Experimental demonstrations of metamaterials with negative index of refraction have been limited to microwave and IR frequencies. In this work, a freestanding multilayer thin-film metamaterial showing a strong negative index of refraction at terahertz frequencies is fabricated and characterized. The metamaterial consists of periodically arranged H-shaped wire-pair resonant structures separated by a 14.5-(mu)m-thick and enclosed between two 26-(mu)m-thick layers of benzocyclobutene polymer. Complex reflection and transmission parameters of the metamaterial are measured via terahertz time-domain spectroscopy and are used for the extraction of refractive material properties. Our results show good agreement with finite element field simulations.
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