THz rectified optical response of LaAlO$_{3}$/SrTiO$_{3}$ nanojunctions

Conducting AFM lithography can be used to create a variety of nanoscale devices at the LaAlO$_{3}$/SrTiO$_{3}$ interface\footnote{C.Cen et al., Nature Material, \textbf{7}, 298 (2008)}\footnote{C.Cen et al., Science, \textbf{323}, 1026 (2009)}. Nanoscale junctions have been shown to exhibit strongly localized photoconductivity over a range of wavelengths spanning the visible and near-infrared regime\footnote{P.Irvin et al., Nature Photonics, \textbf{4}, 849 (2010)}. Power-dependent and interferometric measurements of these nanostructures with ultrafast laser pulses reveal a nonlinear photoconductive response attributed to second-order nonlinear susceptibility of SrTiO$_{3}$. The breaking of inversion symmetry comes from the strong local electric field that extends across the junction. The ultrafast response of these nanojunctions make them attractive candidates for generation and detection of THz radiation at molecular scales. This work is supported by NSF DMR-1104191.