Fig. 1: Directional photocurrents in symmetry-broken optoelectronic metasurfaces.
a, Illustration of an optoelectronic metasurface consisting of symmetry-broken gold nanoantennas on graphene. Femtosecond laser illumination stimulates vectorial photocurrents and consequent emission of ultrafast THz pulses. b, Measured (solid line) and simulated (solid fill) transmission spectra for two nanoantenna designs with resonances at 800 nm (blue) and 1,550 nm (orange). c, Measured incident-wavelength-dependent THz field amplitude (solid lines with data markers) and d.c. photocurrent (dashed line), as well as simulated field intensity (solid fills). Top insets: scanning electron micrographs of the fabricated nanoantenna elements. Bottom insets: simulated plasmonic-field enhancements. Scale bars, 200 nm. d, Measured THz time-domain signals emitted from the resonantly excited 800-nm (left) and 1,550-nm (right) metasurfaces, compared with those from 1-mm-thick ZnTe. Curves are offset for clarity. Inset: amplitude spectra (plotted on a logarithmic scale) revealing bandwidth out to 3 THz, limited by phase matching in the 1-mm ZnTe detection crystal. e, Incident-fluence-dependent THz field amplitude and d.c. photocurrent readout, along with a linear fit to low fluence (solid fill). a.u., arbitrary units.
