We demonstrate spin injection into superconducting Nb by employing a spin absorption technique in lateral spin valve structures. Spin currents flowing in a nonmagnetic Cu channel are preferably absorbed into Nb due to its strong spin-orbit interaction, the amount of which dramatically changes below or above the superconducting critical temperature ($T_C$). The charge imbalance effect observed in the $\mathrm{Cu}/\mathrm{Nb}$ interface ensures that superconducting Nb absorbs pure spin currents even below $T_C$. Our analyses based on the density of states calculated using the Usadel equation can well reproduce the experimental results, implying that the strong spin-orbit interaction of Nb is still effective for the spin absorption even below $T_C$. Most importantly, our method allows us to determine the intrinsic spin relaxation time in the superconducting Nb, which reaches more than 4 times greater than that in the normal state.

• Received 8 October 2013

DOI:https://doi.org/10.1103/PhysRevLett.112.036602