Change of chirality at magic angles of twisted bilayer graphene

5 pags., 4 figs.We derive a simple formula for the real-space chirality of twisted bilayer graphene that can be related to the cross product of its sheet currents. This quantity shows well-defined plateaus for the first remote band as a function of the gate voltage which are approximately quantized for commensurate twist angles. The zeroth plateau corresponds to the first magic angle where a sign change occurs due to an emergent C6 symmetry. Our observation offers a new definition of the magic angle based on a macroscopic observable which is accessible in typical transport experiments.This work has been supported by Spain’s MINECO under Grants No. FIS2017- 82260-P, No. PGC2018-096955-B-C42, and No. CEX2018- 000805-M as well as by the CSIC Research Platform on Quantum Technologies PTI-001. T.S. also acknowledges support from Spain’s “Salvador de Madariaga” program under Grant No. PRX19/00024 and from Germany’s Deutsche Forschungsgemeinschaft (DFG) via SFB 1277