Mobile-group dominated dynamics and sequence of mobility transitions in facilitated random walk model of glass.

Glassy dynamics has been a topic of ongoing debate for decades. We investigate a recently proposed facilitated random walk (FRW) model, which is a kinetically constrained model (KCM) with random constraints and is a coarse-grained version of the distinguishable-particle lattice model (DPLM) of glass. Dynamics in the FRW model with a finite density of particles are dominated by mobile groups of particles enjoying emergent facilitated dynamics. We observe a diffusion coefficient power-law with respect to the particle density, with the exponent identified as the dominant mobile group size. In addition, simplified FRW systems initiated with a few particles at the same site exhibit a sequence of mobility transitions, explaining the dynamical dominance of mobile groups. For such systems with two particles, the mobility transition point is calculated exactly.