Gyrotropic Birefringence—Phenomenological Theory

A phenomenological theory of gyrotropic birefringence is presented. Since the magnetic classes in which gyrotropic birefringence is allowed are among those in which the magnetoelectric effect may occur, the constitutive relations between the complex amplitudes of the fields are so written as to incorporate both these effects simultaneously. All induced effects are then combined in a suitably renormalized electric dipole moment. For the case of lossless media, the gyrotropic birefringence property tensor has 18 linearly independent components before crystalline symmetry considerations are introduced. It is shown that a physical basis for these 18 independent quantities may be found in electric quadrupole and magnetoelectric effects, with the former contributing ten independent quantities and the latter eight. In particular, the compounds $Cr2O3$ and $MnTiO3$⁠, in which an experimental observation of gyrotropic birefringence may be possible, are considered. Finally, the closely related effect of natural optical activity is discussed and correlated with the point of view presented here.