Precursor non-superconducting pairing and novel superconductivity in underdoped and optimally doped cuprates

The precursor non-superconducting pairing of carriers and the novel superconductivity in high-Tc cuprates are studied within the large (bi)polaron model and the new BCS-like fermion and boson mean-field approximations by treating a two-component charge carrier picture. It is argued that pre-formed pairs (large bipolarons) reside in underdoped cuprates between the CuO2 planes and remain localized in the z-direction. With lowering temperature, these large bipolarons condense into a superfluid quasi-one-dimensional Bose-liquid state. In the intermediate electron-phonon coupling regime, the Cooper-pair formation and condensation in the CuO2 layers occur also at different temperatures. Large bipolarons and polaron Cooper pairs in optimally doped cuprates condense into a superfluid Bose-liquid state almost at the same temperature due to the doping-induced dimensional crossover