Electromagnetic response of unconventional superconductors

We derive the current response to the linearly polarized electromagnetic field incident normally on the specular surface of a clean nonconventional superconductor with orbital spontaneous magnetization parallel to the crystal axis and perpendicular to the crystal surface. The result includes the usual part known from the theory of conventional superconductivity, as well as the magneto-optical term typical for superconductors with spontaneous time-reversal breaking. As an application of the basic current-field relation, we consider the Kerr effect for the rotation of the polarization of infrared light reflected from the superconductor surface.