Phase Transition of Thin-Film Superconducting Cylinders in a Magnetic Field. II. Angular Dependence

The normal-superconducting phase boundary for a thin-film microcylinder was measured in a magnetic field $\overrightarrow{\mathrm{H}}$ making an angle $\theta$ with the cylinder's axis. The depression of the transition temperature for small values of transverse field $H_t$ was proportional to $H_t^2$ as predicted by Tinkham, and equaled the predicted magnitude. At larger values of $H_t$ there was a sudden discontinuity of slope in the $T_c$-vs-$H^2$ curve at a critical value of the transverse field $H_{\mathrm{tc}}$. This discontinuity in slope apparently corresponds to a change from a superconducting state with uniform field penetration in the transverse direction to one with a single row of transverse vortices, the transverse-angular-momentum quantum number of the carriers changing from 0 to 1. A peculiar splitting of the flux-quantization resistance maxima was observed in the neighborhood of $H_{\mathrm{tc}}$ and qualitatively explained.