astro
11-18-2005, 09:15 AM
Graphite Found to Exhibit Surprising Quantum Effects (http://www.sciam.com/article.cfm?chanID=sa003&articleID=00033D41-7354-1372-B35483414B7F0000)
Pencil lead is actually graphite--a carbon mineral that, when dragged across paper, leaves writing behind because its atomic layers separate easily. This also means that it is an excellent conductor of electricity. Last year, Andre Geim of the University of Manchester in the U.K. used adhesive tape to strip graphite down to a layer just one atom thick; they called this superthin layer of graphite "graphene."
Experiments on graphene have revealed some strange phenomena, as detailed in two papers in today's Nature. The two-dimensional material remains capable of conducting electricity thanks to the free-floating electron in the honeycomb structure of carbon atoms. But these electrons display some unusual properties.
Geim's team found that they do not slow down, even at very low temperatures. In essence, the electrons act as if they have no mass, or no "rest mass," to use the more precise phrase from special relativity. It also means that graphite--at least the two-dimensional variety--never stops conducting. Dubbing these pseudo-relativistic particles "massless Dirac fermions," the researchers also proved that they travel far faster than electrons in other semiconductors. As such, they conform to that famous equation E=mc2 (with their actual speed, some 400 times slower than the speed of light, standing in for c).
Pencil lead is actually graphite--a carbon mineral that, when dragged across paper, leaves writing behind because its atomic layers separate easily. This also means that it is an excellent conductor of electricity. Last year, Andre Geim of the University of Manchester in the U.K. used adhesive tape to strip graphite down to a layer just one atom thick; they called this superthin layer of graphite "graphene."
Experiments on graphene have revealed some strange phenomena, as detailed in two papers in today's Nature. The two-dimensional material remains capable of conducting electricity thanks to the free-floating electron in the honeycomb structure of carbon atoms. But these electrons display some unusual properties.
Geim's team found that they do not slow down, even at very low temperatures. In essence, the electrons act as if they have no mass, or no "rest mass," to use the more precise phrase from special relativity. It also means that graphite--at least the two-dimensional variety--never stops conducting. Dubbing these pseudo-relativistic particles "massless Dirac fermions," the researchers also proved that they travel far faster than electrons in other semiconductors. As such, they conform to that famous equation E=mc2 (with their actual speed, some 400 times slower than the speed of light, standing in for c).