Hole-polarons and bipolarons in the Holstein t − J model: Relevance of inter-site hole-phonon interaction

Abstract

The interaction of the doped holes with lattice vibrations in an antiferromagnetic (AF) background is studied using the t−J-Holstein model on an 8-site cluster with 2-holes by an exact method. The phonon mediated interactions between the holes at nearest-neighbor (NN) sites are considered. We have calculated the effective kinetic energy, hole-phonon and hole–hole correlations, two hole binding energy to study the nature and stability of various quasiparticles. At negligible to very weak hole-phonon (h−ph) couplings, the holes get dressed by the AF background forming spin-polarons. At weak to intermediate h−ph couplings, the holes are dressed by the phonon cloud forming large hole-polarons and/or nearly free hole-polarons. A narrow transition region is observed at intermediate h−ph coupling depending on phonon energy, which marks the formation of S1 hole-bipolarons and small-hole-polarons. At strong coupling regime, stable hole-bipolarons are formed which may lead to superconducting condensation. We also argue that these results cannot be completely reproduced by considering pure attraction between holes. Results show the relevance of inter-site h−ph coupling in high Tc cuprates.