Physicists at MIT have created a five-lane quantum superhighway for electrons

HAVE physicists developed a new form grapheneit creates a five-lane electron superhighway that allows ultra-efficient electron movement without energy loss.

This breakthrough in rhombohedral five-layer graphene could transform low-power electronic devices and works through the quantum anomalous Hall effect at zero magnetic field.

MIT physicists and collaborators have created a five-lane superhighway for electrons that could enable ultra-efficient electronics and more.

The work, recently published in the journal Scienceis one of several important discoveries by the same team over the past year involving a material that is a unique form of graphene.

“This discovery has direct implications for low-power electronic devices because there is no energy loss when electrons propagate, which is not the case in common materials where electrons are scattered,” says Long Ju, an assistant professor in the Department of Physics. and corresponding author Science paper.

This phenomenon is similar to cars driving on the open highway as opposed to those moving through neighborhoods. Cars in the neighborhood can be stopped or slowed by other drivers who stop or swerve in the opposite direction, disrupting an otherwise smooth commute.

A new material: rhombic graphene

The material behind this work, known as rhombohedral five-layer graphene, was discovered two years ago by physicists led by Ju. “We’ve found a gold mine, and every scoop reveals something new,” says Ju, who is also affiliated with MIT’s Materials Research Laboratory.

IN Nature Nanotechnology last October, Ju and his colleagues announced the discovery of three important properties arising from rhombohedral graphene. For example, they showed that it could be topological, or allow electrons to move freely around the edge of the material but not through the center. The result was a superhighway, but it required the use of a large magnetic field that was several tens of thousands of times stronger than Earth’s magnetic field.

Enhancement of graphene electron channels

In the current work, the team reports the creation of a superhighway without a magnetic field.

Tonghang Han, a graduate student in physics at MIT, is co-first author on the paper. “We are not the first to discover this general phenomenon, but we did it in a very different system. And compared to previous systems, ours is simpler and also supports more electron channels.” Ju explains, “other materials can only support one lane at the edge of the material. Suddenly we increased it to five.”

Other co-authors of the paper who contributed equally to the work are Zhengguang Lu and Yuxuan Yao. Lu is a postdoctoral fellow in the Materials Research Laboratory. Yao led the work as a visiting undergraduate student from Tsinghua University. Other authors are MIT physics professor Liang Fu; Jixiang Yang and Junseok Seo, both MIT physics graduates; Chiho Yoon and Fan Zhang of the University of Texas at Dallas; and Kenji Watanabe and Takashi Taniguchi of the National Institute for Materials Science in Japan.

How does it work

Graphite, the primary component of solids, consists of many layers of graphene, a single layer of carbon atoms arranged in hexagons resembling a honeycomb structure. Rhombohedral graphene consists of five layers of graphene stacked in a specific overlapping order.

Ju and colleagues isolated rhombohedral graphene thanks to a new microscope Ju built at MIT in 2021, which can quickly and relatively cheaply determine a number of important properties of the material at nanoscale. Five-layer rhombohedral layered graphene is only a few billionths of a meter thick.

In the current work, the team tinkered with the original system and added a layer of tungsten disulfide (WS₂). “Interaction between WS₂ and five-layer rhombohedral graphene resulted in this five-lane superhighway that works at zero magnetic field,” says Ju.

Comparison with superconductivity

The phenomenon Ju’s group discovered in rhombohedral graphene, which allows electrons to travel without resistance in a zero magnetic field, is known as the quantum anomalous Hall effect. Most people are more familiar with superconductivity, a completely different phenomenon that does the same thing but happens in very different materials.

Ju notes that although superconductors were discovered in 1910, it took about 100 years of research to coax the system to work at the higher temperatures necessary for applications. “And the world record is still well below room temperature,” he notes.

Similarly, the diamond-shaped graphene superhighway currently operates at about 2 kelvin, or -456 degrees Fahrenheit. “Raising the temperature will take a lot of effort, but as physicists it’s our job to provide insight; another way to realize it [phenomenon]” says Ju.

Implications and future prospects

The discoveries about rhombohedral graphene were the result of painstaking research that was not guaranteed to work. “We tried many recipes over many months,” says Han, “so it was very exciting when we cooled the system down to a very low temperature and [a five-lane superhighway operating at zero magnetic field] she just jumped out.”

Ju says, “It’s very exciting to be the first to discover a phenomenon in a new system, especially in the material we’ve uncovered.”

Reference: “Large quantum anomalous Hall effect in spin-orbit near rhombohedral graphene” by Tonghang Han, Zhengguang Lu, Yuxuan Yao, Jixiang Yang, Junseok Seo, Chiho Yoon, Kenji Watanabe, Takashi Taniguchi, Liang Fu, Fan Zhang and Long Ju, May 9, 2024, Science.
DOI: 10.1126/science.adk9749

This work was supported by a Sloan Fellowship; US National Science Foundation; US Office of the Assistant Secretary of Defense for Research and Engineering; Japan Society for the Promotion of Science KAKENHI; and the World Premier International Research Initiative of Japan.