Superconducting effective-mass anisotropy in κ-(BEDT- TTF)2Cu(NCS)2[where BEDT-TTF is bis(ethylenedithio)tetra- thiafulvalene]

We have performed a torque magnetometry study of an organic superconductor. The results indicate that the superconductivity of κ-BEDT-${\mathrm{TTF}}_2$Cu(NCS${)}_2$ is extremely anisotropic, and suggest a lower bound of 4×${10}^4$ for the superconducting effective-mass anisotropy. Our data have also allowed us to make a detailed test of the predictions of the three-dimensional (3D) model for the torque and also those of a recently suggested ‘‘2D’’ approach. Our results are in better agreement with the predictions of the 3D model.