Glassy anomalies in the low-temperature thermal properties of a minimally disordered crystalline solid

Abstract

The low-temperature thermal and transport properties of an unusual kind of crystal exhibiting minimal molecular positional and tilting disorder have been measured. The material, namely, low-dimensional, highly anisotropic pentachloronitrobenzene (PCNB) has a layered structure of rhombohedral parallel planes in which the molecules execute large-amplitude in-plane as well as concurrent out-of-plane librational motions. Our study reveals that low-temperature glassy anomalies can be found in a system with minimal disorder due to the freezing of (mostly in-plane) reorientational jumps of molecules between equivalent crystallographic positions with partial site occupation. Our findings will pave the way to a deeper understanding of the origin of above-mentioned universal glassy properties at low temperature.

12 pages, 4 figures

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• Jamming Criticality of Near-Crystals
• Specific heat at low temperatures in quasiplanar molecular crystals: Where do glassy anomalies in minimally disordered crystals come from?
• Physics of Phonon-Polaritons in Amorphous Materials
• Secondary relaxation in the terahertz range in 2-adamantanone from theory and experiments