Giant Faraday rotation due to excitation of magnetoplasmons in graphene microribbons

A single graphene sheet, when subjected to a perpendicular static magnetic field provides Faraday rotation that, per atomic layer, greatly surpasses that of any other known material. This Giant Faraday rotation originates from the cyclotron resonance of massless electrons, which allows dynamical tuning through either external electrostatic or magnetostatic setting. Furthermore, the rotation direction can be controlled by changing the sign of the carriers in graphene, which can be done by means of an external electric field. However, despite these tuning possibilities, the requirement of large magnetic fields hinders application of the Faraday effect in real devices, especially for frequencies higher than few THz. In this work we demonstrate that, for a given value of the static external magnetic field, giant Faraday rotation can be achieved in arrays of graphene microribbons at frequencies much higher than the corresponding cyclotron frequency. The main feature in the magneto-optical response of graphene ribbons is not associated with the cyclotron resonance but rather with the fundamental magnetoplasmon excitation of a single ribbon. The magnetoplasmon nature of Faraday rotation in graphene ribbons opens great possibilities, as the resonance frequency can be locally selected by appropriately choosing the width of the ribbon while still preserving the tuning capability through a (smaller) external magnetic field.