▎ 摘　　要

Graphene, a two-dimensional carbon crystal with a gas of massless Dirac fermions, has promise as a material that is useful in photonic and optoelectronic devices. A comprehensive understanding of carrier cooling in photoexcited graphene is necessary for their applications, however, as competing cooling processes, electronphonon scattering, and supercollisions, complicate the problem. Specifically, in energy harvesting, supercollision promotes further carrier cooling and, therefore, leads to lower efficiency, placing doubt on the feasibility of device applications. Herewe present evidence of suppressed supercollisions in trilayer graphene on a SiC(000 (1) over bar) substrate by directly observing photoexcited carriers and numerically analyzing a phenomenological two-temperature model. Knowing that supercollisions restrict the capabilities of graphene-based devices, our results provide a breakthrough for improving their performance.