Tunable Graphene Split-Ring Resonators

A split-ring resonator is a prototype of meta-atom in metamaterials. Though\nnoble metal-based split-ring resonators have been extensively studied, up to\ndate, there is no experimental demonstration of split-ring resonators made from\ngraphene, an emerging intriguing plasmonic material. Here, we experimentally\ndemonstrate graphene split-ring resonators with deep subwavelength (about one\nhundredth of the excitation wavelength) magnetic dipole response in the\nterahertz regime. Meanwhile, the quadrupole and electric dipole are\nobserved,depending on the incident light polarization. All modes can be tuned\nvia chemical doping or stacking multiple graphene layers. The strong\ninteraction with surface polar phonons of the SiO2 substrate also significantly\nmodifies the response. Finite-element frequency domain simulations nicely\nreproduce experimental results. Our study moves one stride forward toward the\nmulti-functional graphene metamaterials, beyond simple graphene ribbon or disk\narrays with electrical dipole resonances only.\n