  Electromagnetic metamaterials are man-made structures that have novel
properties such as a negative refraction index, not attainable in naturally
occurring materials. Although negative index materials (NIMs) in microwave
frequencies were demonstrated in 2001, it has remained challenging to design
NIMs for optical frequencies especially those with both negative permittivity
and negative permeability [known as left-handed metamaterials (LHMs)]. Here, by
going beyond the traditional concept of the combination of artificial
electronic and magnetic meta-atoms to design NIMs, we propose a novel LHM
composed of an array of simple upright split-ring pairs working in the near
infrared region. Our electromagnetic simulations reveal the underlying
mechanism that the coupling of the two rings can stimulate simultaneously both
the electric and magnetic resonances. The proposed structure has a highest
refractive index of -2, a highest figure of merit of 21, good air-matched
impedance and 180 nm double negative bandwidth, which excel the performances of
many previous proposals. We also numerically demonstrate the negative
refraction of this metamaterial in both the single-layer form and wedge-shaped
lens.
