Statistical field theory of equilibrium amorphous solids and the intrinsic heterogeneity distributions that characterize them

Abstract

A rich variety of amorphous solids are found in nature and technology, including ones formed via the vulcanization of long, flexible molecules. A special class -- those featuring a wide gap between the long timescales over which constraints in them release and the much shorter timescales over which their unconstrained freedoms relax -- exhibit states of thermodynamic equilibrium and are thus amenable to the framework of equilibrium statistical physics. The approach reviewed here is the least specific -- and thus the most general -- approach to the statistical mechanics of equilibrium amorphous solid-formers: statistical field theory. An overview is given of the key elements and results of this theory. The field of the theory is constructed to detect and diagnose the amorphous solid state. Its form turns out to be unusual, in ways that are essential for its application, so it is examined in detail, as is the form of the field theory controlling the field. What this theory can predict for the equilibrium properties of amorphous solids is then discussed, including: the transition to the amorphous solid state and the heterogeneity of the resulting solid; the impact of fluctuations on the transition and connections with percolation theory; the pattern of symmetry-breaking and the nature of the resulting elasticity; and field correlations and the information they provide. Emphasis is placed on the idea, peculiar to amorphous solids, that their equilibrium states are naturally characterized in terms of distributions that capture the intrinsic spatial heterogeneity of the thermal motions of their constituents. The theory's field has an internal structure that subtly encodes this information, via the wave-vector dependencies of the average field and its correlations. Reflections are made on the applicability of theses ideas and results to a range of amorphous solids and related systems.