Spectroscopy of NbSe₂ Using Energy-Tunable Defect-Embedded Quantum Dots

Quantum dots have sharply defined energy levels, which can be used for high resolution spectroscopy when integrated in tunneling circuitry. Here we report dot-assisted measurements of the superconductor $NbSe_2$, using a van der Waals device consisting vertical stack $graphene-MoS_2-NbSe_2$. The $MoS_2$ tunnel barriers host naturally occurring defects function as quantum dots, allowing transport via resonant tunneling. dot energies are tuned by an electric field exerted back-gate, penetrates graphene source electrode. Scanning potential across Fermi energy, reproduce $NbSe_2$ density states exhibits well-resolved two-gap spectrum. Surprisingly, find that current is dominated lower feature two gaps, possibly due to selection rule favors coupling between and orbitals exhibit this gap.