  The design of artificial nonlinear materials requires control over the
internal resonant charge densities and local electric field distributions. We
present a MM design with a structurally controllable oscillator strength and
local electric field enhancement at terahertz frequencies. The MM consists of a
split ring resonator (SRR) array stacked above an array of nonresonant closed
conducting rings. An in-plane, lateral shift of a half unit cell between the
SRR and closed ring arrays results in a decrease of the MM oscillator strength
by a factor of 4 and a 40% change in the amplitude of the resonant electric
field enhancement in the SRR capacitive gap. We use terahertz time-domain
spectroscopy and numerical simulations to confirm our results and we propose a
qualitative inductive coupling model to explain the observed electromagnetic
reponse.
