Abstract
The nature of defects in amorphous materials, analogous to vacancies and dislocations in crystals, remains elusive. Here, we explore their nature in a three-dimensional microscopic model glass-former that describes granular, colloidal, atomic and molecular glasses by changing the temperature and density. We find that all glasses evolve in a very rough energy landscape, with a hierarchy of barrier sizes corresponding to both localized and delocalized excitations. Collective excitations dominate in the jamming regime relevant for granular and colloidal glasses. By moving gradually to larger densities describing atomic and molecular glasses, the system crosses over to a regime dominated by localized defects and relatively simpler landscapes. We quantify the energy and temperature scales associated to these defects and their evolution with density. Our results pave the way to a systematic study of low-temperature physics in a broad range of physical conditions and glassy materials.
Highlights
The nature of defects in amorphous materials, analogous to vacancies and dislocations in crystals, remains elusive
We study the temperature evolution of the relaxation time τα of density correlations in the equilibrium fluid, using molecular dynamics (MD) simulations
We study the nature of excitations and defects through extensive simulations of a three-dimensional WCA glass former
Summary
The nature of defects in amorphous materials, analogous to vacancies and dislocations in crystals, remains elusive. Typically modeled by simple Lennard–Jones (LJ) interaction potentials, low-frequency excitations are phonon-like (with peculiar properties)[18,19,20,21], and defects are localized, with a few particles jumping between two local minima and slightly perturbing their neighbors, giving rise to twolevel systems that play an important role in the low-temperature thermal properties of glasses[7,22]. This phenomenology has been numerically confirmed in simple LJ-like glass models[6,23,24]
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