The traditional understanding in materials science considers single crystals nearly perfect in their ordered structures, represented by a unit cell that informs their mechanical and electronic properties. Our studies challenge this paradigm by demonstrating large deviations from the predictions made by the unit cell model to materials properties in systems such as halide perovskites, ion conductors, and organic semiconductors. 

Utilizing Raman spectroscopy, our efforts focus on the detailed examination of thermal motions and their implications on single crystals. The discrepancies between experimental observations and theoretical predictions are explored, particularly emphasizing the interaction between vibrational modes and their impact on material properties.

 A significant aspect of this research is detailed in our recent publication, where we propose a new model for second-order Raman scattering to account for the nonmonotonic temperature dependence observed in perovskite single crystals. This model, supported by numerical simulations, identifies low-frequency anharmonic features as key players in light scattering processes, highlighting a transition between two minima of a double-well potential surface. Our findings provide a more accurate understanding of the structural dynamics within disordered crystals and suggest broader applications for designing materials with enhanced electronic and optical functionalities.