Topological insulators could speed up switching between 1s and 0s
One of science’s newest wonder materials may find its way into computers.
A study published in the July 24 Nature reveals that electrons coursing through the materials known as topological insulators can manipulate magnetic components like the ones in computer memory. The research represents one of the first attempts to find real-world uses for topological insulators.
“This is the first proposal I have seen … which does not appear to be prima facie absurd,” says Sankar Das Sarma, a condensed matter theoretical physicist at the University of Maryland in College Park. “Purely scientifically, this proposal makes sense.”
Since predicting the existence of topological insulators in 2005, physicists have salivated over the materials’ unique properties (SN: 5/22/10, p. 22). For the most part topological insulators are, as the name suggests, insulators. But on their surfaces, electrons scurry along unimpeded and in strict formation: All electrons moving in a particular direction have the same spin.
Many scientists are digging into the fundamental physics of these materials, which include bismuth selenide and mercury telluride. But Penn State condensed matter physicist Nitin Samarth wanted to do something useful with them. He found inspiration in the work of Cornell University condensed matter physicist Dan Ralph, whose team is trying to revamp computer RAM and hard drives.
Most current hard drives store data as 1s and 0s in small chunks of magnetic wafers that resemble compass needles — if a chunk is magnetically oriented in one direction it’s a 1; in the other it’s a 0. Flipping a 1 to a 0 (or vice versa) requires generating magnetic fields, a relatively slow and inefficient process that limits devices’ speed and capacity (SN: 10/19/13, p. 28).
To accelerate the process, Ralph’s team wants to flip those compass needles with electrons’ spin. His team has built experimental devices in which electrons brush past those compass needles and, because of their spin, provide a subtle torque — like a spinning figure skater nudging a stationary skater into motion. The key to a successful device, Ralph says, is maximizing torque by generating currents of electrons with the same spin.
Matched spins are the bread and butter of topological insulators. So Ralph’s and Samarth’s groups teamed up to test whether electrons racing across the surface of a topological insulator could manipulate a magnetic material with their spins. They layered a magnetic material similar to ones used in computers, a nickel-iron wafer, atop the topological insulator bismuth selenide and sent an alternating current of electrons through the device. Each electron in the bismuth selenide exerted about 10 times as much torque as electrons in any other material that has been tested.
The new study shows that a topological insulator’s electrons can provide enough torque for a memory device, Samarth says. Now he and his colleagues are on to the next challenge: building a rudimentary one.
A.R. Mellnik et al. Spin-transfer torque generated by a topological insulator. Nature. Vol. 511, July 24, 2014, p. 449. doi: 10.1038/nature13534.