Department of Applied Science and Technology , Politecnico di Torino , 10129 Torino , Italy.
Cambridge Graphene Centre , University of Cambridge , Cambridge CB3 OFA , United Kingdom.
Nano Lett. 2018 Aug 8;18(8):4821-4830. doi: 10.1021/acs.nanolett.8b01390. Epub 2018 Jul 16.
Layers of transition metal dichalcogenides (TMDs) combine the enhanced effects of correlations associated with the two-dimensional limit with electrostatic control over their phase transitions by means of an electric field. Several semiconducting TMDs, such as MoS, develop superconductivity (SC) at their surface when doped with an electrostatic field, but the mechanism is still debated. It is often assumed that Cooper pairs reside only in the two electron pockets at the K/K' points of the Brillouin Zone. However, experimental and theoretical results suggest that a multivalley Fermi surface (FS) is associated with the SC state, involving six electron pockets at Q/Q'. Here, we perform low-temperature transport measurements in ion-gated MoS flakes. We show that a fully multivalley FS is associated with the SC onset. The Q/Q' valleys fill for doping ≳ 2 × 10 cm, and the SC transition does not appear until the Fermi level crosses both spin-orbit split sub-bands Q and Q . The SC state is associated with the FS connectivity and promoted by a Lifshitz transition due to the simultaneous population of multiple electron pockets. This FS topology will serve as a guideline in the quest for new superconductors.
过渡金属二卤化物（TMD）的各层通过电场对其相变进行静电控制，结合了二维极限相关的关联增强效应。当用静电场掺杂时，几种半导体 TMD，如 MoS2，在表面会发展出超导性（SC），但机制仍存在争议。通常假设库珀对仅存在于布里渊区的 K/K' 点的两个电子口袋中。然而，实验和理论结果表明，多谷费米表面（FS）与 SC 状态相关，涉及 Q/Q' 处的六个电子口袋。在这里，我们在离子门控 MoS 薄片中进行低温输运测量。我们表明，完全多谷 FS 与 SC 起始相关。当掺杂 ≳ 2×10 cm 时，Q/Q' 谷填充，并且只有当费米能级穿过 Q 和 Q 自旋轨道分裂子带时，SC 转变才会出现。SC 状态与 FS 的连通性有关，并由于多个电子口袋的同时填充而通过 Lifshitz 转变得到促进。这种 FS 拓扑结构将成为寻找新超导体的指南。
