  Ultrafast photon-assisted tunneling is shown to lead to large nonlinear
dynamic currents that can be used to generate dc rectified current as well as
higher order harmonic response from a metasurface-coupled tunnel diode. This
artificial nonlinear media can have tailored resonances in the infrared around
the longitudinal optical phonon modes of various compatible restrahlen oxides
leading to enhanced electric field confinement in a metal-oxide-semiconductor
tunnel diode. This provides a new avenue for the examination and design of
nonlinear phenomena extending the concept of nonlinear susceptibility to
nonlinear conductance and the dynamic current in these devices.
