Penetration of Magnetic Field into Superconducting Mercury

Abstract

IT is well known that a magnetic field is almost completely excluded from a superconductor, so that a long cylinder has a diamagnetic susceptibility which is 1/4 for a field parallel to the cylinder axis, or 1/2 for a transverse field. The magnetic field does, however, penetrate slightly, so that the actual diamagnetic susceptibility should be slightly smaller than X₀, and elementary considerations show that we should have where defines a penetration depth and r is the cylinder radius. Previous experiments by one of us¹ on colloidal mercury, and by Appleyard and others² on thin mercury films (in both cases involving specimen size comparable to or smaller than ), showed that is of the order of 10^-5 cm. and increases several times as the temperature approaches the transition point (4.17° K.). Thus for cylinders with radii of order 10^-3 cm. should vary by a few percent close to 4.17° K.