Negative refraction for electrons passing a boundary has been observed by a team including Avik Ghosh, an Affiliated Professor of Physics.  The results have been published in Science.

For more, see the SEAS Press Release:
http://enews.seas.virginia.edu/electrons-in-graphene-behave-like-light-only-better/

For the Science article, see:
http://science.sciencemag.org/content/353/6307/1522