We study spin transport in a superconducting nanowire using a set of closely spaced magnetic tunnel contacts. We observe a giant enhancement of the spin accumulation of up to 5 orders of magnitude on transition into the superconducting state, consistent with the expected changes in the density of states. The spin relaxation length decreases by an order of magnitude from its value in the normal state. These measurements, combined with our theoretical model, allow us to distinguish the individual spin-flip mechanisms present in the transport channel. Our conclusion is that magnetic impurities rather than spin-orbit coupling dominate spin-flip scattering in the superconducting state.

Non-local measurements are performed on a multi terminal device to in − situ determine the spin diffusion length and in combination with resistivity measurements also the spin relaxation time in Al films. By varying the thickness of Al we determine the contribution to spin relaxation from surface scattering. From the temperature dependence of the spin diffusion length it is established that the spin relaxation is impurity dominated at low temperature. A comparison of the spin and momentum relaxation lengths for different thicknesses reveals that the spin flip scattering at the surfaces is weak compared to that within the bulk of the Al films. PACS numbers:The first experiment on spin injection and detection in metals dates back to 1985 when Johnson and Silsbee [1,2] demonstrated spin accumulation in a single-crystal Al for temperatures below 77 K, with a spin diffusion length, λ sf ∼ 100 µm. Recent experiments on thin films [3,4,5,6,15] found orders of magnitude shorter λ sf ∼ 0.1 − 1 µm. However, the measured spin accumulation is greatly enhanced due to much reduced effective device volumes. Understanding the origins of spin relaxation in such devices is therefore important for spintronics applications. The main contribution to spin relaxation in a metal is the spin * Electronic address: poli@kth.se

The notion of decoupling of spin and charge currents is one of the basic principles underlying the rapidly expanding field of spintronics. However, no direct demonstration of the phenomenon exists. We report a novel measurement in which a nonequilibrium spin population is created by a pointlike injection of current from a ferromagnet across a tunnel barrier into a one-dimensional spin channel and detected differentially by a pair of ferromagnetic electrodes placed symmetrically about the injection point. We demonstrate that the spin current is strictly isotropic about the injection point and, therefore, completely decoupled from the unidirectional charge current.

A lateral array of ferromagnetic tunnel junctions is used to inject and detect non-equilibrium quasi-particle spin distribution in a superconducting strip made of Al. The strip width and thickness is kept below the quasi particle spin diffusion length in Al. Non-local measurements in multiple parallel and antiparallel magnetic states of the detectors are used to in-situ determine the quasi-particle spin diffusion length. A very large increase in the spin accumulation in the superconducting state compared to that in the normal state is observed and is attributed to a diminishing of the quasi-particle population by opening of the gap below the transition temperature.Comment: 6 pages, 4 figures; accepted for publication in Journal of Applied Physic