Affiliation: | a Department of Physics and The Science and Technology Center for Superconductivity, University of Illinois at Urbana-Champaign, 1110 W. Green, Urbana, IL 61801, USA b Chemistry and Materials Science Division, Argonne National Laboratory, Argonne, IL 60439, USA |
Abstract: | The magnetic field dependence of the in-plane penetration depth λ|(H) for single crystal κ-(ET)2Cu[N(CN)2]Br has been measured at 3, 9.6, and 36 MHz. Over a limited range, λ| scales with a characteristic field H*(T) that coincides with a shoulder in the λ| vs. H curves. Above that field, λ| increases sharply toward a second inflection point at H**(T) that coincides with is close to the irreversibility line measured by magnetization. For fields larger than H** the penetration depth diverges, suggesting that the vortex lattice has melted. The field dependence at one frequency agrees qualitatively with a model of pinned vortices at low fields giving way to flux flow at higher fields. However, the observed frequency dependence deviates significantly from the predictions of this model, suggesting that collective effects play a major role. Our technique also yields a new measurement for the interplane penetration depth λ 300 μm, implying an anisotropy λ/λ| > 200. |