Superconducting effective-mass anisotropy in kappa -(BEDT- TTF)2 Cu(NCS)2

We have performed a torque magnetometry study of an organic superconductor. The results indicate that the superconductivity of \ensuremath{\kappa}-BEDT-${\mathrm{TTF}}_{2}$Cu(NCS${)}_{2}$ is extremely anisotropic, and suggest a lower bound of 4\ifmmode\times\else\texttimes\fi{}${10}^{4}$ 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.