Excitonic Structure and Dynamics in Two-Dimensional Halide Perovskites

Layered two-dimensional halide perovskites (2D HPs) have emerged as a versatile platform for studying strongly bound excitons in the presence of spin-orbit coupling, structural symmetry breaking, and pronounced coupling to lattice vibrations. In this Mini-Review, we focus on the monolayer limit of this class of materials and highlight recent progress in understanding excitonic fine structure and optical selection rules, chiral and spin-dependent optical response, exciton-phonon coupling and exciton relaxation pathways, and the breakdown of simple band-edge pictures in 2D HPs in which organic and inorganic electronic states hybridize or more complex band structures emerge as a consequence of metal-cation chemistry. Throughout, we emphasize the role of atomistic theoretical and computational frameworks in interpreting the rapidly growing experimental literature. Together, these developments highlight 2D HPs as an unusually rich class of low-dimensional materials for studying spin-optical and excitonic quantum phenomena.