  The study of superconducting materials that also possess nontrivial
correlations or interactions remains an active frontier of condensed matter
physics. NbSe$_2$ belongs to this class of superconductors and recent research
has focused on the two-dimensional properties of this layered material. Here an
investigation of the superconducting-to-normal-state transition in NbSe$_2$ is
detailed, and found to be driven by dynamically-created vortices. Under the
application of RF radiation, these vortices allow for two novel Josephson
effects to be observed. The first is a coupling between Josephson currents and
charge density waves in phase-slip junctions. The second is the Josephson
detection of multi-band superconductivity, which is revealed in an anomalous
magnetic field and RF frequency response of the AC Josephson effect. Our
results shed light on the nature of superconductivity in this material,
unearthing exotic phenomena by exploiting nonequilibrium superconducting
effects in atomically-thin materials.
