Size Effect of Nuclear Spin Relaxation Time in Superconducting Aluminum

Particles of aluminum having diameters less than 2000 {} were produced by evaporation in an argon atmosphere. The nuclear spin relaxation time was measured for three such samples in the normal and superconducting states between 0.36^∘{} and 1.3^∘{}K, for applied fields up to 400 G. In the normal state, and near Tc, the relaxation time is nearly the same as for bulk aluminum. Well below Tc the zero-field relaxation time is shorter than that of bulk aluminum, being less than one-fifth the bulk value at 0.4^∘{}K for two of the samples studied. At low temperatures there is also a field dependence which is characteristic of the superconducting state; T₁ increases with increasing field. At all fields, and low temperatures, the slope of a plot of lnT₁ versus TcT indicates a gap considerably smaller than the bulk value, but the limited temperature range covered makes such conclusions dubious.