High and Ultra High Magnetic Field Studies of Newly Synthesized OrganicSuperconductors

摘要

To understand the nature of the superconducting state, we studied the new organicsuperconductor (BETS)2GaCl4, that was synthesized by our collaborator L. K. Montgomery. The BETS donor molecule is a variant of the BEDT molecule where four of the inner sulfur atoms are replaced with selenium atoms. The larger selenium atoms produce a larger overlap of the orbitals in the conducting sheets of the crystals and hence produce wider electronic bands. We used RF penetration depth measurements at 24 MHz initially to map out the H sub c2 diagram of (BETS)2GaCl4. The measurements were much more successful than we expected yielding many details about the superconducting state and the vortex lattice. As an example, we were able to measure the pinning force potential, often called the Labush parameter, as a function of temperature from 100 mK to 4.5 K. Knowing this parameter enabled us to calculate a critical current at zero temperature of 2 x 10(exp 4) A/sq cm for this material.