2019/12/29 by Lamparski, Michael, Van Troeye, Benoit, Meunier, Vincent · 1 citation
#FOS: Physical sciences #Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
paper · doi:10.48550/arxiv.1912.12568
The phonon spectra of twisted bilayer graphene (tBLG) are analyzed for a series of 692 twisting angle values in the [0,30°] 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 Γ point for the large moiré 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 θ\rm B∼ 3.75°.