Fig. 3: Lifshitz transition at the van Hove Singularity.
From: Experimental evidence of the topological obstruction in twisted bilayer graphene
a Full energy dependence of the experimental QPI signal, both in real (top row) and reciprocal space (bottom row). The scale bars are 10 nm and 1 nm−1, respectively. In all images, we have kept a constant tunneling resistance of 2 GΩ. b Calculated constant energy contours of the pristine (without defect and strain) TBG lowest energy bands across the Lifshitz transition. The colored arrows indicate the possible back-scattering processes that can be measured from the experiments of (a). c Same data unfolded to the original graphene valleys to explicit the intra-mini-valley scattering process represented by colored arrows. The twist angle has been increased for presentation purposes. d Energy dispersion of TBG reconstructed from the data of (a) (solid squares) and the corresponding images calculated by tight-binding (diamonds). The error bars correspond to the width of 2q-arcs. See Fig. S4 for these images. The colors of the square and diamond correspond to those of the scattering process depicted in (c). This scatter plot is overlaid on the electronic dispersion calculated by tight-binding with (yellow) or without (black) heterostrain. The colored arrows correspond to the scattering processes introduced in (b).
