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Highly confined phonon polaritons in monolayers of oxide perovskites

Two-dimensional (2D) materials are able to strongly confine light hybridized with collective excitations of atoms, enabling electric-field enhancements and novel spectroscopic applications. Recently, freestanding monolayers of oxide perovskites have been synthesized, which possess highly infrared-active phonon modes and a complex interplay of competing interactions. In this study, we evaluate central figures of merit for phonon polaritons in the tetragonal phases of the 2D perovskites SrTiO$_3$, KTaO$_3$, and LiNbO$_3$, using density functional theory calculations. Specifically, we compute the 2D phonon-polariton dispersions, the propagation-quality, confinement, and deceleration factors, and we show that they are comparable to those found in the prototypical 2D dielectric hexagonal boron nitride. Our results suggest that monolayers of oxide perovskites are promising candidates for polaritonic platforms in the terahertz spectral range that enable possibilites to control complex phases of matter through strongly enhanced electromagnetic fields.