Disruptions in a material’s atomic structure could act as “nano-pipelines” for efficient transport of charge and spin

Lines of shifted atoms, or dislocations, in electronic materials have long been considered detrimental due to their tendency to impede the flow of electricity.

But a new $7.5 million project led by the University of Michigan will instead embrace these imperfections in next-generation electronic devices, possibly enabling faster and more efficient information processing.

Funded by the Department of Defense, the project aims to understand how dislocations could be used as nano-pipelines to channel electrons while manipulating their spins. The project also involves researchers from the University of Illinois Urbana-Champaign.

While electronic devices that couple charge and spin, known as “spintronics,” are already used for information storage, they have not yet been fully developed for classical or quantum computation. Spin is an intrinsic property of the electron that can be thought of as its rotation. Electrons are said to have spin up or down directions, which could represent the 0s and 1s in computing.

“These nano-pipelines could revolutionize information technology like the silicon transistor did,” said Rachel Goldman, associate professor of materials science and engineering and director of applied physics, who is leading the project.

“Much in the way that you control the charge in a silicon transistor in two dimensions, here we’re going to control the charge and the spin, but we’re going to do it all in one dimension.”

Arrays of nano-pipelines would allow electrical signals to be conveyed in 3D space, breaking a bottleneck of current computing technology.

Today’s computers rely on electron charge for information processing, requiring a continuous supply of energy to avoid data loss during computations. Instead, spintronic devices do not have that requirement and may improve computing reliability. While spintronic devices have been proposed over the past two decades, they have been based upon semiconductors, in which the ability to maintain spin orientation is limited.

Topological insulators, alternatively, are an emerging class of materials that feature insulating interiors and highly conductive surfaces that enable the control of spin. However, electrons on the surfaces of topological insulators may lose their spin states as they change direction.

“What we want to do is take these topological materials and flip them outside-in,” said Cagliyan Kurdak, professor of physics in the College of Literature, Science, and the Arts. “We take their desirable surface properties and confine them to nano-pipelines to transport electrons and manipulate their spin.”

These nano-pipelines are so narrow that the electrons are unable to change direction and lose their spin states.

“Once you figure out this transport within a single dislocation, you could theoretically engineer an array of dislocations within the material,” said Kai Sun, professor of physics in the College of Literature, Science and the Arts. “You could then begin to convey electrical signals in 3D space, breaking a bottleneck of current computing technology.”

In this five-year project, the team will place their initial focus on developing theoretical and computational models for a specific suite of topological materials and start fabricating them with dislocations using the state-of-the-art facilities at U-M and UIUC, including U-M’s Lurie Nanofabrication Facility and Michigan Center for Materials Characterization, as well as UIUC’s Materials Research Laboratory and Holonyak Micro and Nanotechnology Lab.

Once the team has demonstrated charge transport along dislocations, they will examine the new quantum states hosted by the dislocations, including Majorana modes, a long-sought quasi-particle that is crucial for topological quantum computing.

“It’s clearly a highly challenging task which will require multidisciplinary expertise and a proven ability to work together,” said Ctirad Uher, the C. Wilbur Peters Collegiate Professor of Physics at U-M.

Made up of experts in topological physics, materials synthesis, transport measurements and more, the group’s history of collaboration spans two decades, through shared undergraduate and graduate students, federal grants, archival publications and an Energy Frontiers Research Center.

“When I was a Ph.D. student, I used to make sketches in my lab notebook about how I wanted to study the effect of dislocations on electron transport. I’ve always been looking for a way to come back to that problem and here it is,” Goldman said. “From a career standpoint, I’d say that this is probably the most exciting project I’ve ever had the opportunity to work on.”

The award is one of 31 funded by the DoD’s Multidisciplinary University Research Initiative program, which funds teams of investigators to tackle high priority opportunities that intersect multiple disciplines.