${}_{}{}^9{}_{}{}^{}\mathrm{Be}$ NMR and relaxation have been used to probe heavy-fermion superconductivity in ${\mathrm{U}}_{1-x}{\mathrm{Th}}_x{\mathrm{Be}}_{13}$, $x=0\mathrm{} \mathrm{and} 0.033$. The spin-lattice relaxation rate $\frac{1}{T_1}$ varies approximately as $T^3$ well below the transition temperature. This is consistent with a class of anisotropic pairing models for which the gap vanishes along lines on the Fermi surface. NMR spectra give no indication of magnetic, structural, or charge-density ordering at a second transition for $x=0.033\mathrm{}$.

• Received 10 August 1984

DOI:https://doi.org/10.1103/PhysRevLett.53.1833