Superconducting properties of tin-copper amorphous thin films

Abstract

The thermodynamic properties of the superconducting state in the amorphous $\mathrm{S}{\mathrm{n}}_{1-\mathrm{x}}\mathrm{C}{\mathrm{u}}_{\mathrm{x}}$ 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 {\bf 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 ($T_C$) decreases from $7$ K to $3.9$ K. The ratio of the energy gap to the critical temperature: $R_{\Delta }=2\Delta \left(0\right)/k_B{T}_C$, differs significantly from the BCS value: $R_{\Delta }\in ⟨4.4,3.95⟩$. Similarly behaves the ratio of the specific heat jump to the specific heat of the normal state: $R_C=\Delta C\left(T_C\right)/C^N\left(T_C\right)$, and the parameter: $R_H=T_C{C}^N\left(T_C\right)/H_C^2\left(0\right)$, where $H_C\left(0\right)$ is the thermodynamic critical field. In particular, $R_C\in ⟨2.2,1.75⟩$ and $R_H\in ⟨0.141,0.154⟩$.