Nonreciprocity in the optical reflection of magnetoplasmas

We measured the reflectivity on a slab of $n$-type InSb with an incident angle of 45° with different far-infrared laser frequencies of 337-, 311-, and 119-μm wavelengths as a function of applied magnetic field $B$ between 0 and 10 T. The field was applied in the plane of the surface perpendicular to the reflection plane. We observed clear evidence of nonreciprocal behavior in the reflectivity with respect to field reversal and light-propagation reversal. A simple Drude model accounts satisfactorily for this effect. The influence of damping, crucial for the existence of this effect, is discussed within the framework of electrodynamics as well as with thermodynamic arguments, generalizing Kirchhoff's law of radiation.