Size effect of nuclear spin relaxation time in superconducting aluminum

Particles of aluminum having diameters less than 2000 Ã 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. © 1964 The American Physical Society.