Axion quasiparticle and axion polariton in antiferromagnetic topological insulators
In plain words
In antiferromagnetic topological insulators, magnetic fluctuations should make the axion angle oscillate, producing a collective excitation that mixes with light, and its coupling to light has not been observed.
Precise statement
Li, Wang, Qi and Zhang (Nature Physics, 2010) predicted that in antiferromagnetic topological insulators the axion field $\theta(r,t)$ acquires dynamics through coupling to the Neel order, giving an axion quasiparticle that hybridizes with photons into axion polaritons under a static magnetic field. Determine whether the polariton exists in a candidate material ($\mathrm{MnBi_2Te_4}$ family) and measure the axion mass and photon coupling. An answer is spectroscopic detection with the predicted dependence on applied field.
What would settle it
Terahertz or microwave spectroscopy showing a polariton gap that scales with the applied field and disappears outside the antiferromagnetic phase.
Status in the literature
Unverified note: it names recent work and was partly written without a live literature search; it awaits a check by an editor.
A 2025 ultrafast-optics study reported coherent axion-mode oscillations in 2D $\mathrm{MnBi_2Te_4}$; axion-polariton hybridization with light is not observed as of 2026, to this survey's knowledge.
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