Department of Physics, NTNU, Norwegian University of Science and Technology, N-7491, Trondheim, Norway.
Department of Materials Science, University of Cambridge, Cambridge, CB3 0FS, United Kingdom.
Sci Rep. 2017 May 16;7(1):1932. doi: 10.1038/s41598-017-01330-1.
Interfacing superconductors with strongly spin-polarized magnetic materials opens the possibility to discover new spintronic devices in which spin-triplet Cooper pairs play a key role. Motivated by the recent derivation of spin-polarized quasiclassical boundary conditions capable of describing such a scenario in the diffusive limit, we consider the emergent physics in hybrid structures comprised of a conventional s-wave superconductor (e.g. Nb, Al) and either strongly spin-polarized ferromagnetic insulators (e.g. EuO, GdN) or halfmetallic ferromagnets (e.g. CrO, LCMO). In contrast to most previous works, we focus on how the superconductor itself is influenced by the proximity effect, and how the generated triplet Cooper pairs manifest themselves in the self-consistently computed density of states (DOS) and the superconducting critical temperature T . We provide a comprehensive treatment of how the superconductor and its properties are affected by the triplet pairs, demonstrating that our theory can reproduce the recent observation of an unusually large zero-energy peak in a superconductor interfaced with a half-metal, which even exceeds the normal-state DOS. We also discuss the recent observation of a large superconducting spin-valve effect with a T change ~1 K in superconductor/half-metal structures, in which case our results indicate that the experiment cannot be explained fully by a long-ranged triplet proximity effect.
超导与强自旋极化磁性材料相互作用，为发现新的自旋电子器件提供了可能，其中自旋三重态库珀对起着关键作用。受最近推导出的能够在扩散极限下描述这种情况的自旋极化准经典边界条件的启发，我们研究了由传统 s 波超导体（例如 Nb、Al）和强自旋极化铁磁绝缘体（例如 EuO、GdN）或半金属铁磁体（例如 CrO、LCMO）组成的混合结构中的涌现物理。与大多数先前的工作相比，我们专注于超导体本身如何受到近邻效应的影响，以及生成的三重库珀对如何在自洽计算的态密度 (DOS) 和超导临界温度 T 中表现出来。我们全面研究了超导体及其性质如何受到三重对的影响，证明我们的理论可以重现最近观察到的与半金属界面的超导体中异常大的零能峰，甚至超过了正常态 DOS。我们还讨论了最近在超导/半金属结构中观察到的大超导自旋阀效应，在这种情况下，我们的结果表明，实验不能完全用长程三重近邻效应来解释。
