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

TL;DR

This paper explains the emergence and cessation of superconductivity in copper oxides using the Coulomb-oscillator model, emphasizing how electron oscillations and superlattice structures influence critical temperatures.

Contribution

It introduces a Coulomb-oscillator based explanation for superconductivity in copper oxides, linking doping-induced superlattices to electron oscillation confinement and Tc variations.

Findings

Superconductivity peaks at specific superlattice domain sizes.

Doping levels correlate with superlattice formation and Tc changes.

Oxygen enrichment affects copper ionization, influencing electron oscillation confinement.

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.