In 1887, while discovering RF waves in his Karlsruhe Polytechnikum laboratory, Heinrich Hertz already knew that light could also be described as an electromagnetic wave. As such, one could say it “walks on two legs”: For a single plane wave, light has an electric leg, a perpendicular magnetic leg, and a walking direction normal to both of them. Thus, obtaining complete control over light in materials or structures requires the ability to independently manipulate both legs. During the centuries that scientists have been striving to do that, however, natural substances have allowed only the electric-field component of a light wave to be directly controlled. The interaction of atoms with the magnetic-field component of light is normally just too weak.

With artificial materials known as metamaterials, that limitation was overcome a decade ago, an achievement that enabled independent control of the electric- and magnetic-field components, at least up to microwave...

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