Enhanced diffusivity in supercooled liquids

The enhancement of self and probe diffusivity over the Stokes–Einstein values by orders of magnitude is observed in the viscous regime of polymers, molecular glass-formers and supercooled metallic systems. We investigate an alternative to identifying enhanced diffusivity with the fast components of the primary structural relaxation process: high translational mobility is being associated with cooperative dynamics in string-like topologies, which is responsible for fast diffusive particle motion and the slow secondary β-relaxation observed below the dynamic crossover temperature in fragile glass-formers. This approach provides a unifying view of diffusivity across the different classes of glass-forming materials.