▎ 摘　　要

Non-Abelian gauge potentials are quite relevant in subatomic physics, but they are relatively rare in a condensed matter context. Here we report the experimental evidence for non-Abelian gauge potentials in twisted graphene bilayers by scanning tunneling microscopy and spectroscopy. At a magic twisted angle, theta approximate to (1.11 +/- 0.05)degrees, a pronounced sharp peak, which arises from the nondispersive flat bands at the charge neutrality point, is observed in the tunneling density of states due to the action of the non-Abelian gauge fields. Moreover, we observe confined electronic states in the twisted bilayer, as manifested by regularly spaced tunneling peaks with energy spacing delta E approximate to v(F)/D approximate to 70 meV (here v(F) is the Fermi velocity of graphene and D is the period of the moire patterns). This indicates that the non-Abelian gauge potentials in twisted graphene bilayers confine low-energy electrons into a triangular array of quantum dots following the modulation of the moire patterns. Our results also directly demonstrate that the Fermi velocity in twisted bilayers can be tuned from about 10(6) m/s to zero by simply reducing the twisted angle of about 2 degrees.