2023-05-30 10:45:07
A new theory explains superconductivity in spun graphene trilayers. The study lays the foundations for understanding the mechanisms of certain unconventional superconducting materials
Five years ago, researchers from the Massachusetts Institute of Technology (MIT) in the United States, led by the Valencian physicist Pablo Jarillo-Herrero, discovered that it is possible to change the electronic properties of graphene by altering in a very precise, almost magical way, the angle of rotation between two of its layers. Graphene, a material made up of a group of carbon atoms that are positioned hexagonal, thus became a superconductor, capable of transporting electricity without dissipating energy, something very peculiar.
“Superconductivity, a common phenomenon in metals such as mercury, lithium or titanium when they are subjected to low temperatures, can be understood by the pairing of electrons (in pairs called Cooper pairs) due to the interaction of electrons with vibrations or phonons of the atomic lattice. However, in the rotated graphene layers, there is evidence that superconductivity cannot be supported by such a conventional mechanism, which until now has made theoretical efforts to find an explanation difficult,” explains José González Carmona, a researcher at the Institute of Structure de la Materia (IEM), attached to the Higher Council for Scientific Research (CSIC) in Spain.
Now, González Carmona and Tobias Stauber, from the Institute of Materials Science of Madrid (ICMM) dependent on the CSIC, propose a theoretical construction that includes an unconventional mechanism of superconductivity, based on the electron-electron interaction itself, dominant in carbon materials like graphene. This type of pairing between electrons confers great stability, since it prevents the Cooper pairs from being destroyed by certain magnetic fields, something that can happen with conventional superconductivity. “The idea that we propose is groundbreaking for these carbon materials, and leads to a superconductivity with a special character, called the Ising type in similar two-dimensional systems”, highlights González Carmona.
Basic structure of graphene, a material consisting of a sheet composed of hexagonal positioned carbon atoms. (Image: NIH 3D)
The scientists, who have used the resources of the Galician Supercomputing Center (CESGA) and the Drago supercomputing cluster, installed on the CSIC’s central campus in Madrid, have used computational tools to design this highly reliable and capable method. to describe the total number of atoms (around 8,000 in the unit cell of rotated trilayers). “The model with which we have treated the rotated graphene layers, which has allowed us to capture details at the atomic level, has been essential in finding the key to the new superconductivity mechanism that we propose”, indicates Stauber.
Towards superconductors at room temperature
As soon as Jarillo-Herrero’s discovery was made known, the scientific community observed similarities between the superconductivity in the rotated graphene layers and the behavior of another type of material: high-temperature superconducting copper oxides. “These materials have been defying convincing theoretical explanation for more than 30 years. Both in this case and in that of graphene, we are talking about materials that imply new physics, so it is important to find the path towards a new paradigm with which to encompass a set of systems where it is the electron-electron interaction that dictates the properties, instead of the electron-phonon interaction”, indicates Stauber.
Currently, superconducting materials are still far from easily accessible temperatures, a condition that makes it difficult for them to fully reach the market. This is why condensed matter physicists continue to seek to achieve superconductivity at room temperature.
“Our theoretical construction -says González Carmona- may open the way towards understanding a new superconductivity mechanism, which escapes conventional description. This new physics is called for by copper oxides, which were once seen as a possibility of achieving superconductivity at room temperature. This continues to be a very attractive goal within condensed matter physics, which may require new paradigms like the one we propose with our research”.
The study is titled “Ising superconductivity induced from spin-selective valley symmetry breaking in twisted trilayer graphene”. And it has been published in the academic journal Nature Communications. (Source: Alda Ólafsson / CSIC)
#mystery #superconductivity #graphene #architectures