Faraday rotation and optical activity are two distinct phenomena which lead to different propagation velocities for the two circular polarizations of light. Faraday rotation is a non-reciprocal effect, dependent on the direction of an external magnetic field, and it forms the basis of important optical devices such as isolators. In contrast, optical activity arises due to a material being chiral, that is having no mirror or inversion symmetry, as in many biological molecules. In a work recently published in Optics Letters, Christofi has modelled a heterostructure combining these two classes of materials and has shown the enhancement of magneto-chiral dichroism—the difference in absorption of unpolarized light depending on the direction of the biasing magnetic field. This heterostructure has a band structure which simultaneously violates time-reversal and space-inversion symmetries, as is required to demonstrate this effect. The theoretical results reported in this paper show that the magneto-chiral dichroism is quite strong, claiming to be two orders of magnitude greater than previous results; thus, it would be of great interest to see this structure realized experimentally.

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