Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session S48: Electrons, Phonons, Electron-Phonon Scattering, and Phononics V
8:00 AM–11:00 AM,
Thursday, March 17, 2022
Room: McCormick Place W-471A
Sponsoring
Units:
DCOMP DMP
Chair: Chris Marianetti, Columbia University
Abstract: S48.00010 : Topological Invariant of Acoustic Phonons in 2D materials*
10:12 AM–10:24 AM
Presenter:
Gunnar F Lange
(University of Cambridge)
Authors:
Gunnar F Lange
(University of Cambridge)
Adrien Bouhon
(NORDITA)
Bartomeu Monserrat
(University of Cambridge)
Robert-Jan Slager
(University of Cambridge)
2D materials that are allowed to flex out-of-plane display an unusual acoustic phonon mode – the flexural mode. This mode disperses quadratically away from the center of the Brillouin zone, as opposed to the linear dispersion of the in-plane modes. This leads to an unusual triple degeneracy at the zone center, with two linear and one quadratic band touching. This band touching is unusual because it is enforced by Goldstone’s theorem rather than symmetry, as will be discussed. I will also discuss the topological invariant associated with this crossing and how this invariant affects the physics. The invariant is a priori of quaternionic type, but it reduces to a Z2 invariant under rather general assumptions. This turns out to have important implications for the band splitting that occurs when a 2D material is grown on a substrate. This splitting will be discussed for the specific case of graphene, where the Z2 invariant associated with the acoustic bands turns out to be non-trivial.
*This work was supported by the Aker Scholarship, the Gianna Angelopoulos Programme for Science, Technology, and Innovation, the Winton Programme for the Physics of Sustainability, the Marie Skłodowska Curie Programme under EC Grant No.842901 and Trinity College at the University of Cambridge.
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