The Influence of Electron Transfer on T c in Superconductors

Abstract

Increase of T c in Al 1 − x (SiO 2 ) x cermets with increasing x is caused by electron transfer from the Al grains to the SiO 2 phase occupying surface states, expressed by T c / T c , max = 1 − γ ⋅ n 2 (*), where n is the electron density in the Al phase and γ a characteristic parameter. Decrease of T c in Pb-Cu-sandwiches is attributed to the electron transfer from the Cu film to the Pb film. γ and T c , max in equation (*) stands for the influence of the electron-phonon interaction and n 2 for the influence of the electron-electron Coulomb repulsion on T c . The result that equation (*) holds for both hole-doped cuprate high-temperature superconductivity (HTSC) and Al 1 − x (SiO 2 ) x cermets is an important indication that common mechanisms underlie HTSC and classical superconductors. The difference between the two is that in HTSC, electron transfer occurs between different electronic bands, but in Al 1 − x (SiO 2 ) x cermets between different phases.