Surface impedance studies on the electrodynamical response of organic superconductors

We have performed detailed measurements of the surface impedance in the normal and superconducting state of κ-(BEDT-TTF)2Cu(NCS)2 in the millimeter wave frequency range (1 cm−1 to 3 cm−1), and have evaluated the complex conductivity for different crystallographic orientations. Above the transition temperature, the material behaves like a metal with a scattering rate of approximately 20 cm−1. In the superconducting state the electrodynamics of both materials is in good agreement with calculations based on a BCS ground state: the penetration depth is temperature independent for T → 0; while the penetration depth and the coherence length are strongly anisotrop, the superconducting energy gap shows no indications of line nodes.