BROKEN SYMMETRY OF THE KINETIC COEFFICIENTS AND SPECULAR POLARIZATIONPHENOMENA

The optical consequences of the violation of thermodynamic equilibrium in a crystal are investigated. If this violation occurs it may lead t o breaking of time reversibility. As a result of this the internal sym metry of the optical susceptibility tensors changes and new ''forbidde n'' tensor components arise. This gives way to some forbidden specular polarization phenomena in optics, observation of which may be used fo r diagnostics of the crystal equilibrium. The wave theory of normal re flection from a crystal interface including consideration of the role of the forbidden components is developed. Two mechanisms for forbidden specular polarization effects are identified, one due to the appearan ce of a contribution to the dielectric tensor which is antisymmetric u nder interchange of tensor indices, and another associated with the sy mmetric contribution to the nonlocal optical response. Crystal point g roup analysis shows that, depending on crystal class, forbidden specul ar polarization effects may be seen with or without a background of '' conventional'' optical activity. The physical conditions for their obs ervation are discussed and recent polarization-sensitive experiments i n optically excited GaAs crystals are explained in terms of the develo ped theory. It is also shown how this approach may be used for the des cription of time-reversal-symmetry-breaking specular optical activity in the superconducting phase of high-T(c) cuprate materials.