Negative and positive refraction

At the same crystal interface has been demonstrated. In negative refraction, which takes place in “left-handed materials” (LHMs), a light ray impinging on an interface never crosses the normal to that interface. Until now all LHMs have been so-called metamaterials composed of rods and split-ring resonators mounted on boards (see Physics Today, May 2000, page 17 , and the second Correction in July 2000, page 77 ). Now, physicists at the National Renewable Energy Laboratory in Golden, Colorado, have found a class of LHMs made from bicrystals that display a certain “domain twin” structure. Such a structure occurs in both natural and easily engineered ferroelastic materials and is shown here in an electron micrograph of a III–V semiconductor alloy with copper–platinum ordering. The researchers used a single YVO₄ bicrystal to demonstrate, depending on the angle of incidence, both positive and negative refraction. What’s more, the schizophrenic—called amphoteric—refraction occurred for ballistic electrons as well as for light and suffered no losses to reflection at the interface. (Y. Zhang, B. Fluegel, A. Mascarenhas, Phys. Rev. Lett. 91 , 157404, 2003 http://dx.doi.org/10.1103/PhysRevLett.91.157404 .)