▎ 摘　　要

Understanding and controlling collective oscillations of electrons in graphene have enabled new classes of devices for deep subwavelength metamaterials, extraordinarily strong light-matter interactions, and nano-optoelectronic switches. Here, we demonstrate both theoretically and experimentally that the plasmon-plasmon and plasmon-radiation interactions modify strongly the plasmon resonance energy, radiative damping, and oscillator strength in graphene nanoribbon arrays. As the graphene filling factor approaches one, plasmon resonance energy becomes zero. And even for the moderate filling factors of about 50%, plasmon radiative lifetime reduces to a ps time scale. We find scaling of plasmons with respect to the graphene doping level and filling factor, which both control the strength of the radiative and long-range Coulomb interactions. The surprisingly large plasmon energy shift and radiative damping would significantly affect graphene-based plasmonic device performance.