Backflow Effect on Spin Diffusion at the Normal Metal-Superconductor Interface

The behavior of spin propagation in metals in various measurement schemes is shown to be qualitatively different than a simple exponential decay - due to the backflow effect on spin diffusion in the presence of interfaces. We utilize the spin sensitivity of Nb superconducting point contacts to evaluate the spin current depolarization in a normal metal. The spin current was injected from bulk Co₂Mn_0:5Fe_0:5Si Heusler alloys into gold films of variable thickness. While our phenomenological theoretical results are consistent with gradually decaying spin polarization as the film thickness increases, the spin diffusion length in Au is found to be 285 nm, more than two times larger than without taking the backflow effect into account.