Quantum insulators may improve speed of digital information transfer

By stacking layers of QAH insulators, researchers were able to create a multilane highways for fast-flowing electrons. Photo by Zhao et al./Nature
By stacking layers of QAH insulators, researchers were able to create a multilane highways for fast-flowing electrons. Photo by Zhao et al./Nature

Dec. 16 (UPI) -- The phenomenon known as the quantum anomalous Hall effect describes the ability of electrons to move freely along at the outer edges of materials. Electrons propelled by the QAH effect can travel at high speeds without losing energy.

For the first time, researchers have generated the QAH effect in a multilayered insulator, creating a kind of multilane highway, across which electrons can travel.


The breakthrough, described Wednesday in the journal Nature, could be used to build more energy efficient electronic devices.

"Increasing the number of electrons in most metals results in a sort of traffic jam because electrons moving in different directions get scattered and repel each other," lead researcher Cui-Zu Chang said in a news release.

"But in QAH insulators, electron flow is constrained to the edges, and electrons on one edge can only go in one direction and those on the other edge can only go the opposite direction, like splitting a road into a two-lane highway," said Chang, an assistant professor of physics at Penn State University.


By layering QAH insulators, Chang and his researcher partners created parallel highways, which allowed electrons to move in different directions.

QAH insulators are created by magnetizing topological insulators, thin layers of insulating material, measuring just a few atoms thick.

Researchers were able to precisely control which parts of the insulator becomes magnetized using a technique called diluted magnetic doping.

The technique involves the targeted introduction of magnetic impurities during the insulator fabrication process.

"QAH insulators are of particular interest because they theoretically have no energy dissipation, meaning that electrons do not lose energy in the form of heat as electrical current flows along the edges," said study co-author Chao-Xing Liu.

"This unique property makes QAH insulators a good candidate for use in quantum computers and other small, fast electronic devices," said Liu, an associate professor of physics at Penn State.

Until now, researchers had only been able to create a single two-lane electron highway using QAH insulators. The new multilayer insulated features a five-lane superhighway. Because electrons can flow along both sides of each insulator layer, the insulators feature 10 total electron flows.

"We do see some dissipation of current at connection points between QAH insulators and metallic electrodes, which occurs in the form of heat," Liu said.


"You can think of it like the on and off ramps of a busy highway, where the narrow merge lane into local traffic slows you down. By building more parallel highways, more merge lanes can connect the highways to local traffic, so that the overall speed of the whole traffic system can be greatly improved," Liu said.

The number of lanes hosted by a QAH insulator is known as its Chern number.

Researchers found they could manipulate the Chern number by changing the thickness of the QAH layers or by altering the concentration of magnetic impurities during the magnetic doping process.

For now, the new technology only works at very low temperatures, but researchers are confident that material solutions will allow them to replicate their multilayered QAH insulator at higher temperatures and integrate the technology into electronic devices.

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