Ultrafast photoresponse of oxide nanostructures

Photoconductivity has been demonstrated for nanostructures at the interface of LaAlO$_3$/SrTiO$_3$ and spectral response shows signatures of in-gap states being responsible for photoresponse\footnote{Irvin, P. et al. Rewritable Nanoscale Oxide Photodetector. Nature Photon. 4, 849-852 (2010).}. However, as a wide bandgap material, SrTiO$_3$ shows large nonlinear optical coefficients. Here we discuss time-resolved measurements for exploring the nonlinearity of photoconductivity in the oxide nanostructures. It is found that a nonresonant $\chi^{(3)}$ process results in the observed tunable localized ultrafast response, as well as optical rectification, which can principally lead to the generation and detection of THz radiation. Due to the nanoscale nature of our device, these results foreshadow the control of THz field at single molecule scales.