Temperature dependence of disorder sensitivity of phonon modes in finite-gap materials

Abstract

The correlation between electronic disorder (quantified by the Urbach energy EU) and phonon linewidth (Γ) is known to be linear. However, both parameters exhibit temperature dependence, raising the question of whether the slope of the Γ vs EU plot remains constant with temperature. In this study, we investigate temperature dependence of the slope, denoted as ζ, which represents the sensitivity of phonon mode to changes in disorder. By applying theoretical models for the temperature dependence of Γ and EU, we derive an expression for ζ(T), revealing its nonlinear behavior at varying temperatures. Our analysis, based on Raman and optical absorption spectra of EuFeO3, demonstrates the explicit temperature dependence of ζ. This provides insights into the disorder sensitivity of vibrational modes, which is crucial for understanding phonon dynamics and transport properties. The findings are further supported by additional investigations on TiO2, emphasizing the utility of combined optical and Raman spectroscopic techniques in probing phonon-resolved disorder sensitivity in materials with finite bandgap where EU can be observed. © 2024 American Physical Society.