Theory of high-TC superconductivity: transition temperature

It is demonstrated that the transition temperature (T-C) of high-T-C superconductors is determined by their layered crystal structure, bond lengths, valency properties of the ions, and Coulomb coupling between electronic bands in adjacent, spatially separated layers. Analysis of 31 high-T-C materials (cuprates, ruthenates, ruthenocuprates, iron pnictides, organics) yields the universal relationship for optimal compounds, k(B)T(C0) = beta/l zeta, where l is related to the mean spacing between interacting charges in the layers,. is the distance between interacting electronic layers, beta is a universal constant and T-C0 is the optimal transition temperature (determined to within an uncertainty of +/- 1.4 K by this relationship). Non-optimum compounds, in which sample degradation is evident, e. g. by broadened superconducting transitions and diminished Meissner fractions, typically exhibit reduced T-C < T-C0. It is shown that T-C0 may be obtained from an average of the Coulomb interaction forces between the two layers.