2014/07/23 by Tomás Pérez-Castañeda, Cristian Rodríguez-Tinoco, Javier Rodríguez-Viejo +1
Physics and Astronomy · #cond-mat.dis-nn #cond-mat.mtrl-sci #cond-mat.soft
paper · pdf · doi:10.1073/pnas.1405545111
24 pages, 5 figures, Proceedings of the National Academy of Sciences of the United States of America 07/2014
arxiv created 2014/07/23 · arxiv updated 2014/07/25
Glasses and other non-crystalline solids exhibit thermal and acoustic properties at low temperatures anomalously different from those found in crystalline solids, and with a remarkable degree of universality. Below a few K, these universal properties have been successfully interpreted using the Tunneling Model, which has enjoyed (almost) unanimous recognition for decades. Here we present low-temperature specific-heat measurements of ultrastable glasses of indomethacin that clearly show the disappearance of the ubiquitous linear contribution traditionally ascribed to the existence of tunneling two-level systems (TLS). When the ultrastable thin-film sample is thermally converted into a conventional glass, the material recovers a typical amount of TLS. This remarkable suppression of the TLS found in ultrastable glasses of indomethacin is argued to be due to their particular anisotropic and layered character, which strongly influences the dynamical network and may hinder isotropic interactions among low-energy defects, rather than to the thermodynamic stabilization itself. This explanation may lend support to the criticisms by Leggett and others to the standard Tunneling Model, although more experiments in different kinds of ultrastable glasses are needed to ascertain this hypothesis.