Highly Confined Magnetophononic Polaritons and Electron–Phonon Interactions in Atomically Thin MnBi2Te4

Atomically thin materials can strongly confine light into quanta of lattice vibrations, leading to strong light–matter interactions. Some of these materials can exhibit topology, which protects the edge states embedded inside the bulk from backscattering, while some host magnetism, providing another degree of freedom to control topological properties. The simultaneous observation of all of these phenomena in a single material can lead to various applications by enabling light-controlled topological electronic and nanophotonic devices. Here we demonstrate via first-principles density functional perturbation theory calculations that atomically thin MnBi2Te4 is a promising platform for hosting three highly confined, tunable, and long-propagating magnetophononic polaritons. These polaritons strongly modulate exchange interactions, especially the second polariton in 2 SL MnBi2Te4, inducing strong light–matter coupling in the presence of light. Intriguingly, this coupling not only induces an antiferromagnetic-to-ferromagnetic phase transition but also drives an electronic phase transition from trivial to topologically nontrivial states in 2 SL MnBi2Te4. We also show that these polaritonic modes have relatively weak electron–phonon scattering rates and that these scattering rates change with layer thickness and magnetic ordering due to spin–phonon coupling. Overall, our results suggest that MnBi2Te4 is a promising material for topological electronics, nanophotonics, and nanophonics capable of providing greater control of data signals via light.