Moiré pattern in graphene causes electrons to form stripes

When two mesh screens are overlaid, beautiful patterns appear when one screen is offset from the other. These ‘moiré patterns’ have long intrigued artists, scientists and mathematicians, and have found applications in printing, fashion and banknotes.

Now, a team led by researchers at Rutgers University has gone some way towards solving one of the most enduring mysteries in materials physics, by discovering that in the presence of a moiré pattern in graphene electrons organize themselves into stripes, like soldiers in formation.

These findings, reported in a paper in Nature, could help in the search for novel quantum materials, such as superconductors that work at room temperature. Such materials would dramatically reduce energy consumption by making power transmission and electronic devices more efficient.

"Our findings provide an essential clue to the mystery connecting a form of graphene called twisted bilayer graphene to superconductors that could work at room temperature," said senior author Eva Andrei, a professor in the Department of Physics and Astronomy at Rutgers University-New Brunswick.

Graphene comprises a layer of carbon atoms arranged like a honeycomb; it's a great conductor of electricity and much stronger than steel. The Rutgers-led team studied twisted bilayer graphene, created by superimposing two layers of graphene and slightly misaligning them. This creates a ‘twist angle’ that results in a moiré pattern that changes rapidly as the twist angle changes.

In 2010, Andrei's team discovered that, in addition to being pretty, moiré patterns formed with twisted bilayer graphene have a dramatic effect on the electronic properties of the material. This is because the moiré pattern slows down the electrons that conduct electricity in graphene, which usually zip past each other at great speeds.

At a twist angle of about 1.1° – the so-called magic angle – these electrons come to an almost dead stop. The sluggish electrons start seeing each other and interacting with their neighbors to move in lockstep. As a result, the material acquires amazing properties such as superconductivity or magnetism.

Using a technique invented by Andrei's group to study twisted bilayer graphene, the team discovered a state where the electrons organize themselves into stripes that are robust and difficult to break.

"Our team found a close resemblance between this feature and similar observations in high-temperature superconductors, providing new evidence of the deep link underlying these systems and opening the way to unraveling their enduring mystery," Andrei said.

This story is adapted from material from Rutgers University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.