MIT physicists and colleagues have created a five-lane superhighway for electrons that could allow ultra-efficient electronics and more. The work, reported in the May 9 issue of Science, is one of several important discoveries by the same team over the last year involving a material that is essentially a unique form of pencil lead.
"This discovery has direct implications for low-power electronic devices because no energy is lost during the propagation of electrons, which is not the case in regular materials where the electrons are scattered," says Long Ju, an assistant professor in the MIT Department of Physics and corresponding author of the paper.
The phenomenon is akin to cars traveling down an toll road as opposed to those traveling on a suburban road The suburban cars can be stopped or slowed by other drivers making abrupt stops or U-turns that disrupt an otherwise smooth journey
A new material
The material behind this work, known as rhombohedral penta layer graphene, was discovered two years ago by physicists led by Ju. "We found a goldmine, and every scoop is revealing something new," says Ju, who is also affiliated with MIT's Materials Research Laboratory.
In a Nature Nanotechnology paper last October Ju and colleagues reported the discovery of three important properties arising from rhombohedral graphene. For example, they showed that it could be topological, or allow the unimpeded movement of electrons around the edge of the material but not through the middle. That resulted in a superhighway but required the application of a large magnetic field some tens thousands of times stronger than the Earth's magnetic field.
In the current work, the team reports creating the superhighway without any magnetic field.
Tonghang Han, an MIT graduate student in physics, is a co-first author of the paper. "We are not the first to discover this general phenomenon, but we did so in a very different system. And compared to previous systems, ours is simpler and supports more electron channels," explains Ju. "Other materials can only support one lane of traffic on the edge of the material. We suddenly bumped it up to five."
How it works
Pencil lead, or graphite, is composed of graphene, a single layer of carbon atoms arranged in hexagons resembling a honeycomb structure. Rhombohedral graphene is composed of five layers of graphene stacked in a specific overlapping order.
Ju and colleagues isolated rhombohedral graphene thanks to a novel microscope Ju built at MIT in 2021 that can quickly and relatively inexpensively determine a variety of important characteristics of a material at the nanoscale. Pentalayer rhombohedral stacked graphene is only a few billionths of a metre thick.
In the current work, the team tinkered with the original system, adding a layer of tungsten disulfide (WS2). "The interaction between the WS2 and the Penta layer rhombohedral graphene resulted in this five-lane superhighway that operates at zero magnetic field," says Ju.
Reference Elizabeth A. Thomson, Materials Research Laboratory, Massachusetts Institute of Technology
