This year’s Nobel Prize in Physics has been awarded to three physicists, “for theoretical discoveries of topological phase transitions and topological phases of matter.” Two of the scientists uncovered why the spins of atoms inside particular kinds of magnets form messy patterns at low temperatures. This theoretical work, performed in the 1970s, is still leading engineers to develop better and more efficient superconductors.
Every atom in a magnet acts like a mini bar magnet: its spin—a quantum mechanical property—points in a certain direction. If every spin in a lump of material points in the same direction, it’s like you have one big bar magnet.
Michael Kosterlitz, now at Brown University, and David J. Thouless, now at the University of Washington, modeled 2-D layers of ferromagnets—the kind of magnets that stick to the fridge—at low temperature. Their thought experiments indicated that the atomic spins were not fully aligning over a long distance. In other words, the spins did not come together to form one big bar magnet.
They used the concept of vortices—pockets of atoms inside magnets whose spins are oriented in a way that makes the pocket resemble the eye of a hurricane—to explain the effect. These vortices change the spins of nearby atoms.
The Nobel Prize winners “were really the first to use vortices to explain something that’s very profound in condensed matter physics,” says Michael Lawler, a theoretical physicist at Binghamton University in New York who studies magnetism and superconductivity.
At a press conference Tuesday, Kosterlitz said of his Nobel work: “There aren’t real practical applications and it’s not going to lead to any fancy new devices” because most devices are not two-dimensional.
Yet Lawler says that after the discovery, physicists started looking at other special materials where organization becomes disrupted. In particular, they looked at superconductors—materials that don’t resist the flow of electricity and allow large currents to pass on a relatively small wire.
Promising high-temperature superconductors are made of layers of 2-D material, he says. Inside superconductors, vortices take the form of whirlpools of electrons and have a disorder-inducing effect.
Understanding the vortices mechanism is useful, Lawler says, in part because it helps researchers figure out how they introduce resistance in a superconductor.
Removing the vortices allows engineers to optimize superconductors’ performance, he says, so cables could someday deliver more power to more people. As an example, research in 2008 revealed that tightly coupling the layers of high-temperature superconducting material generates 3-D vortices, which don’t move around as much as 2-D vortices. The result: They don’t introduce as much resistance.
Besides Kosterlitz and Thouless, who also studied conductance with electrically conducting layers, Duncan Haldane was recognized for his studies of small chains of magnets. The prize was awarded to the researchers for their use of topology: mathematics that describes global relationships that stay the same when local relationships between elements change.