Phase transition of thin-film superconducting cylinders in a magnetic field. I. Parallel-field measurements

The superconducting transition temperature was measured as a function of magnetic field for thin-film hollow cylinders in an accurately parallel magnetic field. Quantitative results were obtained for one indium and nine aluminum cylinders with film thicknesses d varying from 2900 to 340 Å and with diameters from 1.4 to 4.8 μ. The results agree well with Tinkham's analysis based on the Ginzburg–Landau theory even in the very-thin-film region where the penetration depth λ≫d and the transition region is greatly broadened. Values of λ obtained from the amplitude of periodic variations of T_c with H and from the background monotonic variation of T_c both agree with values derived from the low-temperature critical field and theoretical estimates. A search for higher-order electron correlations which would give an admixture of higher periodicity of flux quantization yielded a negative result. Evidence was found for the effect of fluctuations on the magnetic field dependence of the phase boundary.