biostudies-literatureKarnatak PCore Research for Evolutional Science and TechnologySwiss National Science FoundationEuropean Research CouncilSwiss Nanoscience Institute, University of BaselJapan Society for the Promotion of Science2454-2459https://www.ebi.ac.uk/biostudies/studies/S-EPMC10103330biostudies-literatureUnknown23(7)Superconductivity in van der Waals materials, such as NbSe₂ and TaS₂, is fundamentally novel due to the effects of dimensionality, crystal symmetries, and strong spin-orbit coupling. In this work, we perform tunnel spectroscopy on NbSe₂ by utilizing MoS₂ 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 NbSe₂ hosts many defect states, which strongly couple to the superconductor and form Andreev bound states. Furthermore, by isolating the NbSe₂ edge we show that the subgap states are ubiquitous in MoS₂ tunnel barriers but absent in hBN tunnel barriers, suggesting defects in MoS₂ as their origin. Their magnetic nature reveals a singlet- or a doublet-type ground state, and based on nearly vanishing <i>g</i> factors or avoided crossings of subgap excitations, we highlight the role of strong spin-orbit coupling.Nano lettersOrigin of Subgap States in Normal-Insulator-Superconductor van der Waals Heterostructures.PMC1010333020H00354JPMJCR15F378741419H05790Karnatak PSchonenberger CForro LWatanabe KMingazheva ZBerger HTaniguchi TfalseOrigin of Subgap States in Normal-Insulator-Superconductor van der Waals Heterostructures.Superconductivity in van der Waals materials, such as NbSe₂ and TaS₂, is fundamentally novel due to the effects of dimensionality, crystal symmetries, and strong spin-orbit coupling. In this work, we perform tunnel spectroscopy on NbSe₂ by utilizing MoS₂ 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 NbSe₂ hosts many defect states, which strongly couple to the superconductor and form Andreev bound states. Furthermore, by isolating the NbSe₂ edge we show that the subgap states are ubiquitous in MoS₂ tunnel barriers but absent in hBN tunnel barriers, suggesting defects in MoS₂ as their origin. Their magnetic nature reveals a singlet- or a doublet-type ground state, and based on nearly vanishing <i>g</i> factors or avoided crossings of subgap excitations, we highlight the role of strong spin-orbit coupling.2023-01-01T00:00:00Z2023 Apr2025-04-04T12:44:09.893Z2025-04-04T12:44:09.893ZS-EPMC101033303692693410.1021/acs.nanolett.2c02777