Breaking Lorentz Reciprocity in the Weyl Semimetal Co₃Sn₂S₂ to Enable Time-Asymmetric Photonics

Weyl semimetals that break time-reversal symmetry are predicted to exhibit giant magneto-optical effects, the optical response from which can be described using an axion electrodynamics formalism. The formalism produces a dielectric tensor with non-vanishing off-diagonal components even without external magnetic fields; thus, these systems are interesting examples of violations of Lorentz reciprocity and Kirchhoff’s Law in small form factors.
Here we use electromagnetic and ab initio simulations, and experimental measurements of infrared light scattering to demonstrate the breaking of Lorentz reciprocity in the ferromagnetic phase of Co₃Sn₂S₂ through calculations and measurement of nonequivalent reflection coefficients of opposing channels. We measure, via ellipsometry, the components of the dielectric tensor and discuss the implications of this result on the feasibility of magnetic Weyl semimetals for time-asymmetric photonics applications.

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