Fluxoid Quantization and Field-Induced Depairing in a Hollow Superconducting Microcylinder

Abstract

Little and Parks demonstrated that the superconducting transition temperature ${T}_{c}$ of a multiply connected superconductor is periodic in a magnetic field with a periodicity of $\frac{\mathrm{hc}}{2e}$. However, there were certain anomalous features of the early experiments, such as an unexplained temperature dependence of the amplitude of the $\ensuremath{\Delta}{T}_{c}$ oscillations and an unexplained nonoscillatory magnetic field background superposed on the oscillatory field dependence of ${T}_{c}$. By repeating the experiment under more controlled conditions, we have eliminated the problems which led to the anomalous features of the early results. Isothermal resistance-versus-magnetic-field measurements were made on Sn and Al cylinders of various diameters in the range 1-5 \ensuremath{\mu}. From these measurements detailed phase diagrams (${T}_{c}$-versus-$H$ curves) were constructed which are in excellent agreement with the predictions of the linearized Ginzburg-Landau theory. The present type of experiment is shown to be suitable for studying depairing due to kinetic-energy effects associated with the drift motion of Cooper pairs. The results are discussed within the framework of the pairbreaking theory of Abrikosov and Gor'kov, which has been adapted to treat the present problem.