Terahertz ratchet in graphene two-dimensional metamaterial formed by a patterned gate with an antidot array

Photocurrents are generated by the ratchet effect -- the combined action of a spatially periodic in-plane electrostatic potential and a periodically modulated radiation electric field caused by near-field diffraction. Polarized radiation is converted into a direct current due to the spatial asymmetry of the metamaterial. The ratchet current vector is gate tunable via a global back gate and a patterned gate, which control the lateral asymmetry of the system.