Josephson plasma resonance in κ-(BEDT-TTF)2Cu(NCS)2 for close to in-plane magnetic fields

We report detailed angle dependent Josephson plasma resonance measurements within the decoupled vortex liquid phase of the extreme two-dimensional organic superconductor κ-(BEDT-TTF) 2 Cu(NCS) 2 . The plasma resonance initially shows an approximately 1/cosθ dependence, followed by a sharp re-entrance for fields close to alignment with the layers (0 = 0°). This re-entrance may be attributed to an in-plane field dependence which may be directly related to the superconducting phase correlation function within the vortex state.