Phenomenological theory of photomagnetoelectric effects Application to the directional photovoltaic effect in LiNbO3

We propose a phenomenological theory working out light illumination effects on the equilibrium values of any macroscopic crystal tensor (polarization, magnetization, susceptibilities, strain tensor, elastic coefficients...). it also encompasses non-equilibrium light-induced quantities such as an electric current and heat flow. We use a single phenomenological approach based on Wigner spherical functions for predicting symmetry-related photo-induced phenomena, including photovoltaic, photoelectric, photomagnetic, photorefractive, photogalvanic, photoelastic and optic rectification phenomena. For each crystal magnetic point group and each tensor type, response functions are calculated vs. the propagation and polarization directions of the incident electromagnetic beam. Their forms are determined by crystal and light symmetry group interconnection. We pay special attention to time and space reversal symmetries, which play a dominant role in the intricate symmetry breakdowns of multiferroic materials. Photovoltaic and photo-magneto-electric effects in LiNbO3 illustrate our theory.