Fizika Nizkikh Temperatur: Volume 46, Number 2 (February 2020), p. 130-137 ( to contents , go back )
Are universal “anomalous” properties of glasses at low temperatures truly universal?
Laboratorio de Bajas Temperaturas, Departamento de Física de la Materia Condensada Universidad Autónoma de Madrid, Madrid, Spain
Condensed Matter Physics Center (IFIMAC) and Instituto Nicolás Cabrera (INC) Universidad Autónoma de Madrid, Madrid, Spain
Received October 29, 2019, published online December 27, 2019
The specific heat Cp and other properties of glasses (ranging from amorphous solids to disordered crystals) at low temperatures are well known to be markedly different from those in fully-ordered crystals. For decades, this qualitative, and even quantitative, universal behavior of glasses has been thoroughly studied. However, a clear understanding of its origin and microscopic nature, needless to say, a closed theory, is still lacking. To shed light on this matter, I review the situation in this work, mainly by compiling and discussing measured low-temperature Cp data of many glasses and disordered crystals, as well as highlighting a few exceptions to that “universality rule”. Thus, one can see that, in contrast to other low-temperature properties of glasses, the magnitude of the “glassy” Cp excess at low temperature is far from being universal. Even worse, some molecular crystals without a clear sign of disorder exhibit linear coefficients in Cp larger than those found in many amorphous solids, whereas a few of the latter show negligible values.
Key words: specific heat, low temperature, glasses, amorphous solids, tunneling states, boson peak.