Influence of the Potential Energy Landscape in Liquid Dynamics

Microscopic molecular theories of supercooled liquids and glasses often posit the presence of long-lived "structures" of some sort in these systems. There is now evidence for these in local packing configurations, and indeed they seem necessary to produce observed heterogeneous dynamic phenomenology. On the other hand, it has long been assumed that, above the melting point, dynamics are unaffected by underlying structure - i.e., that any structure that might exist is averaged out on timescales much shorter than relaxation. By contrast, we find evidence for structures living long enough to influence relaxation not only in supercooled liquids, but in simple liquids far above the melting temperature. We present neutron scattering [1, 2], simulation [3], and ultrafast optical experiments showing that these structures and associated dynamic heterogeneities arise at much higher temperature than is typically expected. We also show that they play a very important role in overall transport and relaxation, even in the liquid state.

[1] Cicerone et al., Physical Review Letters, 113:11, 117801 (2014)

[2] Cicerone et al., The Journal of Chemical Physics 146:5, 054502 (2017)

[3] Cicerone et al., Journal of Non-Crystalline Solids 407, 118-125 (2015)