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Negative-index materials made easy
17 October 2003

Physicists have observed negative refraction in an ordinary crystal for the first time. The material, made by researchers at the National Renewable Energy Laboratory in the US, could now be used to make lenses that do not reflect light and to study novel optical phenomena (Y Zhang et al. 2003 Phys. Rev. Lett. 91 157404).

First proposed over thirty years ago, negative refractive index - or 'left-handed' - materials bend light in the opposite direction to ordinary materials. However, they were not demonstrated experimentally until 2000. Although some physicists argued at the time that only the phase velocity of the light was negatively refracted, rather than the group velocity, recent experiments and computer simulations have overcome this and other objections. Nevertheless, researchers have only ever observed negative refraction in complicated 'meta-materials' so far.

Now, Yong Zhang and co-workers have demonstrated total negative refraction in a 'twinned' alloy that contains yttrium, vanadium and oxygen. This commonly found ferroelastic material contains two uniaxial crystals whose optical axes are oriented symmetrically with respect to the interface. The researchers found that the interface could refract light of any frequency and electron waves as well. This is an improvement on previous negative-index materials that only worked for microwave radiation. Furthermore, depending on the angle of incidence, the interface could also positively refract light.

"This is the first time that both total refraction, that is zero reflection, and amphoteric refraction - both positive and negative refraction - have been seen in the same material," Zhang told PhysicsWeb. "Reflection is sometimes thought of as the penalty electromagnetic waves must pay when they are refracted. Our result shows that this does not have to be the case."

By demonstrating negative refraction in such a simple material, the researchers believe that it should now be easier to study new optical phenomena - such as the reversal of the Doppler effect and Cerenkov radiation. They say that their crystal could also be used to steer electron beams in nanoelectronic devices, and to transport high-power laser beams in reflection-free lenses.

Belle Dumé is Science Writer at PhysicsWeb

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Phys. Rev. Lett. 91 157404
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Belle Dumé

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