Fig. 1: Quasiparticle interference near a defect in TBG.
From: Experimental evidence of the topological obstruction in twisted bilayer graphene
a The Brillouin zones of the top (blue hexagon) and bottom layer (yellow hexagon) are rotated by the twist angle θ. This defines the two moiré mini-valleys (purple and green hexagons), which are folded on top of each other in the mini-Brillouin zone (black hexagon). In each mini-valley, the Dirac cones coming from different layers have the same chirality, indicated by the rotating arrows. b STM topograph of 4.3° TBG (Vb = 200 mV, it = 100 pA). A point defect is visible near the center of the image. The scale bar is 3 nm. The colored stars correspond to the locations of the spectroscopic measurements presented in Fig. 2a. c Larger field of view of the local density of states image around the point defect at the center of the image. The image was measured at the same tunneling conditions. The scale bar is 10 nm. The dashed square corresponds to the area of the image of (b). d Possible inter-cone back-scattering within mini-valley + (top). Expected FFT of the top layer QPI signal for Dirac cones of the same (center) or opposite (bottom) chirality. e The position of the observed defect is identified by the red dot and labeled D. The position of other defects studied in Fig. 2 is marked by dots of other colors. f Modulus of the Fast Fourier Transform of the image in (c). The reciprocal lattice vectors G1 and G2 of the moiré are indicated, and the mBz is shown in orange. The scale bar is 1 nm−1.
