Lead Author

Since the early 1990s, physicist Steven Louie at the University of California, Berkeley, has been probing the useful properties of carbon-based nanomaterials. On page 347, Louie and his co-workers present a theoretical prediction of some potentially intriguing properties of nanoscale ribbons of graphene. The team suggests that the non-metallic graphene could be induced to take on some characteristics of a metal, such as magnetism. The result would be a 'half-metal' that could potentially be used in spintronics — a refined version of electronics that makes use of not only the electrons' charge but also their 'spin'. The calculations might pave the way for fresh approaches to spintronic devices using graphene nanoribbons. Louie spoke to Nature about his work.

How can a non-metallic element such as carbon have metal properties?

A graphene ribbon has a unique geometry in that it has zigzag edges. Low-energy electrons, with their spins aligned either up or down, are able to run freely along these edges. It is the edge electrons that give rise to magnetism. As the magnetic states are spatially separated across the ribbon, you can use a transverse electric field to shift their energy, thereby creating charge carriers with the same spin, making the system a half-metal. Another electric field along the ribbon length can then be used to drive a spin current.

What is holding back exploration of these properties in organic materials?

First, half-metals are very rare, and organic materials tend not to be magnetic. Typically, electrons in organic materials form covalent bonds — the spin up and spin down are paired in the bond so there is no net spin — or the spins are randomly oriented. But in a zigzag graphene nanoribbon, the atoms on the edge behave differently, forming edge states capable of having a net spin. You wouldn't find this behaviour in a perfect buckyball or a nice, long carbon nanotube.

Why would organic materials be advantageous in electronics?

The driving force for wanting organic materials is that they are composed of abundant and non-toxic elements. It would be great to have cheap, high-performance electronics that are less harmful to the environment.

Will spintronics replace electronics?

I don't know whether spintronics will eventually replace electronics, but it will enhance today's electronics. The challenge now is to create the right material to efficiently generate spin current.