Nuclear Spin-Lattice Relaxation in Superconducting Aluminum

Abstract

The nuclear spin-lattice relaxation time of superconducting aluminum has been measured from 0.35°K to the critical temperature. The method used was that of Hebel and Slichter; low temperatures were attained through the use of a helium-three cryostat. The estimated energy gap is $3.2 k{T}_c$, in agreement with microwave measurements. The data are in good agreement with the predictions of Hebel and Slichter based on the Bardeen, Cooper, and Schrieffer theory of superconductivity. The data indicate a smearing or width of the BCS energy levels which decreases with increasing temperature and is approximately $\frac{1}{10}$ of the energy gap at all temperatures.