  To realize efficient nonlinear metamaterials, we investigate a method for
enhancing the local electric field in a metamolecule composed of two
radiatively coupled cut-wire resonators where resonance of the cut-wire
resonators and low-group-velocity propagation of an incident electromagnetic
wave simultaneously occur. Numerical analysis shows that the local electric
field in the metamolecule can be enhanced by decreasing the electrode size and
the gap of the capacitor structure of the cut-wire resonators while keeping the
equivalent electrical circuit parameters of the metamolecule constant. We
measure and compare the threshold incident power for a gas discharge in the
metamolecule fabricated in our previous study and that in the metamolecule with
shrunken capacitor structures. The experiment reveals that shrinking the
capacitor structure while keeping the resonance frequency of the metamolecule
decreases the threshold incident power for a gas discharge and may increase the
gas pressure where the threshold incident power is minimum. Further development
of this work will enable us to realize efficient nonlinear metamaterials that
have atmospheric-pressure gas as a nonlinear element.
