Abstract
We have studied the electronic and optical properties of twisted bilayer graphene using the first-principles GW-Bethe-Salpeter equation approach. The optical absorption spectrum of twisted-bilayer graphene is analogous to that of graphene, which is attributed to the characteristic dispersion of Dirac fermions and is contrary to the Bernal-stacking bilayer graphene. Many-electron effects play a pivotal role in the optical spectrum and quasiparticle excitations, which yield an enhanced excitonic resonance and an induced renormalization of the Fermi velocity for twisted bilayer graphene. Our results indicate that it is necessary to consider electron-electron and electron-hole interactions simultaneously for describing the corresponding many-electron effects.