Join us to hear from Omer Yaffe about his research at the Weizmann Institute of Science!

Abstract: Anharmonicity refers to deviations from a purely quadratic lattice potential, where atomic motions are no longer independent harmonic vibrations but interact nonlinearly. While often treated as a small correction, anharmonicity in many solids fundamentally shapes their structure and dynamics. In this talk, I will describe how our work uses Raman spectroscopy to trace the consequences of anharmonic lattice dynamics from equilibrium fluctuations to nonequilibrium behavior.
 

I will first focus on equilibrium Raman spectroscopy in the low-frequency (THz) regime. By analyzing temperature- and polarization-dependent Raman lineshapes, we probe couplings between vibrational degrees of freedom in crystals, glasses, and liquids. Combined with modeling, these measurements show how anharmonic interactions reshape the free-energy landscape, relax Raman selection rules, and give rise to liquid-like scattering signatures in structurally ordered solids.

I will then introduce a new experimental approach for accessing nonequilibrium lattice dynamics. Using time-correlated single-photon counting–based, time-resolved spontaneous Raman spectroscopy, we track how solids reorganize in time after being driven away from equilibrium, while preserving high spectral resolution. Crystalline silicon serves as a model system to demonstrate the capabilities of this method, which spans timescales from hundreds of picoseconds to milliseconds.

I will conclude by discussing how this approach can be extended to address broader questions, including charge–lattice interactions, polaron relaxation, and the mechanisms and dynamics of structural phase transitions driven by external perturbations.

Host: Mike Ruggiero | michael.ruggiero@rochester.edu