Spin Injection into Superconductor with Strong Spin-Orbit Coupling

Orateur : Taro WAKAMURA (University of Tokyo, Otani's group)

We report on spin injection into superconducting Nb by employing spin absorption technique in the lateral spin valve structures [1]. Spin currents flowing in nonmagnetic Cu channel are preferably absorbed into Nb due to its strong spin-orbit (SO) interaction. The amount of spin absorption strongly depends on the spin injection current I between Py (Ni81Fe19) and Cu only below TC (=5.5 K) . The charge imbalance effect observed in the Cu/Nb interface assures that superconducting Nb absorbs pure spin currents even below TC [2]. Our analyses based on the density of states calculated using the Usadel equation can well reproduce the experimental results, implying that the strong SO interaction of Nb is still effective for the spin absorption even below TC. Most importantly our method allows us to determine the intrinsic spin relaxation time (sf) in the superconducting Nb [3], which reaches by more than four times greater than that in the normal state. By employing our device structure and calculation method, we can evaluate sf free from the effects which made previous experimental results inconsistent each other [4]. References 1. Y. Niimi et al., Phys. Rev. Lett. 109, 156602 (2012). 2. P. Cadden-Zimansky and V. Chandrasekhar, Phys. Rev. Lett. 97, 237003 (2006). 3. T. Wakamura et al., Phys. Rev. Lett. 112, 036602 (2014). 4. H. Yang et al., Nat. Mater. 9, 586 (2010), Y-S. Shun et al., Phys. Rev. B 71, 144513(2005), C. D. Chen et al., Phys. Rev. Lett. 88, 047004 (2002).

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