Guiding a superconducting future with graphene quantum magic

Superconductors are materials that do not have any resistance to the electrical current. This ability makes them attractive for a variety of applications, including loss-less power cables, electric motors and generators, as well as powerful electromagnets that can be used for magnetic levitating trains. A new class of material, magic-angle twisted bilayer graphene, has been detailed by researchers from Nagoya University.

Low temperatures are required for a material to behave as a superconductor. Most materials enter the phase at extremely low temperatures, which is lower than what is measured in outer space. This limits their practical applications because of the expensive and specialized liquid helium cooling equipment. Superconducting technologies are still in their infancy.

High temperature superconductors, such as some iron and copper-based examples, enter the superconducting phase above the temperature of liquid nitrogen which cools down the system. HTS materials are brittle ceramic materials that can't be made into useful shapes like wires. They are difficult and expensive to make. Physicists like Prof. Kontani and Dr. Onari are looking for new materials that are superconducting.

A new material has been proposed as a potential superconductor. Two layers of carbon arranged in a honeycomb lattice are offset by a magic angle that leads to the formation of a high-order symmetry known as SU(4). As temperature changes, the system experiences quantum fluctuations, like water ripples in the atomic structure, that lead to a novel change in the electronic structure and a reduction in symmetry. The nematic state is a break in the rotation of symmetry, and it has been associated with superconductivity in other materials.

Prof. Kontani and Dr. Onari used theoretical methods to understand the source of the nematic state.

The interference between the valley degrees of freedom and the spin degrees of freedom in a novel degree-of-freedom has not been reported from conventional strongly correlated electron systems. The nematic state increases the transition temperature of twisted bilayer graphene by several degrees.

The results show that the iron-based high temperature superconductor behaves in some ways like a high temperature superconductor, but it also has some exciting properties, such as a net charge loop current giving rise to a magnetic field in a valley state. Increasing the practical applications of these superconductors can be done with the help of the malleability of Graphene. Science and technology are closer to a conducting future that is super with a better understanding of the underlying mechanisms of superconductivity.

The paper "SU(4) Valley + Spin Fluctuation Interference Mechanism for Nematic Order in Magic-Angle Twisted Bilayer Graphene: The Impact of Vertex Correction" was published in the journal Physical Review Letters.

More information: Seiichiro Onari et al, SU(4) Valley+Spin Fluctuation Interference Mechanism for Nematic Order in Magic-Angle Twisted Bilayer Graphene: The Impact of Vertex Corrections, Physical Review Letters (2022). DOI: 10.1103/PhysRevLett.128.066401 Journal information: Physical Review Letters Citation: Guiding a superconducting future with graphene quantum magic (2022, April 19) retrieved 19 April 2022 from https://phys.org/news/2022-04-superconducting-future-graphene-quantum-magic.html This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.