Nuclear Spin-Lattice Relaxation in Superconducting Aluminum Alloys

The nuclear spin-lattice relaxation time, $T_1$, of superconducting aluminum alloys which contain up to 0.16% zinc or germanium has been measured in the range of 0.37°K to 1.2°K. A field cycling method was used. $T_1$ decreases slightly (less than 30%) with increasing-impurity concentration. The experimental data indicate that the anisotropy of the energy gap decreases with increasing reciprocal mean free path. The results are explained by means of the theory of dirty superconductors introduced by Anderson.