A twisted graphene bilayer consists of two graphene monolayers rotated by an angle θ with respect to each other. Theory predicts that charge-neutral twisted graphene bilayers display a drastic reduction of their Fermi velocity vF for 0θ20^∘ and 40θ60^∘. In this paper we present evidence for an additional anisotropic reduction of vF in the presence of external electrostatic fields. We also discuss in quantitative detail velocity renormalization for other relevant bands in the vicinity of the K point. Except for a rigid energy shift, electrostatic fields and doping by metal atoms give rise to similar renormalization of the band structure of twisted graphene bilayers.
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Xian et al. (2011) studied this question.