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arXiv · 1912.12568

Soliton signature in the phonon spectrum of twisted bilayer graphene

Michael Lamparski·Benoit Van Troeye·Vincent Meunier
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Abstract

The phonon spectra of twisted bilayer graphene (tBLG) are analyzed for a series of 692 twisting angle values in the $[0,30{\degree}]$ range. The evolution of the phonon bandstructure as a function of twist angle is examined using a band unfolding scheme where the large number of phonon modes computed at the $\Gamma$ point for the large moir\'e tBLG supercells are unfolded onto the Brillouin Zone (BZ) of one of the two constituent layers. In addition to changes to the low-frequency breathing and shear modes, a series of well-defined side-bands around high-symmetry points of the extended BZ emerge due to the twist angle-dependent structural relaxation. The results are rationalized by introducing a nearly-free-phonon model that highlights the central role played by solitons in the description of the new phonon branches, which are particularly pronounced for structures with small twist angles, below a buckling angle $\theta_{\rm B}\sim {3.75}{\degree}$.

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Michael Lamparski, Benoit Van Troeye, Vincent Meunier. 2019-12-29. Soliton signature in the phonon spectrum of twisted bilayer graphene. https://arxiv.org/abs/1912.12568

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