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arXiv · 2303.02173

Flat-band optical phonons in twisted bilayer graphene

Emmanuele Cappelluti·Jose Angel Silva-Guillén·Habib Rostami·Francisco Guinea
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Abstract

Twisting bilayer sheets of graphene have been proven to be an efficient way to manipulate the electronic Dirac-like properties, resulting in flat bands at magic angles. Inspired by the electronic model, we develop a continuum model for the lattice dynamics of twisted bilayer graphene and we show that a remarkable band flattening applies to almost all the high-frequency in-plane lattice vibration modes, including the valley Dirac phonon, valley optical phonon, and zone-center optical phonon bands. Utilizing an approximate approach, we estimate small but finite magic angles at which a vanishing phonon bandwidth is expected. In contrast to the electronic case, the existence of a restoring potential prohibits the emergence of a magic angle in a more accurate modeling. The predicted phonon band-flattening is highly tunable by the twist angle and this strong dependence is directly accessible by spectroscopic tools.

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Emmanuele Cappelluti, Jose Angel Silva-Guillén, Habib Rostami, Francisco Guinea. 2023-03-03. Flat-band optical phonons in twisted bilayer graphene. https://doi.org/10.1103/physrevb.108.125401

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