Electrodynamics of Amorphous Media at Low Temperatures

TL;DR

This paper explains the microscopic origin of electric dipole moments in low-temperature amorphous solids, linking structural transitions to dielectric properties and their anomalies, with implications for understanding glassy and partially crystalline materials.

Contribution

It provides a microscopic explanation for the electric dipole moments of two-level systems in amorphous solids, connecting polarization fluctuations to experimental observations.

Findings

Dipole moments arise from polarization fluctuations between local configurations.

Estimated dipole magnitudes are consistent with experimental data.

Dipole interactions significantly influence the Grüneisen parameter anomaly.

Abstract

Amorphous solids exhibit intrinsic, local structural transitions, that give rise to the well known quantum-mechanical two-level systems at low temperatures. We explain the microscopic origin of the electric dipole moment of these two-level systems: The dipole emerges as a result of polarization fluctuations between near degenerate local configurations, which have nearly frozen in at the glass transition. An estimate of the dipole's magnitude, based on the random first order transition theory, is obtained and is found to be consistent with experiment. The interaction between the dipoles is estimated and is shown to contribute significantly to the Gr\"{u}neisen parameter anomaly in low $T$ glasses. In completely amorphous media, the dipole moments are expected to be modest in size despite their collective origin. In partially crystalline materials, however, very large dipoles may arise, possibly explaining the findings of Bauer and Kador, J. Chem. Phys. {\bf 118}, 9069 (2003).