Inside a pencil's tip is a metal that's a veritable playground for physicists

Sure, it looks like an ordinary writing implement. But slice the graphite tip of your pencil down to a one-atom-thick plane, and behold the strangest predictions of quantum relativity and string theory.

According to a paper published in the November 10th issue of Nature, researchers at the University of Manchester have observed the effects of relativity in not the bending of light from distant stars, but small sheets of carbon called graphene, a two-dimensional crystal created by stripping away a super-thin layer of graphite.

Andre Geim, a lead author of the paper, said the electrons in graphene don’t act like individual particles. In fact, the whole sheet of electrons behaves as if it were one large pseudo-particle spread out over the entire lattice.

“In our experiments we have this unique situation that string theorists used in their models: We have a massless [pseudo-particle] who is charged,” said Kostya Novoselov, who co-led the study with Geim.

Massless but charged particles appear in all modern unification theories. After theorizing, researchers face the challenge of introducing mass into their models—the charged particles we encounter on a daily basis all have mass. The traits of graphene fit the unification models. But this is “cute physics,” as Novoselov said, not a proof of string theory.

Graphene’s qualities also allowed the experimenters to easily manipulate the state of the pseudo-particle with an electric or magnetic field.

The Manchester team used graphene to demonstrate the effects of Einstein’s theory of relativity. By bringing the pseudo-particle to a desired energy level and observing its behavior in a magnetic field, they showed that the pseudo-particle gains an effective mass proportional to its energy, in accordance with Einstein’s equation E=mc2.

Geim said graphene has one extremely useful electronic characteristic: Its electrons behave as one large pseudo-particle, so graphene has less resistance than most metals and conducts electricity even as its concentration tends to zero.

“It’s like bullets. Electrons shoot from one side to another side of our material without scattering,” said Geim. “This is the holy grail of all microelectronics: to make a transistor, a so-called ‘ballistic transistor,’ where electrons move without any scattering.”

A ballistic transistor made from graphene would be wildly useful for its ability to send strong signals extremely quickly—as well as its stability under ambient conditions.

Geim said the two-dimensional crystal is a new class of material, whose properties have yet to be fully explored and exploited.

“A comparison could be [made to] polymers,” he said. “When they were first discovered more than a century ago, it was just another class of materials. But then it turned out to be quite useful.”

According to Novoselov, it is too early to determine exactly what applications the ballistic transistor will have, but it could improve the performance of mobile phones and satellites.

After proving relativity, giving an ego boost to the string theorists, and entering the ballistic transistor arena, the two-dimensional crystal has already proved fairly useful—at least in theory.

Originally published November 11, 2005

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