Realistic tunnelling states for the magnetic effects in non-metallic real glasses

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) tunnelling model. A possible extension assumes that a subset of tunnelling 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 tunnelling TWP can be fully justified. We then review how the experimentally discovered magnetic effects can be explained within the approach where only localized atomistic tunnelling 2LSs and quasi-particles tunnelling 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 tunnelling states (2LSs and TWPs) by means of atomistic computer simulations and discuss the microscopic nature of the tunnelling states in the context of the potential energy landscape of glass-forming systems

Keywords:

• amorphous solids
• atomic structure
• cellular structures
• glass
• granular materials
• quantum mechanical calculation
• low-temperature physics
• magnetic effects in non-magnetic glasses

Acknowledgements

One of us (SB) acknowledges support from the Italian Ministry of Education, University and Research (MIUR) through a Ph.D. Grant of the Progetto Giovani (ambito indagine n.7: materiali avanzati (in particolare ceramici) per applicazioni strutturali), as well as from the Bando VINCI-2014 of the Università Italo-Francese. We are very grateful to Maksym Paliienko for his help with data fitting and manuscripts preparation. GJ gratefully acknowledges stimulating discussions with A.S. Bakai.

Notes

No potential conflict of interest was reported by the authors.