Nanoscale Directional Photocurrents with Symmetry-Broken Optoelectronic Metasurfaces

Light-driven electrical currents are of great importance in information science and microelectronics, particularly in emerging topological, magnetic, and low-dimensional materials, which introduce new speed limits and light-based control degrees of freedom. However, such photocurrents typically rely on the broken spatial or temporal symmetries, thus either intrinsic to the lattice and constrained to specific light-matter interaction geometries, or dependent upon applied static fields that are difficult to texture on small spatial scales. Artificially structured plasmonic systems can be utilized to overcome these spatial limitations and concentrate light down into deeply sub-diffractive nanometer scales. In this work, we show that hybrid plasmonic metasurface systems offer much broader capabilities for harnessing charge flows at previously inaccessible spatial scales. Nanoscale directional photocurrents in these systems are a universal manifestation of broken inversion symmetry, with patterned gold resonators on graphene serving as a testbed system. The rapidly-evolving nanoscale dynamics across the coupled photonic, electronic, and thermal responses introduces net photothermoelectric currents that are sensitive to the local symmetry of the light-matter interaction. The local (nanoscale) and global (millimeter-scale) photocurrents are highly responsive to the polarization and frequency of the ultrafast light pulses, leading to a combination of designer patterning and active control over ultrafast, nanoscale vectorial currents. As an immediate application, we exploit this scheme for efficient and versatile generation of broadband ultrafast terahertz radiation and terahertz vector beams.