  Nontrivial topology in bulk matter has been linked with the existence of
topologically protected interfacial states. We show that a gaseous plasmon
polariton (GPP), an electromagnetic surface wave existing at the boundary of
magnetized plasma and vacuum, has a topological origin that arises from the
nontrivial topology of magnetized plasma. Because a gaseous plasma cannot
sustain a sharp interface with discontinuous density, one must consider a
gradual density falloff with scale length comparable or longer than the
wavelength of the wave. We show that the GPP may be found within a gapped
spectrum in present-day laboratory devices, suggesting that platforms are
currently available for experimental investigation of topological wave physics
in plasmas.

Plasma Physics;Mesoscale and Nanoscale Physics;Fluid Dynamics