Excitonic effects in twisted bilayer graphene
Abstract
In the present work, we consider the excitonic effects in the twisted bilayer graphene (tBLG) within the rotated bilayer Hubbard model. Both, intralayer and interlayer Coulomb interactions have been considered and the halffilling condition is imposed for the electronic densities is both layers of the bilayer. We calculate the excitonic gap parameter and the chemical potential for different twist angles and different values of the interlayer Coulomb interaction parameter. Furthermore, we show the appearance of the electronic flat bands in the electronic band structure, mediated by the excitonic effects. We show that there is a doubling effect of the Dirac's Kpoint at the low interaction limit and one of Dirac's nodes is stable and the other one changes its position as a function of rotation angle. At the large twist angle limit, there appear two additional Diraclike nodes at the Mpoint in the Brillouin zone. We show the excitonic redshift effect of the principal Dirac's point K, in the low interaction limit, while, at the strong interactions, we get also the blueshift effect at the Mpoint. Apart from the mentioned effects, the theory evaluated here predicts a metalsemiconductor transition in the tBLG system when augmenting the interlayer Coulomb interaction parameter.
 Publication:

Physica E LowDimensional Systems and Nanostructures
 Pub Date:
 January 2020
 DOI:
 10.1016/j.physe.2019.113682
 Bibcode:
 2020PhyE..11513682A