Researchers from the Institute of Materials Science of Madrid (ICMM), CSIC, have found why electronic cascade systems in rotated graphene bilayers with magic angle. His discovery just published in the magazine nature communicationrefutes previous theories about this intriguing magic angle property of graphene bilayers.
A little over five years ago, it was discovered that by rotating one sheet of graphene relative to the other by just 1.1 degrees (the so-called “magic angle”), this material acquired new and surprising properties due to the interaction of its electrons. : Unexpected insulating and superconducting states have been observed. Later they met dramatic changes in the energy of the electrons in the form of waterfalls. All of these phenomena opened up a new field of research, and these systems (simple a priori, since they are only carbon-based) exhibit a greater variety of electronic states than any other.
“In the first interpretations of the cascades, it was believed that they had to do with ordered states, such as magnetic states detected in the system at very low temperatures, on the order of 5 Kelvin, but these cascades are much more resilient and survive.” Temperatures of several tens of Kelvin (1 K corresponds to -272.15 °C),” explains Leni Bascones, researcher at ICMM and author of the study. His work shows that the origin of this phenomenon is different.
In particular, this study shows that cascades are expected with no order required. “We are not saying that there is no order in magic angle bilayers, that has been observed, but at lower temperatures,” he points out. Maria Jose CalderonResearcher at ICMM and also author of the article.
The key to this research that has significant connotations for Study materials such as unconventional superconductors, lies in the technique used for its theoretical description: dynamic mean field theory combined with Hartree calculations. “It’s the most advanced numerical technique used to date to study the type of effect we’re looking for,” Bascones points out. “It’s a very complex problem, because in solids there are many interacting electrons and the collective behavior arises, which means you can’t understand it trivially as the sum of the behavior of individual electrons,” emphasizes Calderón.
It is a very complex problem because in solids there are many interacting electrons and collective behavior arises.
“When they started to discover the properties of these twisted graphene bilayers, they wanted to see if they could be related to high-temperature superconductors,” explains Bascones.
Although it was initially assumed that the phenomenology behind these materials had no bearing on graphene bilayers, “lets say precisely that…” underlying origin of these cascades is related to the type of physics that occurs in other correlated systems, such as the superconductors mentioned above. This could be the key to understanding how these superconductors work, which in turn are essential for technological goals such as efficient energy transmission or quantum computing.
Reference:
A Datta, MJ Caldeón, A Camjayi, E Bascones:”Heavy quasiparticles and cascades without symmetry breaking in twisted bilayer graphene”. nature communication.
