Methodology to Probe Disorder Contribution in Raman Linewidth via Optical Absorption Spectroscopy in Orthoferrite EuFeO₃

The individual impact of disorder on different phonon modes has been investigated for orthoferrite EuFeO3 by perceiving a correlation between temperature-dependent Raman linewidth (Δ) and Urbach energy (EU). It has been found that the plot of Δ versus EU exhibits a linear relationship, whose slope (ζ) differs for each Raman mode. Interestingly, the Raman mode exhibiting larger temperature variation in width is found to acquire a larger slope. This has been understood as eclectic contribution of disorder toward altering the mode-widths. Furthermore, a careful analysis hints that parameter ζ may contain information of overlap between discrete (phonon) and electronic continuum (∼Urbach tail) states. This may be seen as a selective impact of disorder on individual phonons in view of the electron-phonon interaction. Hence, the slope of the linear plot between Δ and EU has been realized as a parameter that may represent the individual disorder contribution to modify Raman width of each mode, and thereby ζ has been interpreted to be the disorder-coupling parameter.