  All-optical active plasmonic devices are of fundamental importance for
designing efficient nanophotonic circuits. We theoretically propose and
numerically investigate an active plasmonic device made up of a nonlinear
epsilon-near-zero metamaterial slab of thickness smaller than 100 nanometers
lying on a linear epsilon-near-zero metamaterial substrate. We predict that, in
free-space coupling configuration, the device, operating at low-intensity,
would display plasmon mediated hysteresis behavior since the phase difference
between the reflected and the incident optical waves turns out to be
multi-valued and dependent on the history of the excitation process. Such an
hysteresis behavior would allow to regard the proposed device as a compact
memory unit whose state is accessible by measuring either the mentioned phase
difference or the power, which is multi-valued as well, carried by the
nonlinear plasmon wave. Since multiple plasmon powers comprise both positive
and negative values, the device would also operate as a switch of the plasmon
power direction at each jump along an hysteresis loop.
