The universality of the density of states of low-energy excitations in glasses

Abstract

Amorphous solids exhibit a variety of unusual low-temperature properties. These so-called ‘anomalies’ can be described by a phenomenological model based on the assumption that small structural entities are capable of tunnelling between different sites in the random structure. The validity and limitations of this model are discussed on the basis of new experimental results, focusing on the influence of glass-transition temperature, sample preparation and superconductivity on the density of tunnelling states.