Multiband Superconductivity in $2H$-NbSe$_{2}$ Probed by Cryomagnetic STM Spectroscopy*

Using a novel magnetic field geometry, we study multiband pairing in single crystals of superconducting $2H$-NbSe$_{2}$ under finite superfluid momentum. Spectroscopy and conductance imaging were performed with a scanning tunneling microscope (STM) at 300 mK and in a field of up to 9 T, applied in the $ab$-plane. We observed multiple spectral features that evolve systematically with field, and a two-sloped zero-bias conductance that dips anomalously at 0.7 T. Our analysis yields distinct evidence for multiple gaps coming from the various Fermi-surface sheets, and has possible implications on the origin of the coexisting charge density wave order.