Electrodynamics of the organic superconductors κ-(BEDT-TTF)2Cu(NCS)2 and κ-(BEDT-TTF)2Cu[N(CN)2]Br

Abstract

We have performed measurements of the surface impedance in the normal and superconducting states of the title compounds in the millimeter wave-frequency range (1–3 cm-1), and have evaluated the complex conductivity for different crystallographic orientations. Above the transition temperature, the materials behave like metals with a scattering rate of approximately 20 cm-1. In the superconducting state the electrodynamics is in good agreement with calculations based on a BCS ground state: while the penetration depth and the coherence length are anisotropic, the superconducting energy gap shows no indications of line nodes.