Topological Matters: Toward a New Kind of Transistor

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Michael Fuhrer, a physicist at Monash University who participated in the study, said, “This discovery is a step in the direction of topological transistors that could transform the world of computation.”

He added, “Ultra-low energy topological electronics are a potential answer to the increasing challenge of energy wasted in modern computing. Information and communications technology already consumes 8% of global electricity, and that’s doubling every decade.”

In the latest study, researchers grew the material samples, measuring several millimeters on a side, on a silicon wafer under ultrahigh vacuum at the ALS Beamline 10.0.1 using a process known as molecular beam epitaxy. The beamline allows researchers to grow samples and then conduct experiments under the same vacuum conditions in order to prevent contamination.

This beamline is specialized for an X-ray technique known as angle-resolved photoemission spectroscopy, or ARPES, which provide information about how electrons travel in materials. In typical topological materials, electrons flow around the edges of the material, while the rest of the material serves as an insulator that prevents this flow.

Some X-ray experiments on similar samples were also performed at the Australian Synchrotron to demonstrate the ultrathin Na3Bi was free-standing and did not chemically interact with the silicon wafer it was grown on. Researchers had also studied samples with a scanning tunneling microscope at Monash University that helped to confirm other measurements.

“In these edge paths, electrons can only travel in one direction,” said Mark Edmonds, a physicist at Monash University who led the study. “And this means there can be no ‘back-scattering,’ which is what causes electrical resistance in conventional electrical conductors.”

In this case, researchers found that the ultrathin material became fully conductive when subjected to the electric field, and could also be switched to become an insulator across the entire material when subjected to a slightly higher electric field.

Mo said that the electrically driven switching is an important step to realizing applications for materials—some other research efforts have pursued mechanisms like chemical doping or mechanical strain that are more challenging to control and to perform the switching operation.

The research team is pursuing other samples that can be switched on and off in a similar way to guide the development of a new generation of ultralow-energy electronics, Edmonds said.

The Advanced Light Source is a DOE Office of Science User Facility.

Scientists from the Australian Synchrotron, Singapore University of Technology and Design, National University of Singapore, University of Illinois at Urbana-Champaign, and YALE-NUS College in Singapore also participated in the study. The work was supported by the U.S. Department of Energy’s Office of Science, the Australian Research Council’s Centers of Excellence and DECRA Fellowship programs, the International Synchrotron Access Program, and the Monash Center for Atomically Thin Materials Research.

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