Nuclear Magnetic Resonance in Superconducting Tin

The nuclear magnetic resonance (NMR) is investigated in small particles ({~}100 A diam) of β tin between 1.5 and 4.2^∘{}K, and in magnetic fields between 1.2 and 8.8 kilogauss. The critical temperature and critical field are 3.71^∘{}K and 25 kilogauss, respectively. The effective penetration depth for the superconducting particles is estimated to be 1500 A. The resonance linewidth is 0.34% of the magnetic field, and it is independent of temperature. With respect to α tin, the NMR shift for β tin is 0.77% in the normal state; it approaches 0.59% in the superconductor as T→0. (The largest known chemical shift is only 0.17%.) The variation with magnetic field is less than 0.03%. One may conclude that the electronic spin susceptibility in the superconducting particles at absolute zero is approximately three quarters of the normal value. The result for 1000 A particles, though less accurate, is substantially the same.