NMR RELAXATION RATE IN THE SUPERCONDUCTING STATE OF THE ORGANIC CONDUCTOR KAPPA-(BEDT-TTF)(2)CU[N(CN)(2)]BR

The C-13 nuclear spin-lattice relaxation rate, T-13(1)-1 has been meas ured in the superconducting state of kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br in a field parallel to the conducting layers. The T-13(1)-1 exhibits an abrupt decrease just below the transition temperature without any i ndication of the Hebel-Slichter coherence peak. By separation of the v ortex-dynamics contribution to T-13(1)-1 with the use of H-1-NMR, the quasiparticle contribution to T-13(1)-1 is found to follow a T-3 law t hat is consistent with unconventional superconductivity with line node s in gap parameter on the Fermi surface or highly anisotropic supercon ductivity.