ArXiv · 2026
We report a photocurrent studies of a magic angle twisted bilayer graphene device using near infrared light. Through photocurrent imaging and polarization dependence, we separate the photo-thermoelectric effect from the photogalvanic effect. We observe a circular photogalvanic effect (CPGE) over a wide range of doping and temperature. The CPGE at normal incidence constraints the symmetry of the system to C₁, and points to a Berry curvature dipole, in agreement with theoretical predictions for strained graphene. Remarkably, the CPGE vanishes for filling -2.5 < ν < -1.5, suggesting an additional symmetry breaking in that regime. Insight into this effect is obtained through Berry curvature dipole calculations, which emphasize a novel symmetry breaking effect near ν=-2.
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