Non-phononic density of states of two-dimensional glasses revealed by random pinning

Kumpei Shiraishi; Hideyuki Mizuno; Atsushi Ikeda

doi:10.1063/5.0142648

Non-phononic density of states of two-dimensional glasses revealed by random pinning

J Chem Phys. 2023 May 7;158(17):174502. doi: 10.1063/5.0142648.

Authors

Kumpei Shiraishi^{1

2}, Hideyuki Mizuno¹, Atsushi Ikeda^{1

3}

Affiliations

¹ Graduate School of Arts and Sciences, University of Tokyo, Komaba, Tokyo 153-8902, Japan.
² Laboratoire Charles Coulomb (L2C), Université de Montpellier, CNRS, 34095 Montpellier, France.
³ Research Center for Complex Systems Biology, Universal Biology Institute, University of Tokyo, Komaba, Tokyo 153-8902, Japan.

PMID: 37125708
DOI: 10.1063/5.0142648

Abstract

The vibrational density of states of glasses is considerably different from that of crystals. In particular, there exist spatially localized vibrational modes in glasses. The density of states of these non-phononic modes has been observed to follow g(ω) ∝ ω4, where ω is the frequency. However, in two-dimensional systems, the abundance of phonons makes it difficult to accurately determine this non-phononic density of states because they are strongly coupled to non-phononic modes and yield strong system-size and preparation-protocol dependencies. In this article, we utilize the random pinning method to suppress phonons and disentangle their coupling with non-phononic modes and successfully calculate their density of states as g(ω) ∝ ω4. We also study their localization properties and confirm that low-frequency non-phononic modes in pinned systems are truly localized without far-field contributions. We finally discuss the excess density of states over the Debye value that results from the hybridization of phonons and non-phononic modes.