'Graphene superhighway' allows electronic devices to use much less power

Physicists have created a five-lane graphene superhighway for electrons that could pave the way for ultra-efficient electronics and more. The work revolves around a unique form of pencil lead known as rhombohedral pentalayer graphene.

Long Ju is an assistant professor in the MIT Department of Physics and corresponding author of the paper. He explains, “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.”

Smooth commute for electrons

The phenomenon discovered by the team is similar to cars traveling down an open turnpike as opposed to those moving through neighborhoods.

In regular materials, electrons can be stopped or slowed by other factors, much like cars in a neighborhood can be disrupted by abrupt stops or U-turns. However, in rhombohedral pentalayer graphene, electrons can travel unimpeded.

“We found a goldmine, and every scoop is revealing something new,” says Ju, who is also affiliated with MIT’s Materials Research Laboratory. The material was first discovered two years ago by physicists led by Ju.

Birth of the graphene superhighway

In a Nature Nanotechnology paper last October, Ju and colleagues reported the discovery of three important properties arising from rhombohedral graphene.

They showed that it could be topological, allowing the unimpeded movement of electrons around the edge of the material but not through the middle. This resulted in a superhighway, but required the application of a large magnetic field.

In the current work, the team has managed to create the superhighway without any magnetic field.

Tonghang Han is an MIT graduate student in physics and co-first author of the paper. He notes, “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 also supports more electron channels.”

Superhighway powered with rhombohedral graphene

Pencil lead, or graphite, is composed of graphene, a single layer of carbon atoms arranged in a honeycomb-like structure.

Rhombohedral graphene is composed of five layers of graphene stacked in a specific overlapping order.

Ju and colleagues isolated this unique form of 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.

In the current work, the team added a layer of tungsten disulfide (WS2) to the original system.

“The interaction between the WS2 and the pentalayer rhombohedral graphene resulted in this five-lane superhighway that operates at zero magnetic field,” says Ju.

Quantum anomalous hall effect

The phenomenon that allows electrons to travel with no resistance at zero magnetic field in rhombohedral graphene is known as the quantum anomalous Hall effect.

This is different from superconductivity, which does the same thing but happens in very different materials.

Ju notes that although superconductors were discovered in the 1910s, it took around 100 years of research to make them work at higher temperatures necessary for applications.

Similarly, the rhombohedral graphene superhighway currently operates at about 2 Kelvin, or -456 Fahrenheit.

“It will take a lot of effort to elevate the temperature, but as physicists, our job is to provide the insight; a different way for realizing this [phenomenon],” Ju says.

Perseverance and painstaking research pays off

The discoveries involving rhombohedral graphene came as a result of tireless research that wasn’t guaranteed to work.

Han shares, “We tried many recipes over many months, so it was very exciting when we cooled the system to a very low temperature and [a five-lane superhighway operating at zero magnetic field] just popped out.”

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

New era in electron transport

In summary, the discovery of the five-lane electron superhighway in rhombohedral pentalayer graphene marks a significant milestone in the field of physics and electronics.

The tireless efforts of Long Ju, Tonghang Han, and their colleagues at MIT have opened up new possibilities for ultra-efficient, low-power electronic devices.

While there is still a long road ahead to make this technology practical for everyday applications, the physicists have laid the groundwork for a new era in electron transport.

As they continue to explore the properties of this unique form of graphene, we can expect even more exciting breakthroughs in the future.

The five-lane graphene electron superhighway is just the beginning of a journey that could revolutionize the way we think about and design electronic devices.

The full study was published in the journal Science.

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