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 NbSe2, using a van der Waals device consisting of a vertical stack of graphene-MoS2-NbSe2. The MoS2 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 NbSe2 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 NbSe2 gaps, possibly due to a selection rule which favors coupling between the dots and the orbitals which exhibit this gap.
Bibliographical noteFunding Information:
Devices for this study were fabricated at the Center for Nanoscience and Nanotechnology, the Hebrew University. The authors thank E. Rossi for valuable discussions. The authors thank Tom Dvir and Shahar Simon for helping with the SSM model codes. Funding for this work was provided by a European Research Council Starting Grant (No. 637298, TUNNEL), Israel Science Foundation grant 861/19, and BSF grant 2016320.
© 2021 American Chemical Society.
- 2 band superconductivity
- Quantum Dot
- Resonant Tunneling