Microscopic description of the low-temperature anomalies in silica and lithium silicate via computer simulations

TL;DR

This study uses computer simulations to explore the potential energy landscape of silica and lithium silicate glasses, revealing the nature and properties of tunneling systems responsible for low-temperature anomalies.

Contribution

It systematically characterizes different types of double-well potentials and estimates the number of tunneling systems, providing a semi-quantitative match with experimental data.

Findings

Identification of three types of DWP related to different defect structures.

Detailed characterization of DWP properties like spatial extension and dipole moment.

Semi-quantitative agreement with dielectric, specific heat, and acoustic experiments.

Abstract

Information about the nature of the low-temperature anomalies and in particular the properties of the tunneling systems in silica and lithium silica glasses are revealed via computer simulations. The potential energy landscape of these systems is systematically explored for adjacent pairs of local minima which may act as double-well potentials (DWP) at low temperatures. Three different types of DWP are distinguished, related to perfectly coordinated silica, intrinsic silica defects, and extrinsic defects. Their properties like the spatial extension and the dipole moment are characterized in detail. Furthermore, the absolute number of tunneling systems, i.e. symmetric DWP, is estimated. The results are compared with dielectric echo, specific heat and acoustic experiments on Suprasil I and Suprasil W. A semi-quantitative agreement for all relevant features is obtained.