Amorphous solids as fuzzy crystals: A Debye-like theory of low-temperature specific heat

TL;DR

This paper introduces a quantum mechanical model treating amorphous solids as fuzzy crystals, successfully explaining low-temperature specific heat and the boson peak through an analytical theory aligned with experimental data.

Contribution

It presents a novel, mathematically simple framework modeling glasses as fuzzy crystals, capturing vibrational properties and the boson peak at low temperatures.

Findings

Density of states in acoustic branches flattens, leading to a boson peak.

Model agrees well with experimental data for a-GeO₂ and Ba₈Ga₁₆Sn₃₀ glasses.

The theory is valid up to about 10% of the Debye temperature.

Abstract

We construct a quantum mechanical model of perfectly isotropic amorphous solids as fuzzy crystals and establish an analytical theory of vibrations for glasses at low temperature. Our theoretical framework relies on the basic principle that the disorder in a glass is similar to the disorder in a classical fluid, while the latter is mathematically encoded by noncommutative coordinates in the Lagrange formulation of fluid mechanics. We find that the density of states in the acoustic branches flattens significantly, leading naturally to a boson peak in the specific heat as a manifestation of a van Hove singularity. The model is valid in the same range as Debye's theory, namely up to circa 10% of the Debye temperature. Within this range, we find an excellent agreement between the theoretical predictions and the experimental data for two typical glasses, a-GeO$_2$ and Ba$_{8}$Ga$_{16}$Sn$_{30}$-clathrate. Our model supports the conceptual understanding of the nature of the boson peak in glasses as a manifestation of the liquid-like disorder. At the same time, it provides a novel, mathematically simple framework for a unitary treatment of thermodynamical and transport properties of amorphous materials and a solid background for inserting further elements of complexity specific to particular glasses.