Superconductivity and the Very Strong Electron-Phonon Interaction in Amorphous Bi and Bi-Pb Alloys

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The temperature dependence of the electrical resistance R(T) and the upper critical field H_<c2>(T) have been measured in quench-condensed amorphous Bi and Bi-Pb alloys. The value of the electron-phonon interaction parameter λ was estimated based on the nearly free electron model and the strong coupling theory of superconductivity and turned out to be very large (λ〓1-3) in the amorphous state. The fact that the estimated λ-value is in good agreement with that estimated from tunnel effect measurements by Chen et al. and Knorr and Barth, verified that the nearly free electron model is fairly applicable to the amorphous phase. After an analysis based on the nearly free electron model and the BCS theory, some other physically important parameters, such as the mean free path l, the Fermi velocity v_F, the coherence length ζ_0, the London penetration depth λ_L(0), and the GL parameter κ, were also estimated.
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