Broken symmetry of the kinetic coefficients and specular polarization phenomena

The optical consequences of the violation of thermodynamic equilibrium in a crystal are investigated. If this violation occurs it may lead to breaking of time reversibility. As a result of this the internal symmetry of the optical susceptibility tensors changes and new ‘‘forbidden’’ tensor components arise. This gives way to some forbidden specular polarization phenomena in optics, observation of which may be used for diagnostics of the crystal equilibrium. The wave theory of normal reflection 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 appearance of a contribution to the dielectric tensor which is antisymmetric under interchange of tensor indices, and another associated with the symmetric contribution to the nonlocal optical response. Crystal point group analysis shows that, depending on crystal class, forbidden specular polarization effects may be seen with or without a background of ‘‘conventional’’ optical activity. The physical conditions for their observation are discussed and recent polarization-sensitive experiments in optically excited GaAs crystals are explained in terms of the developed theory. It is also shown how this approach may be used for the description of time-reversal-symmetry-breaking specular optical activity in the superconducting phase of high-${\mathit{T}}_{\mathit{c}}$ cuprate materials.