Tunable circular dichroism in a graphene extrinsically chiral L-shaped metasurface

In this manuscript, we propose a graphene metasurface composed of an L-shaped pattern to achieve a tunable circular dichroism under oblique incidence in the mid-infrared region. For our graphene extrinsically 3D-chiral structure, there are two graphene localized surface plasmons resonant modes at the wavelength of 11.05 and 16.69 mu m. A broad bandwidth circular dichroism between the two modes is generated, so are two bands of negative circular dichroism (circular dichroism is minus). The circular dichroism can be enhanced by increasing the incident angle. Maximal circular dichroism can reach 24.64% when the incident angle is 60 degrees. The mechanism of circular dichroism generation is attributed to the strong interaction between electric and magnetic dipoles. Besides, the circular dichroism can be tuned by changing the Fermi energy and is affected by the intrinsic relaxation time. It will have a wide application in photonic devices, which can promote the development of analytical chemistry and numerous other areas.