  We calculate the dispersion relations for electromagnetic waves propagating
at the interface between two dissimilar Drude metals in an external magnetic
field B parallel to the interface. The propagating modes are bound to the
inteface and travel perpendicular to B. In certain frequency ranges, the waves
can propagate in one direction only. The frequency range for these one-way
modes increases with increasing B. One group of modes occurs at moderate
frequencies, between the lower and upper plasma frequencies of the two metals.
The other occurs at much lower frequencies, between their lower and upper
cyclotron frequencies. We discuss possible ways to realize such modes in real
materials, including dissimilar superconductors.
