▎ 摘　　要

High resolution TrARPES measurements of Kekule-ordered graphene resolve the dynamical evolution of electron-phonon interaction in the time domain and reveal the role of specific phonon modes in the ultrafast relaxation dynamics. Electron-phonon interaction and related self-energy are fundamental to both the equilibrium properties and non-equilibrium relaxation dynamics of solids. Although electron-phonon interaction has been suggested by various time-resolved measurements to be important for the relaxation dynamics of graphene, the lack of energy- and momentum-resolved self-energy dynamics prohibits direct identification of the role of specific phonon modes in the relaxation dynamics. Here, by performing time- and angle-resolved photoemission spectroscopy measurements on Kekule-ordered graphene with folded Dirac cones at the Gamma point, we have succeeded in resolving the self-energy effect induced by the coupling of electrons to two phonons at omega(1) = 177 meV and omega(2) = 54 meV, and revealing its dynamical change in the time domain. Moreover, these strongly coupled phonons define energy thresholds, which separate the hierarchical relaxation dynamics from ultrafast, fast to slow, thereby providing direct experimental evidence for the dominant role of mode-specific phonons in the relaxation dynamics.