Five-lane electron superhighway could see ultra-efficient electronics

Physicists have used a unique form of graphene – the material in pencil lead – to create a 5-lane “superhighway” for electrons.

The research, published in Science, could be used in developing ultra-efficient electronics.

“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 corresponding author Long Ju, an assistant professor at the Massachusetts Institute of Technology (MIT), US.

Key to the work is a new material discovered by Ju’s team just 2 years ago: rhombohedral pentalayer graphene. Ju describes the material as a “goldmine.”

Graphene is made up of single-atom-thick layers of carbon atoms arranged in a hexagonal pattern. Rhombohedral pentalayer graphene is composed of 5 layers of graphene stacked in a specific overlapping order. The 5 layers are only a few billionths of a metre thick.

Since its discovery, Ju’s team has reported important properties of the material. For example, last October, they showed it could allow the unimpeded movement of electrons around the edge of the material, but not through its middle.

This electron superhighway, however, requires a magnetic field tens of thousands of times stronger than the Earth’s magnetic field.

The new work shows how the superhighway can be created without the need for a magnetic field.

Ju’s team added a layer of tungsten disulphide (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.

It is not the first time an electron superhighway has been created. But Ju’s team has done so in a unique system which is much simpler than others and supports more electron channels.

The superhighway for electrons is equivalent to having a multi-lane motorway for cars compared to driving through busy neighbourhoods where other vehicles may slow down a commute by turning, merging into lanes or performing U-turns.

Allowing the electrons to travel with no resistance is the quantum anomalous Hall effect. It is a different effect to superconductivity, which promises similar advantages for next-generation electronics.

But both phenomena operate well below room temperature. Raising the operating temperature to make an electron superhighway useful in applications will be a critical next step.

“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 realising this,” Ju says.

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