Nature of Sub-diffusion Crossover in Molecular Glass-Formers

A crossover from a non-Gaussian to Gaussian sub-diffusion has been observed ubiquitously in various polymeric/molecular glass-formers. We have developed a framework which generalizes the fractional Brownian motion (fBm) model to incorporate non-Gaussian features by introducing a jump kernel. We illustrate that the non-Gaussian fBm (nGfBm) model accurately characterizes the sub-diffusion crossover. From the solutions of the nGfBm model, we gain insights into the nature of van-Hove self-correlation in non-Gaussian subdiffusive regime, which are found to exhibit exponential tails, providing first such experimental evidence in molecular glass-formers. The results of the model are substantiated using incoherent quasielastic neutron scattering on glass-forming deep eutectic solvents.