Abstract
The magnetic field penetration depth λ of superconductors has been measured in the past by various radiofrequency and microwave techniques or by using small colloidal samples. In this paper we describe a new method, which we have successfully applied to tin, for directly measuring the temperature dependence of λ at dc and on macroscopic, oriented single crystals. The method utilizes the extremely high flux sensitivity of a SQUID magnetometer to measure the flux penetrating into a superconductor in a low (~ 1 Oe) static magnetic field. With this technique changes in λ as small as 2 A can be resolved. Moreover, flat, planar samples have been used so that both the direction of the shielding current J and the normal \(\hat{n}\) to the sample surface can be directed along well-defined crystallographic directions. The temperature dependence of λ is found to depend on both Ĵ and \(\hat{n}\). While a dependence on Ĵ has been observed previously, the dependence on \(\hat{n}\) has not. As described below, both types of anisotropy can be understood on the basis of Pippard’s nonlocal theory1 of electrodynamics.
Published Version
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