Fig. 2: Polarization-angle resolved Raman Spectra and Symmetry Analysis.
From: Coupling of electronic transition to ferroelectric order in a 2D semiconductor
a, b Polarization-angle resolved Raman spectra of NbOI2 at RT with incident polarization in the yz plane (y = b-axis, z = c-axis) and scattering polarization parallel (a) or perpendicular (b) to incident polarization. 0 degree is referenced to the crystallographic c-axis. The color bar represents the Raman scattering intensity (normalized to the highest intensity for clarity). pp represents parallel polarization and cp represents cross polarization. c Polar plot corresponding to spectral cut from (a) and (b) at 3.137 THz mode (P2 mode). Solid lines are fitting curves obtained by the global fit to both pp and cp data with Supplementary Equations 1 and 2 in Supplementary Text, respectively. d Parallel polarized Raman spectrum with incident polarization aligned to either the b or c-axis. e Simulated Raman spectra at 300 K with parallel polarization. f Simulated polar plot of the phonon mode at a calculated frequency of 2.830 THz. An empirical term, \(\cos {\varphi }_{{\rm{c}}-{\rm{b}}}\), that was deduced from the tensor fit of the experimental P2 mode data and describing the phase difference between two tensor elements was applied to the simulation to account for the finite absorption of incident light.
