Theory of High-Tc Superconductivity: Transition Temperature

Abstract: It is demonstrated that the transition temperature (Tc) of high-Tc 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-Tc materials (cuprates, ruthenates, rutheno-cuprates, iron pnictides, organics) yields the universal relationship for optimal compounds, kBTc0 = {\beta}/\ell{\zeta}, where \ell is related to the mean spacing between interacting charges in the layers, {\zeta} is the distance between interacting electronic layers, {\beta} is a universal constant and Tc0 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 Tc < Tc0. It is shown that Tc0 may be obtained from an average of Coulomb interaction forces between the two layers.