Plasma Physics Special Seminar - Jerome Daligault, Ph.D., Los Alamos National Laboratory
"Universal Character of Atomic Motions at the Liquid-Solid Transition" by Jerome Daligault, Ph.D., Los Alamos National Laboratory
Abstract: Nearly all fluids freeze into a periodic structure when gently cooled or compressed. Past a particular point, the liquid state becomes metastable with respect to the crystalline state. Small crystal embryos spontaneously form and re-dissolve via thermal fluctuations, unless their size exceeds a critical value beyond which they irreversibly grow and coalesce. This traditional description of freezing, however, does not elucidate what happens on the atomic level that allows the system to discover the crystalline order. In this work, we show evidence from computer simulations of a universal character of atomic motions in simple liquids that heralds the freezing transition. We find that the first-passage properties of the atomic dynamics at the freezing point, namely the mean time to first reach a distance and the associated probability distributions, are insensitive to the nature of the interparticle force law. The location of the freezing transition is concomitant with a universal degree of localization of atomic motions above which the delicate balance between the disordering effects of thermal agitation and the ordering effects of interactions can be destabilized in favour of the periodic order. These findings, which contrast with the acknowledged non-universal character of freezing, open up a new perspective for understanding the mechanisms of this important first-order transition.