Superheating and melting phenomena of a vibrated granular layer of cubic particles

We report the combined results of both experiments and molecular dynamics simulations, carried out to investigate superheating phenomena in vertically vibrated granular matter. Specifically, we consider a system of cubic particles, densely packed in a squared-lattice array and subjected to different acceleration shaking strengths Γ. Below a critical value Γ_{c}∼3.2, the excited crystalline array remains stable indefinitely, whereas for a fixed Γ>Γ_{c}, the system stays first in a metastable solid phase and then it transitions progressively into a liquid phase, during a Γ-dependent timescale τ_{m}. The value of Γ_{c} required to observe metastable superheated states for cubic particles is considerably larger than the value previously reported for spherical beads (Γ_{c}^{sph}∼1.4), which is attributed to a more efficient energy dissipation process due to interparticle friction, that also lengthens substantially the lifetime of the superheated crystal. Notably, however, the exponents of the power scaling laws for τ_{m}(Γ) are very similar for both geometries, suggesting universality in this transition. Our findings also show that the transition from the superheated-solid to the liquid state of the vibrated system is well captured by a Kolmogorov-Johnson-Mehl-Avrami equation, routinely employed to describe phase transformations in thermal systems.