Our starting points in understanding what all the fuss is about are the atomic and electronic properties of graphene. Carbon atoms in the monoatomic layer are arranged in a perfect honeycomb pattern. Each atom binds symmetrically to three neighbors through strong bonds. This 2D structure has the exceptional stability also found in its 3D cousins—soot, the carbon buckyballs, and nanotubes. In graphene, the hexagonal bonding means that every carbon atom contributes a free electron, and this gives graphene excellent conductivity.

Graphene does not exist in the natural state because it curls into soot, nanotubes, or buckyballs. Only in 2004 did physicists finally tame its springy behavior. In Hot Paper #4, Andre Geim and colleagues (University of Manchester, U.K., and the Institute for Microelectronics Technology, Chernogolovka, Russia) showcase the exciting electronic properties of graphene. First they had to fabricate graphene films, which they achieved with remarkable ease by repeated peeling off one layer at a time from mesas of multilayer graphene flakes deposited on oxidized Si wafers until as little as a single-layer flake remained. They then tested more than 60 electronic devices made from these thin films. The electronic properties of the 1-, 2-, and 3-atomic-layer films showed that their mobile electrons behaved differently to electrons in 2D semiconductor devices. That’s why #4 is attracting attention.

The graphene films described in #4 are metallic and of high quality. Modern electronics relies on using electric fields to control the flow of electric current through the device. The ability of physicists to improve Si devices must be close to the limit, hence the search for alternative materials with properties that can be controlled by electric fields. Attempts to develop all-metallic transistors have failed because metal films with thicknesses of a few nm are thermodynamically unstable. Geim’s group reports the observation of an electric field effect in stable graphene films, the first such discovery in a metallic material.

The breakthrough reported in #4 suggests that graphene may be the best material for metallic transistors. At any rate, at this time it is the only such material. Metallic transistors offer scalability downwards, so devices could be made smaller, they would consume less energy, and they would be much faster than Si.

In a semiconductor there is a quadratic relationship between the energy and momentum of the electrons. But in graphene that relationship is linear. Papers #2 (Geim’s group) and #3 (Philip Kim’s group, Columbia University, New York), published side by side in Nature, report on an important consequence of the linear relationship. They independently discovered that electrons move through the films as if they have no mass. That’s because the energy-momentum relationship means that electron transport is governed by the relativistic Dirac equation.

Both teams report on a variety of intriguing electronic properties. In effect the electrons in graphene are a 2D gas of Dirac fermions, hence the title of #2. Quantum effects come into play: there’s a new half-integer quantum Hall effect for both electrons and holes.