Materials that bend light in unnatural ways are often touted as the path to futuristic technologies such as cloaking devices and super-powered lenses. But such materials are hard to make, but scientists have now discovered a simpler way using electrons.
At Harvard University’s School of Engineering and Applied Sciences, a team of researchers led by Hosang Yoon and Donhee Ham showed that using ordinary semiconductors and confining electrons to a two-dimensional plane they could make a material with a so-called negative refractive index that bends radio waves the “wrong” way, and does so a hundred times better than other methods.
A refractive index is a measure of how much a material bends light. An index of 1 means no bending at all. Diamonds have that nice prism effect because they have an index of about 2.42, whereas air bends light hardly at all. Light – and that includes radio waves – bends because as it travels through anything other than a vacuum it slows down. Most materials always have a positive refractive index. That means that if light is approaching a denser, higher-index material from a lower-index one it gets bent to the right if the denser stuff is on that same side.
This all changes if the material has a negative index – as metamaterials do. In that case, the bend would be to the left. An object surrounded by a metamaterial would scatter the light away from it, making it invisible.
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