Electrodynamics of the superconducting state of κ(BEDT-TTF)2Cu(NCS)2

We have measured the surface impedance ${\mathit{Z}}_{\mathit{s}}$=${\mathit{R}}_{\mathit{s}}$+${\mathit{iX}}_{\mathit{s}}$ in the normal and superconducting states of κ(BEDT-TTF${)}_2$Cu(NCS${)}_2$, and have evaluated the conductivity ${\mathrm{\sigma }}_1$. The temperature-independent ${\mathit{X}}_{\mathit{s}}$ for T≪${\mathit{T}}_{\mathit{c}}$ and the weak maximum observed for ${\mathrm{\sigma }}_1$ below ${\mathit{T}}_{\mathit{c}}$ rule out unusual pairing. Our results are in good overall agreement with calculations based on a BCS ground state.