We show that reversed Vavilov-��erenkov radiation occurs simultaneously with the forward output in naturally existing materials when an electric charge moves with a constant velocity perpendicular to the planar interface between two magnetoelectric media. Using the Green's function in the far-field approximation we calculate the angular distribution of the radiated energy per unit frequency obtaining a non-zero contribution in the backward direction.

Four pages, 1 figure, tex, ws-procs9x6-cpt19.cls, Presented at the Eighth Meeting on CPT and Lorentz Symmetry, Bloomington, Indiana, May 12-16, 2019, typos corrected