Superconductivity in aligned laminar composites

Abstract

Long ribbons of oriented lamellar superconductor-normal composites have been prepared by a high-speed directional solidification technique. Typically the samples are composed of 5000 alternating superconducting and normal-metal layers in which the pair potential is modulated with an amplitude of half the bulk superconductor pair potential value. By controlling the growth rate, the period of modulation can be selected to be any value in the range 5000-90000 Å. Studies of flux pinning and flux flow are reported for transport currents both parallel and perpendicular to the layers. For vortex motion parallel to the layers, flux enters the normal-metal region of the specimen and moves across the specimen at current densities on the order of 100 A/${\mathrm{cm}}^2$. For vortex motion perpendicular to the layers, there is no flux flow until current densities are on the order of 50000 A/${\mathrm{cm}}^2$. Hence, the anisotropy in critical current is approximately a factor of 500.