Optical magnetoelectric effect in multiferroic materials: evidence for a Lorentz force acting on a ray of light.

We theoretically propose that the optical analog of a Lorentz force acting on a ray of light is realized in multiferroic materials such as GaFeO3 showing the magnetoelectric effect. The toroidal moment T --> = sigma(j)r(j) x S(j) plays the role of a "vector potential," while its rotation corresponds to a "magnetic field" for photons. Hence, the light is subject to the Lorentz force when propagating through the domain wall region of the ferromagnetic or ferroelectric order. A realistic estimate on the magnitude of this effect is given.