Coulomb-oscillator origin of superconductivity in p-doped copper oxides

Abstract

Emergence, development and cessation of superconductivity in three representative compounds of copper oxide families---cation doped Ca_2-xNa_xCuO2Cl2 and La_2-xAe_xCuO4 (Ae = Ba, Sr), as well as oxygen enriched YBa2Cu3O_6+x ---are explained with the Coulomb-oscillator model of superconductivity. By the model, non-resistive current is carried by axial Coulomb oscillations of s electrons through neighbor nuclei---here excited 3s electrons from O^2- ions through next-nearest neighbor oxygen nuclei---if their accompanying lateral oscillation is sufficiently confined to prevent lateral overswing. Cation doping gives rise to a superlattice in the layers that sandwich each CuO2 plane. In Ca_2-xNa_xCuO2Cl2, having one CuO2 plane per unit cell, superconductivity emerges when laterally confined Coulomb oscillators start connecting along 6 x 6 superlattice domains (in units of planar lattice constants) and it peaks at 4 x 4 domains when, at doping x = 1/8, the superlattice is completed. With further doping a new, off-set superlattice grows. Its frustrating effect gradually reduces superconductivity to cessation. The same mechanism holds for La_2-xAe_xCuO4 which has two, staggered CuO2 planes per unit cell. The staggering causes superconducting frustration or boost between adjacent layer sandwiches. This results in a double hump of the transition temperature Tc(x), instead of a dome, with a deep furrow or dip at x = 1/8 for Ae = Ba or Sr, respectively. Oxygen enrichment of YBa2Cu3O_6+x indirectly leads to effective doping in the CuO2 planes themselves (Cu^2+ --> Cu^3+). The ionization of copper ions at the corners of planar unit cells determines whether lateral oscillations between next-nearest neighbor O^2- ions overswing (Tc = 0) or are confined to wide or narrow electron tracks. Their percolating connectivity gives rise to respective plateaus of Tc = 57 K and Tc = 90 K, and intermediate ramps.