Discovery of enhanced lattice dynamics in a single-layered hybrid perovskite

TL;DR

This study uncovers how reducing the dimensionality in layered hybrid perovskites enhances lattice dynamics, revealing a long-lived coherent phonon mode in single-layered systems through advanced spectroscopy and simulations.

Contribution

It demonstrates the distinct lattice vibrational behaviors between single- and double-layered perovskites using combined experimental and computational methods.

Findings

Long-lived coherent phonon mode in single-layered perovskites

No vibrational coherence observed in double-layered perovskites

Dimensional reduction dramatically alters lattice environment

Abstract

Layered hybrid perovskites have attracted much attention in recent years due to their emergent physical properties and exceptional functional performances, but the coexistence of lattice order and structural disorder severely hinders our understanding of these materials. One unsolved problem regards how the lattice dynamics are affected by the dimensional engineering of the inorganic frameworks and the interaction with the molecular moieties. Here, we address this question by using a combination of high-resolution spontaneous Raman scattering, high-field terahertz spectroscopy, and molecular dynamics simulations. This approach enables us to reveal the structural vibrations and disorder in and out of equilibrium and provides surprising observables that differentiate single- and double-layered perovskites. While no distinct vibrational coherence is observed in double-layer perovskites, we discover that an off-resonant terahertz pulse can selectively drive a long-lived coherent phonon mode through a two-photon process in the single-layered system. This difference highlights the dramatic change in the lattice environment as the dimension is reduced. The present findings pave the way for the ultrafast structural engineering of hybrid lattices as well as for developing high-speed optical modulators based on layered perovskites.