Orthogonal-Phase-Velocity Propagation of Electromagnetic Plane Waves
  In an isotropic, homogeneous, nondissipative, dielectric-magnetic medium that is simply moving with respect to an inertial reference frame, planewave solutions of the Maxwell curl postulates can be such that the phase velocity and the time-averaged Poynting vector are mutually orthogonal. Orthogonal-phase-velocity propagation thus adds to the conventional positive-phase-velocity propagation and the recently discovered negative-phase-velocity propagation that is associated with the phenomenon of negative refraction. 
Tom G. Mackay (University of Edinburgh), Akhlesh Lakhtakia   (Pennsylvania State University)