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The electro‐optic (EO) effect is one of the physical mechanisms enabling the dynamic response of metasurfaces, which motivates the analysis of nanoantenna arrays integrated with EO materials. It was shown earlier that chalcophosphate Sn₂P₂S₆metasurfaces can enable significant shifts of multipolar resonances by enhancing the EO response near the Curie temperature. The present work explores how the refractive index of EO materials impacts resonance shifts in metasurfaces with multipolar resonances. It is numerically demonstrated that EO nanoantennas can support pronounced multipolar resonances despite their moderate refractive index, enabling strong light confinement and substantial EO tuning, and that multipolar components of even parity exhibit the highest sensitivity to variations in the refractive index of the nanoantennas. For moderate refractive indices varying from 2.3 to 3.0, it is found that, for a given resonance, the wavelength shift resulting from a refractive index change has a relatively weak dependence on the index itself. This suggests that the refractive index plays only a marginal role in enhancing the EO shift in active photonic devices, and instead, other considerations for material selection, such as the EO coefficient magnitude, the transparency window, and ease of processing, should be of primary concern. 

Chalcophosphate metasurfaces exhibit a significant electro-optic shift in multipolar resonances due to large electric-field-induced refractive index changes, obtainable with in-plane or out-of-plane biasing.