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

TL;DR

This study reveals how molecular chirality in hybrid perovskites influences the inorganic lattice through coherent phonons, advancing understanding of chiral optoelectronic properties.

Contribution

It uncovers the microscopic mechanism of chirality transfer via coherent lattice vibrations in chiral hybrid perovskites, combining spectroscopy and ab-initio calculations.

Findings

Identification of a ~5.7 meV coherent phonon mode

Strong coupling of this mode to excitons in chiral perovskite

Absence of this mode in racemic analogue

Abstract

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.