Phonon-Mediated Chirality Transfer from Organic Cation to Inorganic lattice in Hybrid Perovskites

Two-dimensional hybrid metal halide perovskites combine strong spin-orbit coupling, soft lattice dynamics and molecular tunability, making them promising platforms for chiral optoelectronics and spin dependent phenomena. While chiral organic spacers are known to induce optical activity, the microscopic mechanism by which molecular chirality couples to the inorganic lattice remains unclear. Here, we investigate coherent vibrational dynamics in the chiral perovskite ($R$-MBA)${}_2$PbI${}_4$ and its racemic analogue using transient absorption spectroscopy, complemented by Raman spectroscopy and ab-initio calculations. We identify a coherent phonon at ~5.7 meV that couples strongly to excitons in the chiral material but is absent in the racemic counterpart. This mode is assigned to lattice vibrations involving coupled motion of the chiral spacer and Pb-I framework, including rotational displacement patterns. These results establish coherent lattice motion as a pathway for mediating chiral responses in hybrid materials.