Experimental Investigation of Magnetic Field Dependence of Supercurrent in Multiply Connected Superconducting Films

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Abstract
Measurements of supercurrent density in thin films of tin have been made as a function of externally applied magnetic fields. Following the suggestion of Fulde and Ferrell, multiply connected sandwich-type samples of low self-inductance were prepared in order to observe the theoretically predicted gradual decrease of supercurrent due to depairing of superconducting pairs as the magnetic field is increased. Samples of low self-inductance are necessary to modify the normally observed first-order superconducting transition to a second-order one. Using samples of a suitable geometry, we have observed both total disappearance of supercurrent due to complete electron depairing in tin films and also the change from first to second order of the superconducting transition induced by an external magnetic field. Various experimental checks were made to verify that the decrease in supercurrent with increasing magnetic field was due to depairing and not spurious effects. The data have been analyzed to deduce supercurrent density versus the vector potential, the critical vector potential at which complete depairing takes place, the maximum current density, and their temperature dependences. The quantitative agreement between the experimental results and the predictions of the Ginzburg—Landau theory and its microscopic extensions is reasonably good.