mu SR studies of the flux vortex phases in a BEDT-TTF superconductor

mu SR has been used to probe the structure and stability of the flux vortex array in the organic superconductor kappa-(BEDT-TTF)(2)Cu(SCN)(2), At temp eratures below 5 K and fields below 5 mT the internal field distribution is found to closely match that expected for a three dimensional (3D) Abrikoso v flux line lattice (FLL). Careful studies in this 3D-FLL regime have enabl ed an improved measurement of the temperature dependence of the superconduc ting penetration depth to be made. A linear term is found in the temperatur e dependence of the penetration depth, suggesting the presence of line node s in the gap parameter and d-wave pairing.