Low-field cross spin relaxation of L8 i in superconducting NbSe2

A low energy beam of spin polarized L8 i has been used to investigate nuclear spin relaxation in the multiband superconductor NbSe2. In low magnetic fields there is significant cross relaxation between the L8 i and the host N 93 b spins, which is driven by low frequency fluctuations in the nuclear magnetic dipolar interaction. The rate of cross relaxation is strongly field dependent and thus the 1/ T1 spin relaxation rate of the L8 i is a sensitive monitor of the static local magnetic field B just below the surface. This in turn is used to determine the absolute value of the magnetic penetration depth λ in the Meissner state. The temperature variations in 1/ T1 and λ are consistent with a wide distribution of superconducting gaps expected for a multiband superconductor.