Nature of the charge carriers and their pairing state in the anisotropic three-dimensional lightly doped cuprates

Abstract

The self-trapping and pairing of carriers in the three-dimensional (3D) isotropic and anisotropic high-Tc cuprates are studied in the strong electron–phonon coupling limit. It is shown that the relevant charge carriers in these systems are large (bi)polarons. The ground-state energies of large polarons and bipolarons in the doped cuprates are calculated variationally as a function of the ratio of the optic to the static dielectric constant η=ε∞/ε0, taking into account the short- and long-range electron–phonon interactions and Coulomb correlation in the continuum model and adiabatic approximation. It is found that the formation of a large acousto-optic bipolaron is possible in a broad region of η.