Plasmon Soft Mode in an Organic-Inorganic Hybrid Perovskite

TL;DR

This study investigates plasmon soft modes in azetidinium lead bromide, revealing their temperature dependence and role as a soft mode in the phase transition, with implications for electron-phonon interactions in hybrid perovskites.

Contribution

First observation of inelastic light scattering from underdamped plasmons in AzPbBr3, linking plasmon behavior to phase transition and electron-phonon coupling in hybrid perovskites.

Findings

Plasmons strongly depend on temperature near the phase transition.

Plasmon frequency decreases continuously as temperature approaches TC.

Impedance analysis indicates electron-phonon coupling influences plasmon properties.

Abstract

We report inelastic light scattering from underdamped plasmons in azetidinium lead bromide (AzPbBr3). The plasmons are very strongly temperature dependent and serve as a soft mode for the semiconductor-insulator phase transition near TC {\guillemotright} 150 K, demonstrating a continuous decrease in hole concentration np(T) by at least a factor of four and implying a nearly tricritical transition. The plasmon frequency and linewidth agree with independent measurements, and the impedance analysis reveals a frequency dependence (modelled by a constant phase element, CPE) that can be identified as due to electron-phonon coupling. The dependence of plasmon frequency upon (TC-T) is analogous to that for magnons in magnetic insulators or soft transverse optical phonons in ferroelectrics and ferroelastics, or for phasons in incommensurately modulated insulators.