Breunig Daniel, Burset Pablo, Trauzettel Björn
Institute for Theoretical Physics and Astrophysics, University of Würzburg, 97074 Würzburg, Germany.
Department of Applied Physics, Aalto University, 00076 Aalto, Finland.
Phys Rev Lett. 2018 Jan 19;120(3):037701. doi: 10.1103/PhysRevLett.120.037701.
In superconducting spintronics, it is essential to generate spin-triplet Cooper pairs on demand. Up to now, proposals to do so concentrate on hybrid structures in which a superconductor (SC) is combined with a magnetically ordered material (or an external magnetic field). We, instead, identify a novel way to create and isolate spin-triplet Cooper pairs in the absence of any magnetic ordering. This achievement is only possible because we drive a system with strong spin-orbit interaction-the Dirac surface states of a strong topological insulator (TI)-out of equilibrium. In particular, we consider a bipolar TI-SC-TI junction, where the electrochemical potentials in the outer leads differ in their overall sign. As a result, we find that nonlocal singlet pairing across the junction is completely suppressed for any excitation energy. Hence, this junction acts as a perfect spin-triplet filter across the SC, generating equal-spin Cooper pairs via crossed Andreev reflection.
在超导自旋电子学中，按需产生自旋三重态库珀对至关重要。到目前为止，相关提议主要集中在混合结构上，即超导体（SC）与磁有序材料（或外部磁场）相结合。相反，我们发现了一种在没有任何磁有序的情况下创建和隔离自旋三重态库珀对的新方法。之所以能够取得这一成果，是因为我们驱动了一个具有强自旋轨道相互作用的系统——强拓扑绝缘体（TI）的狄拉克表面态——使其偏离平衡态。具体而言，我们考虑一个双极TI-SC-TI结，其中外部引线中的电化学势在整体符号上有所不同。结果，我们发现对于任何激发能量，结上的非局域单重态配对都被完全抑制。因此，这个结在整个超导体上充当了一个完美的自旋三重态滤波器，通过交叉安德烈夫反射产生等自旋库珀对。
