Are Collective Relaxation Events in Liquids and Glass Bosonic in Nature?

It is held by many that relaxation in supercooled liquids and glasses occurs through some sort of cooperative mechanism. Indeed, cooperative relaxation events are ubiquitously identified in computer simulation, and seem to be associated with motion on a length scale of approximately 0.2σ, and a timescale of approximately 1 ps. We have unambiguously identified the signature of these collective relaxations in neutron and light scattering data, and quantified the fraction (Φ_0) of molecules instantaneously involved in these relaxation events [1-3]. We further show that these motions are indeed the most fundamental element of relaxation [3]. We will present evidence through the temperature dependence of Φ_0 that these fundamental relaxation events (upon which all other relaxation events are built) are bosonic excitations in the liquid or glass. If this proves to be correct, it suggests an approach for understanding relaxation of liquids and glass from a new perspective.

[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] Bender et al., Soft Matter 120:34, 9103-9114 (2020)