Research Center for Functional Materials, National Institute for Material Science, 1-1 Namiki, Tsukuba 305-0044, Japan.
International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan.
Nano Lett. 2023 Apr 12;23(7):2454-2459. doi: 10.1021/acs.nanolett.2c02777. Epub 2023 Mar 16.
Superconductivity in van der Waals materials, such as NbSe and TaS, is fundamentally novel due to the effects of dimensionality, crystal symmetries, and strong spin-orbit coupling. In this work, we perform tunnel spectroscopy on NbSe by utilizing MoS or hexagonal boron nitride (hBN) as a tunnel barrier. We observe subgap excitations and probe their origin by studying various heterostructure designs. We show that the edge of NbSe hosts many defect states, which strongly couple to the superconductor and form Andreev bound states. Furthermore, by isolating the NbSe edge we show that the subgap states are ubiquitous in MoS tunnel barriers but absent in hBN tunnel barriers, suggesting defects in MoS as their origin. Their magnetic nature reveals a singlet- or a doublet-type ground state, and based on nearly vanishing factors or avoided crossings of subgap excitations, we highlight the role of strong spin-orbit coupling.
范德瓦尔斯材料（如 NbSe 和 TaS）中的超导性是由于维度、晶体对称性和强自旋轨道耦合的影响而具有根本的新颖性。在这项工作中，我们通过利用 MoS 或六方氮化硼（hBN）作为隧道势垒，对 NbSe 进行了隧道光谱学研究。我们观察到了亚带隙激发，并通过研究各种异质结构设计来探究其起源。我们表明，NbSe 的边缘存在许多缺陷态，它们与超导体强烈耦合，并形成安德烈夫束缚态。此外，通过隔离 NbSe 的边缘，我们表明亚带隙态在 MoS 隧道势垒中普遍存在，但在 hBN 隧道势垒中不存在，这表明 MoS 中的缺陷是其起源。它们的磁性揭示了单态或双态基态，并且基于近零的 因子或亚带隙激发的避免交叉，我们强调了强自旋轨道耦合的作用。
