Tunable terahertz toroidal response by graphene metamaterials

We present the toroidal dipolar response in graphene-based disk metamaterials at terahertz range and find that this response has a dominant role over other multipoles as compared with that in noble metals, attributed to the atom-level ultrathin characteristic of two-dimensional graphene. Moreover, the toroidal response is tunable with the Fermi level of graphene, which is readily to be realized by applying electrostatic gating, photo-injection, etc. In addition, layers of graphene also obviously influence the toroidal response in terms of the resonant frequency and magnitude. It is believed that the actively tunable characteristic of terahertz toroidal response in graphene metamaterials, in contrast to noble-metal-based metastructures, can provide unique convenience for further exploration of toroidal dipolar response.