Technique readies graphene for quantum computing

Under an extremely powerful magnetic field and at extremely low temperatures, the team found that graphene can effectively filter electrons according to the direction of their spin, something that cannot be done by conventional electronic systems. Under typical conditions, sheets of graphene behave as normal conductors - with current flowing throughout the two dimensional flake. If you turn on a magnetic field perpendicular to the graphene flake, however, the behavior changes: Current flows only along the edge, while the bulk remains insulating. Moreover, this current flows only in one direction - clockwise or counterclockwise, depending on the orientation of the magnetic field - in a phenomenon known as the quantum Hall effect. In the new work, the MIT researchers found that if they applied a second powerful magnetic field - this time in the same plane as the graphene flake - the material's behavior changes yet again: Electrons can move around the conducting edge in either direction, with electrons that have one kind of spin moving clockwise while those with the opposite spin move counterclockwise. "We created an unusual kind of conductor along the edge, virtually a one dimensional wire," said researcher Andrea Young. "The segregation of electrons according to spin is a normal feature of topological insulators, but graphene is not normally a topological insulator. We're getting the same effect in a very different material system." What's more, by varying the magnetic field, the researchers found they could turn these edge states on and off. "This switching capability means that, in principle, we can make circuits and transistors out of these, which has not been realised before in conventional topological insulators," Young added. The researchers claim the discovery represents a 'new direction' in topological insulators, and believe it could ultimately lead to a novel way of making a kind of quantum computer, something that researchers worldwide have tried to do, without success, for decades. "We don't really know what it might lead to, but it opens our thinking about the kind of electrical devices we can make," Young concluded.