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Speeding up computer processing the flashy way

25 Mar 2014

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Physicists from Ohio State University have demonstrated that information can flow through a diamond wire. In their experiment, electrons did not flow through diamond as they do in traditional electronics. Instead, they stayed in place and passed along a magnetic effect called "spin" to each other down the wire like a row of sports spectators doing "the wave."

Spin could one day be used to transmit data in computer circuits, and this new experiment, done at the Ohio State University, revealed that diamond transmits spin better than most metals in which researchers have previously observed the effect.

Researchers worldwide are working to develop so-called "spintronics" that could make computers simultaneously faster and more powerful.

Diamond has a lot going for it when it comes to spintronics, said lead investigator Chris Hammel, Ohio Eminent Scholar in Experimental Physics at Ohio State. It's hard, transparent, electrically insulating, impervious to environmental contamination, resistant to acids, and doesn't hold heat as semiconductors do.

"Basically, it's inert. You can't do anything to it. To a scientist, diamonds are kind of boring, unless you're getting engaged," Hammel said. "But it's interesting to think about how diamond would work in a computer."

The price tag for the diamond wire didn't reach engagement ring proportions, Hammel confirmed. It cost a mere $100, since it was made of synthetic, rather than natural, diamond.

The findings here represent the first very small step along a very long road that could one day lead to diamond transistors.

But beyond that, this discovery could change the way researchers study spin, Hammel said.

Electrons attain different spin states according to the direction in which they're spinning, up or down. Hammel's team placed a tiny diamond wire in a magnetic resonance force microscope and detected that the spin states inside the wire varied according to a pattern.

"If this wire were part of a computer, it would transfer information. There's no question that you'd be able to tell at the far end of the wire what the spin state of the original particle was at the beginning," he said.

Normally, diamond couldn't carry spin at all, because its carbon atoms are locked together, with each electron firmly attached to a neighbouring electron. The researchers had to seed the wire with nitrogen atoms in order for there to be unpaired electrons that could spin. The wire contained just one nitrogen atom for every three million diamond atoms, but that was enough to enable the wire to carry spin.

The experiment worked because the Ohio State physicists were able to observe electron spin on a smaller scale than ever before. They focused the magnetic field in their microscope on individual portions of the wire, and found that they could detect when spin passed through those portions.

The wire measured only 4um long and 200nm wide. In order to see inside it, they set the magnetic coil in the microscope to switch on and off over tiny fractions of a second, generating pulses that created 15nm wide snapshots of electron behaviour. They knew that spin was flowing through the diamond when a magnet on a delicate cantilever moved minute amounts as it was alternatively attracted or repelled by the atoms in the wire, depending on their spin states.

Even more surprising was that the spin states lasted twice as long near the end of the wire than in the middle. Based on ordinary experiments, the physicists would expect spin states to last for the same length of time, regardless of where the measurement was made. In this case, spin states inside the wire lasted for about 15ms, and near the end they lasted for 30ms.

Hammel's team suspects that they were able to witness this new effect in part because of how closely they were able to zoom in on the wire. As they focused their tiny window of observation on the tip of the wire, they witnessed spin flowing in the only direction it could flow: into the wire. When they panned along the wire to observe the middle, the "window" emptied of spin twice as fast, because the spin states could flow in both directions, into and out of the wire.

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