Multipole generalization of the Witten effect in Mie-resonant photonics

Abstract: We present a generalization of the Witten effect on the case of oscillating multipole sources exciting nonreciprocal sphere with effective axion response. We find that the fields outside of the sphere are presented as a superposition of electric and magnetic multipoles. In addition to appearance of cross-polarized component in the radiation, Mie resonances of the system hybridize with each other, exhibiting characteristic double peaks in Mie spectra observed especially clearly for higher-order multipole resonances. This characteristic feature may provide a sensitive probe of axion-type nonreciprocal responses in Mie-resonant photonics.