Origin of Subgap States in Normal-Insulator-Superconductor van der Waals Heterostructures.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 36926934.
- Also identified by DOI 10.1021/acs.nanolett.2c02777 and PMC identifier 10103330.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
Superconductivity in van der Waals materials, such as NbSe<sub>2</sub> and TaS<sub>2</sub>, 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<sub>2</sub> by utilizing MoS<sub>2</sub> 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<sub>2</sub> hosts many defect states, which strongly couple to the superconductor and form Andreev bound states. Furthermore, by isolating the NbSe<sub>2</sub> edge we show that the subgap states are ubiquitous in MoS<sub>2</sub> tunnel barriers but absent in hBN tunnel barriers, suggesting defects in MoS<sub>2</sub> 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.