Gilbert, Mason's research allows better understanding of topological insulators

New research at Illinois puts researchers one step closer to understanding novel materials called “topological insulators,” and how these differ from traditional semiconducting materials.

Associate Professor Matthew Gilbert, along with collaborator Nadya Mason, an associate professor in Illinois’ Department of Physics, conducted the work, which was published in Nature Communications last month. Gilbert is also affiliated with the Micro and Nanotechnology Laboratory, and Mason is affiliated with the Frederick Seitz Materials Research Laboratory.

Topological insulators are materials having insulating interiors but surfaces that allow for the flow of electrons. They have far different physical qualities than standard semiconducting materials, like silicon, Gilbert said.

“While their properties are interesting from a fundamental point of view, little has been done to determine the role of these materials in designing new information-processing devices and architectures,” he said.

This research focuses on conductance oscillations in nanowires made of the topological insulator Bi₂Se₃, demonstrating that conduction occurs only on the surface. Such surface conduction may eliminate the resistivity and related power dissipation due to bulk scattering that occurs in typical device materials such as copper and silicon.

In addition, the research found conductance behavior consistent with a “topological mode” that can be turned on and off with a magnetic field. This unique topological mode is a necessary component of proposed fault-tolerant quantum computing using these materials, yet has not previously been demonstrated in nanowires.

Gilbert and Mason worked with postdoc Sungjae Cho, now with the Korea Advanced Institute of Science and Technology, alumnus Brian Dellabetta (MS ’11, PhD ’14), and materials grower Genda Gu and his group at Brookhaven National Laboratory.

This work allows Gilbert and Mason a better understanding of how the properties of topological insulator will change device functions and information-processing technologies, from switching to interconnects and inductors, to quantum computers.

“This is an important step in understanding how to control and exploit the unique properties of the highly conductive surfaces by understanding how electrons move on the surface when electric and magnetic fields are present. For example, we can potentially realize a new, more efficient form of interconnect using these materials,” Gilbert said.

Gilbert expects the materials could prompt the design of totally new systems that take advantage of the insulators’ unique properties.

“In a sense, that’s what is nice about them; you can be creative and try a lot of ideas,” Gilbert said. “There’s no path to follow.”

In the next phase of the research on topological insulators, researchers will examine how these properties change when combined with different materials.

“In particular, it is important to consider how the properties of the surface conduction change in the presence of superconducting and magnetic materials,” Gilbert said. “The different types of physical excitations produced by topological insulators when combined with such materials are predicted to form the base of a new type of quantum computing that is immune from disorder. Understanding how the dissimilar materials interact to form these states is of utmost importance.”