Scientists identify quantum geometry as essential to this process that Electricity move without using its energy. Researchers have presented new evidence (Discover the magic of the “magic corner” of superconductivity) showing how graphene, when bent in a specific direction, can become a material that makes electricity move without using its energy.
In a study published yesterday (Feb. 15, 2023) in the journal Nature, a team of scientists from Ohio State University reported on the key role that quantum geometry plays in helping twisted graphene to become a leader.
Graphene is a single layer of carbon, the same type found in pencils.
In 2018, scientists at the Massachusetts Institute of Technology discovered that, under the right conditions, graphene can become a catalyst if one layer of graphene is placed on top of another and rotated ‘clouds in one direction – 1.08 degrees – to create a twist, bilayer graphene.
Since then, scientists have been studying this twisted graphene and trying to understand how this “magic part” works, said Marc Bockrath, professor of physics at Ohio State and co-author of the Nature paper.
“The conventional theory of superconductivity doesn’t work in this situation,” Bockrath said. “We did a series of research to understand why this was such a big deal.”
In a typical metal, high-speed electrons are responsible for conductivity.
But the curved bilayer graphene has an electronic structure known as a “flat band” in which electrons move very slowly – in fact, the speed is close to zero if the angle is exactly at the magic angle .
According to the traditional theory of superconductivity, such fast-moving electrons should not be able to conduct electricity, said the paper’s co-author Jeanie Lau, also a professor of physics at Ohio State.
Haidong Tian, the first author of the paper and a student in Lau’s research department, used a device so close to magic that it is almost a standard practice of condensed matter physics. electrons stopped. However, the sample showed superconductivity.
“It’s a puzzle: how do electrons slowly conduct electricity, but not alone? It’s remarkable,” said Lau.
In their experiments, the research team demonstrated a slower electron speed and provided measurements of electron motion greater than previously available.
They also found the first clues about what makes graphene so special.
“We can’t use the speed of electrons to explain how twisted graphene works,” Bockrath said. “Instead, we have to use quantum geometry.”
As with all things, quantum geometry is complex and incomprehensible. But the results of this study are related to the fact that the electron is not only a particle, but also a wave – and thus has a wave function.
“The geometry of quantum wavefunctions and flat bands, as well as the interaction between electrons, leads to the flow of electric current without dissipation in bilayer graphene,” said co-author Mohit Randeria, professor of physics at Ohio State. said.
“We found that the equation can explain maybe 10% of the superconductivity signal we found. Our experiments show that quantum geometry is 90% of what makes it superconductive,” said Lau.
The best effect of this material can be seen in experiments at very low temperatures. The ultimate goal is to be able to understand the factors that lead to high temperatures, which can be useful in global applications, such as electrical transmission and communication, Bockrath said.
“It will have a huge impact on society,” he said. “It’s far from the case, but this discovery really takes us another step to understanding how it can happen.”
