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

TL;DR

This study investigates low-temperature thermal properties of a minimally disordered crystal, revealing glassy anomalies caused by molecular reorientational freezing, which enhances understanding of universal glassy behaviors.

Contribution

It demonstrates that glassy anomalies can occur in crystals with minimal disorder due to molecular reorientational freezing, challenging previous notions about disorder requirements.

Findings

Glassy anomalies observed in a minimally disordered crystal.

Anomalies linked to freezing of molecular reorientational jumps.

Minimal disorder can induce glassy low-temperature properties.

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.