Are universal “anomalous” properties of glasses at low temperatures truly universal?

Abstract

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 lowtemperature 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.

Emergence of two-level systems in glass formers: a kinetic Monte Carlo study

“…Figure 1 plots C v from Eqs. ( 1) and (10). We observed an excellent agreement with simulations for c 1 and c 3 at T I 0.10 and 0.05 respectively.…”

“…(a) Dashed lines and (b) short dashed lines show theoretical values from Eqs. (1) and(10), which are accurate for TI 0.05. For TI 0.06, Eq.…”

“…Their theory has successfully explained a plethora of low-T thermal and acoustic properties of glasses [6]. Nevertheless, the microscopic nature of TLS and their possible universal properties remain controversial [7][8][9][10][11]. Recently, TLS in glasses have attracted additional interest due to their strong relevance to noise in quantum computing devices [12].…”

“…At T 10K, the heat capacity of many glasses follows c 1 T +(c D +c 3 )T 3 [3,10]. The linear term c 1 T dominates at T 1K and is explained by the TLS theory [4,5].…”

A new paradigm for the low-T glassy-like thermal properties of solids

“…In addition to this questionable confidence and theoretical confusion, the "anomalous" nature of glassy features in solids is in deep crisis [12]. This is because the same allegedly "anomalous" features have been systematically observed in non-disordered systems, atomic and molecular cryocrystals [13][14][15] and in quasicrystals/incommensurate structures [16].…”