Studies of the microwave resistivity of κ-(BEDT-TTF)2Cu[N(CN)2]Cl

We have performed temperature dependent measurements of the surface impedance of κ-(BEDT-TTF)2Cu[N(CN)2]Cl in both directions, parallel and perpendicular to the highly conducting planes. In both orientations the microwave resistivity basically follows the dc behavior for T > 15 K: the crystal undergoes a broad metal-insulator transition at around 50 K. While there are no indications of superconductivity at ambient pressure found in the dc resistivity and by ac susceptibility, the microwave resistivity clearly drops at 13 K and again at 5 K, indicating two superconducting phases. When pressure is applied by embedding it in grease, only the well known superconducting phase transition at Tc = 13 K remains.