Degradation of Phonons in Disordered Moiré Superlattices

Journal Article · 08 February 2022 · Physical Review Letters

DOI: https://doi.org/10.1103/physrevlett.128.065901 · OSTI ID:1961323

Ochoa, Héctor  ^[1]; Fernandes, Rafael M. ^[2]

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1. Donostia International Physics Center, Sebastian (Spain); IKERBASQUE, Basque Foundation for Science, Bilbao (Spain); Columbia Univ., New York, NY (United States); University of Minnesota
2. Univ. of Minnesota, Minneapolis, MN (United States)

The elastic collective modes of a moiré superlattice arise not from vibrations of a rigid crystal but from the relative displacement between the constituent layers. Despite their similarity to acoustic phonons, these modes, called phasons, are not protected by any conservation law. Furthermore, we show that disorder in the relative orientation between the layers and thermal fluctuations associated with their sliding motion degrade the propagation of sound in the moiré superlattice. Specifically, the phason modes become overdamped at low energies and acquire a finite gap, which displays a universal dependence on the twist-angle variance. Thus, twist-angle inhomogeneity is manifested not only in the non-interacting electronic structure of moiré systems, but also in their phonon-like modes. More broadly, our results have important implications for the electronic properties of twisted moiré systems that are sensitive to the electron-phonon coupling.

• Research Organization: Univ. of Minnesota, Minneapolis, MN (United States)
• Sponsoring Organization: NSF MRSEC; USDOE Office of Science (SC), Basic Energy Sciences (BES). Materials Sciences & Engineering Division
• Grant/Contract Number: SC0020045
• OSTI ID: 1961323
• Journal Information: Physical Review Letters, Journal Name: Physical Review Letters Journal Issue: 6 Vol. 128; ISSN 0031-9007
• Publisher: American Physical Society (APS)Copyright Statement
• Country of Publication: United States
• Language: English