THz spectroscopy of graphene coupled to LaAlO3/SrTiO3 nanoscale junctions*

We investigate the gate-dependent optical response of graphene using the broadband nonlinear generation and detection capabilities of nanoscale junctions created at the LaAlO3/SrTiO3 interface [1]. Using the large non-resonant third-order nonlinear susceptibility in SrTiO3, strong difference frequency mixing occurs when the junction is biased, leading to induced polarization that can also be detected at the junction [2]. Here we discuss results of gate-dependent experiments which interrogate the relationship between the THz signal and the gate location with respect to the Dirac point in devices where graphene is coupled to the LaAlO3/SrTiO3 interface. Preliminary results suggest we may be detecting a surface plasmon resonance or phonon mode. We will also discuss results indicating a gate-dependent enhancement of the graphene absorption.

[1] C. Cen, et al., Nature Materials 7, 298 (2008).
[2] Y. Ma, et al.,, Nano Lett 13, 2884 (2013).