Spectroscopy of NbSe<sub>2</sub> Using Energy-Tunable Defect-Embedded Quantum Dots.
basic_science · Level V
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- Record sourced from PubMed, PMID 34351777.
- Also identified by DOI 10.1021/acs.nanolett.1c02177.
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Abstract
Quantum dots have sharply defined energy levels, which can be used for high resolution energy spectroscopy when integrated in tunneling circuitry. Here we report dot-assisted spectroscopy measurements of the superconductor NbSe<sub>2</sub>, using a van der Waals device consisting of a vertical stack of graphene-MoS<sub>2</sub>-NbSe<sub>2</sub>. The MoS<sub>2</sub> tunnel barriers host naturally occurring defects which function as quantum dots, allowing transport via resonant tunneling. The dot energies are tuned by an electric field exerted by a back-gate, which penetrates the graphene source electrode. Scanning the dot potential across the superconductor Fermi energy, we reproduce the NbSe<sub>2</sub> density of states which exhibits a well-resolved two-gap spectrum. Surprisingly, we find that the dot-assisted current is dominated by the lower energy feature of the two NbSe<sub>2</sub> gaps, possibly due to a selection rule which favors coupling between the dots and the orbitals which exhibit this gap.