  So far, research in the field of metamaterials has been carried out largely
with arrays of flat, 2-dimensional structures. Here, we report a newly
identified magnetic resonance in Split Cylinder Resonators (SCRs), a
3-dimensional version of the Split Ring Resonator (SRR), which were fabricated
with the Proton Beam Writing technique. Experimental and numerical results
indicate a hitherto unobserved 3-dimensional resonance mode under normal
incidence at about 26 THz, when the SCR depth is approximately half the free
space wavelength. This mode is characterized by strong currents along the
cylinder axis which are concentrated at the cylinder gaps. Due to their
orientation, these axial currents give rise to a magnetic response under normal
incidence, which is not possible in shallow SRRs. Our results reveal new
behavior in the SRR structure which arises from a change in its aspect ratio.
Such new resonances can have a significant influence on the quest for
practical, 3-dimensional metamaterials.
