Superconductivity protected by spin-valley locking in ion-gated MoS2
Superconductivity protected by spin-valley locking in ion-gated MoS2
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DOI：
10.1038/nphys3580
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发表时间：
2016-02-01
期刊：
影响因子：
19.6
通讯作者：
Iwasa, Yoshihiro
中科院分区：
文献类型：
--
作者：
Saito, Yu;Nakamura, Yasuharu;Iwasa, Yoshihiro
已知对称破缺在具有强自旋轨道相互作用的非中心对称超导体中起着关键作用（SOIs；参考文献1-6）。然而，到目前为止，这些研究主要集中在一种特殊类型的SOI上，称为Rashba SOI（参考文献7），其中电子自旋被锁定在其直角动量上，从而导致平面内螺旋自旋结构。这里我们讨论了二硫化钼（MoS2）中的电场诱导超导性，它表现出一种完全不同类型的本征SOI，表现为能量谷的面外zeeman型自旋极化（8-10）。我们发现在1.5 K时，上临界场约为52 T，这表明与中心对称的传统超导体相比，泡利极限提高了四倍。使用现实的紧密结合计算，我们揭示了这种不寻常的行为是由于谷间配对，这种配对受到塞曼型自旋谷锁定对外部磁场的对称保护。我们的研究揭示了反演不对称性与受限几何SOIs的相互作用，以及它在超导中的作用。
Symmetry-breaking has been known to play a key role in non-centrosymmetric superconductors with strong spin-orbit interactions (SOIs; refs 1-6). The studies, however, have been so far mainly focused on a particular type of SOI, known as the Rashba SOI (ref. 7), whereby the electron spin is locked to its momentum at a right-angle, thereby leading to an in-plane helical spin texture. Here we discuss electric-field-induced superconductivity in molybdenum disulphide (MoS2), which exhibits a fundamentally different type of intrinsic SOI, manifested by an out-of-plane Zeeman-type spin polarization of energy valleys(8-10). We find an upper critical field of approximately 52 T at 1.5 K, which indicates an enhancement of the Pauli limit by a factor of four as compared to that in centrosymmetric conventional superconductors. Using realistic tight-binding calculations, we reveal that this unusual behaviour is due to an inter-valley pairing that is symmetrically protected by Zeeman-type spin-valley locking against external magnetic fields. Our study sheds light on the interplay of inversion asymmetry with SOIs in confined geometries, and its role in superconductivity.