Plasmons describe collective oscillations of electrons. They have a fundamental role in the dynamic responses of electron systems and form the basis of research into optical metamaterials^1,2,3. Plasmons of two-dimensional massless electrons, as present in graphene, show unusual behaviour^4,5,6,7 that enables new tunable plasmonic metamaterials^8,9,10 and, potentially, optoelectronic applications in the terahertz frequency range^8,9,11,12. Here we explore plasmon excitations in engineered graphene micro-ribbon arrays. We demonstrate that graphene plasmon resonances can be tuned over a broad terahertz frequency range by changing micro-ribbon width and in situ electrostatic doping. The ribbon width and carrier doping dependences of graphene plasmon frequency demonstrate power-law behaviour characteristic of two-dimensional massless Dirac electrons^4,5,6. The plasmon resonances have remarkably large oscillator strengths, resulting in prominent room-temperature optical absorption peaks. In comparison, plasmon absorption in a conventional two-dimensional electron gas was observed only at 4.2 K (refs 13, 14). The results represent a first look at light–plasmon coupling in graphene and point to potential graphene-based terahertz metamaterials.

等离子体描述了电子的集体振荡。它们在电子系统的动态响应中具有重要作用，并构成了对光学超材料^1,2,3研究的基础。二维无质量电子的等离子激元，如石墨烯中存在的，表现出不寻常的行为^4,5,6,7，使新的可调等离子体超材料^8,9,10和潜在的太赫兹频率范围内的光电应用成为可能^{8,9,11 ,12}。在这里，我们探索工程石墨烯微带阵列中的等离子体激发。我们证明了石墨烯等离子体共振可以通过改变微带宽度和原位在很宽的太赫兹频率范围内进行调谐静电掺杂。石墨烯等离子体频率的带宽度和载流子掺杂依赖性证明了二维无质量狄拉克电子^{4,5,6 的}幂律行为特征。等离子体共振具有非常大的振荡器强度，导致显着的室温光吸收峰。相比之下，传统二维电子气中的等离子体吸收仅在 4.2 K 处观察到（参考文献 13、14）。结果代表了对石墨烯中光-等离子体耦合的首次观察，并指出了潜在的基于石墨烯的太赫兹超材料。