Interview for Faculty Position

Vibrational dynamics and heat conduction in amorphous solids

Vincenzo Vitelli

University of Pennsylvania

The development of a theoretical framework that encompasses the dynamical properties of amorphous solids stands as one of the lasting challenges of material science and may unveil further technological potential for a vast class of soft materials such as emulsions, gels, colloidal suspensions as well as granular media and covalent glasses.

In recent years, an intriguing route to studying amorphous materials has emerged from investigating the random geometry of packings comprised of soft spheres interacting with finite-ranged repulsions. The central tenet of this approach is the existence of a zero-temperature jamming transition that occurs at a critical packing fraction, point J, at which the average number of contacts between particles barely satisfies the constraints of mechanical equilibrium.

At point J, the effect of disorder becomes overwhelming and the physics remarkably simple: we find that both the density of states and the thermal diffusivity of the vibrational modes exhibit a plateau extending to zero frequency. This talk focuses on the thermal conductivity of amorphous materials under pressure, which unlike crystals, increases monotonically with temperature. I will show that this distinct property emerges from the vibrational modes at Point J which controls energy transport in a manner akin to a critical point.