Exact diagonalization results for the 2D Holstein t–J model

Ground–state and dynamical properties of the 2D Holstein t–J model are examined by means of direct Lanczos diagonalization, using a truncation method of the phononic Hilbert space. The single– hole spectral function shows the formation of a narrow hole–polaron band as the electron–phonon coupling increases, where the polaronic band collapse is favoured by strong Coulomb correlations. In the two–hole sector, the hole–hole correlations unambiguously indicate the existence of inter–site bipolaronic states. At quarter–filling, a polaronic superlattice is formed in the adiabatic strong–coupling regime.