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arXiv · 2207.05741

Origin of subgap states in normal-insulator-superconductor van der Waals heterostructures

Paritosh Karnatak·Zarina Mingazheva·Kenji Watanabe·Takashi Taniguchi·Helmuth Berger·László Forró·Christian Schönenberger
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Abstract

Superconductivity in van der Waals materials, such as NbSe$_{2}$ and TaS$_{2}$, 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$_{2}$ by utilizing MoS$_{2}$ 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$_{2}$ hosts many defect states, which strongly couple to the superconductor and form Andreev bound states. Furthermore, by isolating the NbSe$_{2}$ edge we show that the subgap states are ubiquitous in MoS$_{2}$ tunnel barriers, but absent in hBN tunnel barriers, suggesting defects in MoS$_{2}$ as their origin. Their magnetic nature reveals a singlet or a doublet type ground state and based on nearly vanishing g-factors or avoided-crossing of subgap excitations we highlight the role of strong spin-orbit coupling.

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Paritosh Karnatak, Zarina Mingazheva, Kenji Watanabe, Takashi Taniguchi, Helmuth Berger, László Forró, Christian Schönenberger. 2022-07-12. Origin of subgap states in normal-insulator-superconductor van der Waals heterostructures. https://doi.org/10.1021/acs.nanolett.2c02777

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