Because of it's highly ionized state, the state of
matter called
plasma has a
negative index of refraction. In 1968, the Russian physicist Victor Veselago found that in order for a
material to have a negative index of refraction, it must behave as a perfect
plasma. The index of refraction in
plasma is affected by the
plasma density and
magnetic field. The field causes
faraday rotation, which is a change in orientation of the right and left hand
polarized vectors of an
electromagnetic wave.
Sheldon Schultz, David Smith, and Richard Shelby at the University of California at San Diego constructed a device consisting of copper rings connected by wires that displayed a negative index of refraction in 2000.