Realistic Tunneling States for the Magnetic Effects in Non-Metallic Real Glasses

TL;DR

This paper extends the standard tunneling model for glasses to include three-welled potentials, explaining magnetic effects in non-metallic glasses through localized atomistic tunneling states and inhomogeneities.

Contribution

It provides a cellular atomic structure model justifying three-welled potentials and explains magnetic phenomena via localized tunneling states and TWPs in glasses.

Findings

Magnetic effects explained by localized tunneling states and TWPs.

The cellular model supports the existence of three-welled potentials.

Strategies for atomistic simulations of tunneling states are discussed.

Abstract

The discovery of magnetic and compositional effects in the low temperature properties of multi-component glasses has prompted the need to extend the standard two-level systems (2LSs) tunneling model. A possible extension \cite{Jug2004} assumes that a subset of tunneling quasi-particles is moving in a three-welled potential (TWP) associated with the ubiquitous inhomogeneities of the disordered atomic structure of the glass. We show that within an alternative, cellular description of the intermediate-range atomic structure of glasses the tunneling TWP can be fully justified. We then review how the experimentally discovered magnetic effects can be explained within the approach where only localized atomistic tunneling 2LSs and quasi-particles tunneling in TWPs are allowed. We discuss the origin of the magnetic effects in the heat capacity, dielectric constant (real and imaginary parts), polarization echo and SQUID magnetization in several glassy systems. We conclude by commenting on a strategy to reveal the mentioned tunneling states (2LSs and TWPs) by means of atomistic computer simulations and discuss the microscopic nature of the tunneling states in the context of the potential energy landscape of glass-forming systems.