When two mesh screens are overlaid, beautiful patterns appear when a screen is offset. These "moiré patterns" have long fascinated artists, scientists and mathematicians and found applications in the areas of printing, fashion and banknotes.
Now, a team led by Rutgers has paved the way for solving one of the most enduring puzzles in material physics by discovering that electrons organize into stripes in the presence of a moiré pattern in graphene, like soldiers in formation.  Their results, published in the journal Nature may be helpful in the search for quantum materials such as superconductors that work at room temperature. Such materials would drastically reduce energy consumption by making power transmission and electronic devices more efficient.
"Our findings provide a substantial clue to the mystery that connects a form of graphene, the so-called twisted bilayer graph, to superconductors that could work at room temperature," said lead author Eva Y. Andrei, a senior professor Physics and Astronomy Council at the School of Arts and Sciences, Rutgers University, New Brunswick.
Graphene – an atomically thin layer of graphite used in pencils. is a network of carbon atoms that looks like a honeycomb. It's a great electricity conductor and much stronger than steel.
The team led by Rutgers investigated twisted bilayer graphene generated by superposition of two layers of graphene and slight misalignment. This creates a "twist angle" that results in a moiré pattern that changes rapidly as the twist angle changes.
In 2010, Andrei discovered that moiré patterns made with twisted bilayer graphene are not only pretty, but also have a dramatic effect on the electronic properties of the material. Namely, the moiré pattern slows down the electrons that conduct electricity into graphene and pass each other at high speed.
At a twist angle of about 1.1 degrees – the so-called magic angle – these electrons almost stop. The sluggish electrons begin to see and interact with their neighbors to move in lockstep. This gives the material amazing properties like superconductivity or magnetism.
Using a technique invented by Andrei's group to study twisted bilayer graphs, the team discovered a state in which the electrons organize into stripes that are robust and hard to break.
"Our team found a close similarity between this feature and similar observations in high-temperature superconductors provide new evidence of the deep connection that underlies these systems and open the way to solve their constant puzzle," said Andrei.
Experiments explore the secrets of "magic" angle superconductors
Yuhang Jiang et al. Charge Order and Cracked Rotation Symmetry in Magically Angled Double-Layer Graphs, Nature (2019). DOI: 10.1038 / s41586-019-1460-4
Physicists discover graphene that could contribute to the development of superconductors (2019, 1 August)
retrieved on August 1, 2019
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