A sheet of graphene, a carbon lattice just one atom thick, under a powerful laser beam behaves like a road where a toll barrier suddenly appears. Electrons that were freely racing through the material suddenly hit a forbidden zone: an energy gap they cannot leap across. This was predicted theoretically before, but no one had ever seen it directly.
An international team of physicists fired short, intense light pulses at graphene. The light forced the electrons to move in sync, like a crowd marching in step on a bridge. Where energy levels used to cross, a gap emerged — spectroscopy with time and angle resolution showed it directly. The gap turned out to be anisotropic: wider in some directions, narrower in others, and vanishing entirely at two special points. These points, the so-called Dirac nodes, are protected by symmetry, like the two poles on a globe that cannot be removed without tearing the map.
This is the first direct experiment confirming that light can reshape the electronic structure of graphene. Looking ahead, such "light-dressed" materials could become the basis for transistors switched by lasers or for quantum devices whose properties change on the fly. Graphene, once made with tape and pencil, again proves to be a testing ground for ideas that only yesterday lived on paper.
Graphene is the thinnest material in the world: a stack of a million sheets would be as thick as a human hair.
In Neal Stephenson's novel The Diamond Age, matter is programmed with light — the graphene experiment takes the first step toward such technology.