Layers of twisted bilayer graphene exhibit varieties of exotic quantum phenomena1-5. Today, the twist angle {Theta} has become an important degree of freedom for exploring novel states of matters, i.e. two-dimensional superconductivity ( {Theta} = 1.1{deg})6, 7 and a two-dimensional quasicrystal ({Theta} = 30{deg})8, 9. We report herein experimental observation on the photo-induced ultrafast dynamics of Dirac fermions in the quasicrystalline 30{deg} twisted bilayer graphene (QCTBG). We discover that hot carriers are asymmetrically distributed between the two graphene layers, followed by the opposing femtosecond relaxations, by using time- and angle-resolved photoemission spectroscopy. The key mechanism involves the differing carrier transport between layers and the transient doping from the substrate interface. The ultrafast dynamics scheme continues after the Umklapp scattering, which is induced by the incommensurate interlayer stacking of the quasi-crystallinity. The dynamics in the atomic layer opens the possibility of new applications and creates interdisciplinary links in the optoelectronics of van der Waals crystals.
Download