All known natural materials have a positive refractive index so that light that crosses from one medium to another gets slightly bent in the direction of propagation. In some artificial 'metamaterial' structures, however, negative refraction occurs such that light gets bent backwards as it enters the structure (Fig. 1). Thin films of high-temperature superconducting materials may achieve a similar effect according to new findings from researchers from the RIKEN Advanced Science Institute in Wako, and colleagues at the Ukrainian and Russian Academies of Sciences and Harvard University ("Layered superconductors as negative-refractive-index metamaterials" and "Surface Josephson Plasma Waves in Layered Superconductors above the Plasma Frequency: Evidence for a Negative Index of Refraction").
The realization of metamaterials and their unusual optical properties has enabled a number of novel devices, including 'invisibility cloaks' that can completely conceal an object, as well as perfect lenses that can generate images of an object with arbitrary precision. However, there is a drawback with metamaterials explains Franco Nori from RIKEN and the University of Michigan, USA, who led the research team. "Typically, these metamaterials consist of complex metallic wires and other structures that require sophisticated fabrication technology and are difficult to assemble."
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