2013/06/27 by Manfred Bucher, Bucher, Manfred
Physics and Astronomy · #FOS: Physical sciences #General Physics (physics.gen-ph) #physics.gen-ph
paper · pdf · doi:10.48550/arxiv.1306.6405
37 pages, 20 figures. Same as version 1, but with better scale-labeling in Fig. 11
arxiv created 2013/06/28 · arxiv updated 2013/07/01
Emergence, development and cessation of superconductivity in three representative compounds of copper oxide families---cation doped Ca2-xNaxCuO2Cl2 and La2-xAexCuO4 (Ae = Ba, Sr), as well as oxygen enriched YBa2Cu3O6+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 O2- 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 Ca2-xNaxCuO2Cl2, 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 La2-xAexCuO4 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 YBa2Cu3O6+x indirectly leads to effective doping in the CuO2 planes themselves (Cu2+ --> Cu3+). The ionization of copper ions at the corners of planar unit cells determines whether lateral oscillations between next-nearest neighbor O2- 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.