MICROWAVE SURFACE IMPEDANCE OF KAPPA-(BEDT-TTF)2CU(NCS)2, WHERE BEDT-TTF IS BIS(ETHYLENEDITHIO)TETRATHIAFULVALENE - EVIDENCE FOR UNCONVENTIONAL SUPERCONDUCTIVITY

High-sensitivity microwave-impedance measurements performed on the qua si-two-dimensional organic superconductor kappa-(BEDT-TTF)2Cu(NCS)2 gi ve sound evidence for an unconventional type of superconductivity. The penetration depth lambda(T) is in excellent agreement with recent muo n-spin-relaxation measurements which are consistent with anisotropic p airings with lines of nodes in the energy pp. The real part of the con ductivity sigma1 shows a peaked structure which is free of coherence f actor effects and results from a competition between two temperature d ependences, the penetration depth and the inelastic relaxation time of the normal fluid.