Abstract
The transition curves of quenched lead films are measured in a perpendicular magnetic field as a function of the field strength. We vary the mean free path of the electrons by different condensation temperatures and by the annealing of the films. An influence of the edge of the film on the resistance measurement is suppressed by the superposition of iron onto the lead film. We will show, that the measured critical fieldB c ⊥ of the film is the upper critical fieldB c2 of a bulk superconductor with the sameeffective mean free path. As a result of the measurements we obtain ∂B c2/∂T as a function of the degree of disorder (the mean free path of the electrons) of the films. The results are compared with the theory of Gor'kov for the weak coupling superconductor and the theory of Eilenberger and Ambegaokar for the strong coupling superconductor. They disagree with both theories.
From the magnetic measurement we can determine the coherence length of lead. An independent determination at the same film is given by the proximity effect of the system Pb/Fe. The results of both methods are compared.
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We would like to thank Prof. Dr. R. Hilsch for his interest in this investigation. The experimental work was supported by the “Deutsche Forschungsgemeinschaft”.
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Koepke, R., Bergmann, G. The upper critical magnetic field of lead as a function of the mean free path of the electrons. Z. Physik 242, 31–44 (1971). https://doi.org/10.1007/BF01395377
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DOI: https://doi.org/10.1007/BF01395377