Paramagnetic limiting of the upper critical field of the layered organic superconductor kappa-(BEDT-TTF)(2)Cu(SCN)(2)

We report detailed measurements of the interlayer magnetoresistance of the layered organic superconductor kappa-(BEDT-TTF)(2)Cu(SCN)(2) for temperatur es down to 0.5 K and fields up to 30 T. The upper critical field is determi ned from the resistive transition for a wide range of temperatures and fiel d directions. For magnetic fields parallel to the layers, the upper critica l field increases approximately linearly with decreasing temperature. The u pper critical field at low temperatures is compared to the Pauli paramagnet ic limit, at which singlet superconductivity should be destroyed by the Zee man splitting of the electron spins. The measured value is comparable to a value for the paramagnetic limit calculated from thermodynamic quantities b ut exceeds the limit calculated from BCS theory. The angular dependence of the upper critical field shows a cusplike feature for fields close to the l ayers, consistent with decoupled layers.