Ultrafast Optical Response of Graphene/$LaAlO_3/SrTiO_3$ Heterostructure

Graphene is a promising tunable plasmonic material in the terahertz regime. Plasmons can be induced in graphene by femtosecond laser excitation, and their resonance frequency can be gate-tuned over a broad terahertz range\footnote{L. Ju, \textit{et al.}, Nature Nanotech. \textbf{6}, 630 (2011)}. Another 2D electron system, the complex-oxide heterostructure LaAlO$_3$/SrTiO$_3$, has been shown to exhibit great promise for control and detection of broadband THz emission at extreme nanoscale dimensions\footnote{Y. Ma, \textit{et al.}, Nano Lett. \textbf{13}, 2884 (2013)}. Recently, we have successfully integrated these two platforms: we have created graphene/LaAlO$_3$/SrTiO$_3$ structures with high mobility in the graphene channel and oxide nanostructures directly underneath the graphene layer. Here we describe new experiments that probe graphene plasmonic behavior using this nanoscale THz spectrometer. This unprecedented control of THz radiation at 10 nm length scales creates a pathway toward hybrid THz functionality in graphene/LaAlO$_3$/SrTiO$_3$ heterostructures.