Superconducting properties of tin-copper amorphous thin films

Abstract

The thermodynamic properties of the superconducting state in the amorphous Sn1−xCux thin films have been characterized. The concentration of copper changes in the range from 0.08 to 0.41. The calculations have been conducted in the framework of the strong-coupling formalism, wherein the Eliashberg functions determined in the tunnel experiment (Phys. Rev. B 51, 685 (1995)) have been used. The value of the Coulomb pseudopotential equal to 0.1 has been adopted. It has been found that the critical temperature (TC ) decreases from 7 K to 3.9 K. The ratio of the energy gap to the critical temperature: R∆ = 2∆ (0) /kBTC, differs significantly from the BCS value: R∆ ∈ 4.4, 3.95 . Similarly behaves the ratio of the specific heat jump to the specific heat of the normal state: RC = ∆C (TC ) /C N (TC ), and the parameter: RH = TC C N (TC ) /H 2 C (0), where HC (0) is the thermodynamic critical field. In particular, RC ∈ 2.2, 1.75 and RH ∈ 0.141, 0.154 .