Analogous vibrational features in other disordered materials

Determine whether vibrational features analogous to the anomalously large atomic root-mean-square fluctuations and their associated effects on heat transport observed in disordered silicon also occur in other disordered systems.

Background

The paper investigates amorphous, polycrystalline, and paracrystalline silicon using harmonic normal-mode analysis, finite-temperature molecular dynamics, and site-projected thermal conductivity. It identifies low-frequency “sloppy modes” and sites with unusually large root-mean-square atomic fluctuations, which generally correlate with locally suppressed heat transport.

The authors explicitly extend the significance of these silicon-specific observations through a conjecture concerning other disordered systems. The conjecture is unresolved because the study analyzes only silicon materials and does not test whether comparable vibrational behavior occurs in other amorphous or glassy materials.

References

The lattice dynamics of disordered systems (amorphous solids, polymers and glasses) are often distinct from crystalline analogues. Examples include the "two-level systems" and the Boson peak. Here, we show that even the venerable material amorphous silicon offers new wrinkles: (1) realistic networks studied with DFT-quality interatomic potentials show the existence of harmonic modes exhibiting anomalously large root-mean-square variation in atomic positions, and (2) these dynamics determine the processes of heat transport. We correlate the atomic dynamics with transport using the site-projected thermal conductivity [C. Ugwumadu et. al Phys. Status Solidi B 263, e202500316 (2026)], and conjecture that these observations are relevant to other disordered systems.

— Lattice dynamics of disordered phases of silicon and spatially resolved computations of thermal conductivity  (2610.10165 - Gautam et al., 7 Oct 2026) in Abstract