HOLE DYNAMICS IN DOPED CUPRATES - HIGH-T-C SUPERCONDUCTIVITY ORIGINATED FROM ANTIFERROMAGNETIC EXCHANGE AS A DIRECT ATTRACTIVE INTERACTION

A strong-coupling-limit theory of hole dynamics in copper oxide superc onductors is developed. The theory is based on the t-t'-J model and th e diagrammatic technique for projection operators. For the normal stat e two different phases at finite temperature are found. For the first (which is realized at low doping), a Fermi surface (FS) is formed by d oped holes only and so has a volume proportional to delta, while d ele ctrons are responsible for a localized magnetism. For the second (whic h is realized at intermediate doping), the d electrons become a part o f the FS the volume of which is proportional to 1 + delta, while the s ystem loses the magnetic moments associated with d electrons. A transi tion between the two phases is of first order and the FS changes abrup tly from a small to a large one. The phase with the small FS is unstab le when lowering the temperature in as much as a spin susceptibility d iverges at k = Q(AF). Therefore, at low temperature within the doping range corresponding to this phase, a long-range antiferromagnetic (AF) ground state or quantum-disordered ground state is realized depending on doping. Most attention in the paper is paid to the second state ch aracterized by a saddlepoint (SP) singularity and a large Fermi surfac e. Self-consistent calculations for the chemical potential show that a t some critical doping which depends on the ratio of hopping parameter s t'/t, the Fermi level crosses the SP. For this phase, a short-distan ce superconducting (SC) pairing of d-wave symmetry with a large amplit ude of the SC gap is found at low temperature. The critical temperatur e is very high. The superconducting pairing has a magnetic origin but the mechanism is different from an exchange by spin waves. The mechani sm is related to the AF exchange between localized spins, turning out to be a direct attractive interaction between carriers. The latter poi nt is a consequence of the specific nature of carriers appearing as a result of strong on-site Coulomb repulsion. On the other hand, the spe cific kinematic properties of the carriers create a strong constraint on symmetry of the superconducting order parameter which eliminates al l symmetries without nodes and favors strongly d-wave symmetry. In suc h a situation the existence of a saddle point close to the Fermi level is a factor providing a maximum value of the effective interaction. A n interrelation between an extension of the SP singularity and a value of the amplitude of the SC gap is analyzed; a saturation effect is fo und.