Layered superconducting transition metal
dichalcogenides such as NbSe2 have generated intense interest as new
atomically thin quantum materials.
However, they are extremely sensitive to oxidation in the ambient
environment. We have developed a
technique to protect NbSe2 with flakes of hexagonal boron nitride in
inert atmosphere, preventing their oxidation.
Flakes of graphene are used to bridge between metal electrodes and the
NbSe2 to achieve multi-terminal contact, allowing
four-terminal resistivity measurements.
We observe a clear superconducting transition in a bilayer device close
to that of the bulk crystal. The application of a small perpendicular magnetic
field induces a transition to a quantum metallic state. In this phase, the
resistance obeys a unique power-law scaling relation with field, which has not
been observed in previous studies of 2D superconductors.