- Department of Physics, The Pennsylvania State University
APP-260617-0001condensed-matter-physicsarXiv:2606.04341Release v1.0.0Listed Jun 17, 2026
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Summary
Under appropriate static electric (E₀ ‖ ŷ) and magnetic (B₀ ‖ ẑ) fields applied simultaneously to a dynamical axion insulator, axion-polaritons — hybrid axion-photon collective modes — acquire a nonreciprocal dispersion ω(k) ≠ ω(−k). This arises because the axion-photon coupling is direction-dependent: photons propagating in opposite directions hybridize with the axion with different strengths (g₊ ≠ g₋). Neither field alone is sufficient; the simultaneous breaking of inversion symmetry (by E₀) and time-reversal symmetry (by B₀) produces the term 2𝓔𝓑kω in the quartic dispersion (Eq. 4) that is the microscopic origin of nonreciprocity.
The paper identifies a special regime of perfect nonreciprocity when E₀ = c′B₀: here ω = c′k is an exact solution of the quartic, meaning the right-moving photon is completely decoupled from the axion source while the counter-propagating photon hybridizes strongly — a one-way coupling with no analogue in prior axion-polariton work. This direction-dependent coupling manifests directly as an optical isolator: a finite slab transmits light left-to-right with high efficiency while right-to-left transmission is exponentially suppressed near the axion resonance. The results propose nonreciprocal axion-polaritons as a new experimental probe of axion quasiparticles, with material parameters motivated by GHz-frequency magnon measurements in MnBi₂Te₄.