Researchers turn 'magic angle graphene' into insulator or superconductor by applying an electric voltage

Researchers at ETH Zurich, led by Klaus Ensslin and Thomas Ihn at the Laboratory for Solid State Physics, have succeeded in turning specially prepared graphene flakes either into insulators or into superconductors by applying an electric voltage. This technique is even said to work locally, meaning that in the same graphene flake regions with completely different physical properties can be realized side by side.

A material-keyboard made of graphene imageThe material keyboard realized by the ETH Zurich researchers. Image by ETH Zurich/F. de Vries

The material Ensslin and his co-​workers used is known as “Magic Angle Twisted Bilayer Graphene”. The starting point for the material is graphene flakes - the researchers put two of those layers on top of each other in such a way that their crystal axes are not parallel, but rather make a “magic angle” of exactly 1.06 degrees. “That’s pretty tricky, and we also need to accurately control the temperature of the flakes during production. As a result, it often goes wrong,” explains Peter Rickhaus, who was involved in the experiments.

Researchers take a step towards achieving topological qubits in graphene

Researchers from Spain, Finland and France have demonstrated that magnetism and superconductivity can coexist in graphene, opening a path towards graphene-based topological qubits.

Schematic illustration of the interplay of magnetism and superconductivity in a graphene grain boundary imageSchematic illustration of the interplay of magnetism and superconductivity in a graphene grain boundary, a potential building block for carbon-based topological qubits Credit: Jose Lado/Aalto University

In the quantum realm, electrons can behave in interesting ways. Magnetism is one of these behaviors that can be seen in everyday life, as is the rarer phenomena of superconductivity. Intriguingly, these two behaviors are often antagonists - the existence of one of them often destroys the other. However, if these two opposite quantum states are forced to coexist artificially, an elusive state called a topological superconductor appears, which is useful for researchers trying to make topological qubits.

Researchers produce extremely conductive graphene-enhanced hydrogel for medical applications

An interdisciplinary research team of the Research Training Group (RTG) 2154 "Materials for Brain" at Kiel University (CAU) has developed a method to produce graphene-enhanced hydrogels with an excellent level of electrical conductivity. What makes this method special is that the mechanical properties of the hydrogels are largely retained. The material is said to have potential for medical functional implants, for example, and other medical applications.

"Graphene has outstanding electrical and mechanical properties and is also very light," says Dr. Fabian Schütt, junior group leader in the Research Training Group, thus emphasizing the advantages of the ultra-thin material, which consists of only one layer of carbon atoms. What makes this new method different is the amount of graphene used. "We are using significantly less graphene than previous studies, and as a result, the key properties of the hydrogel are retained," says Schütt about the current study, which he initiated.

Researchers find surprising electron interaction in ‘magic-angle’ graphene

A research team, led by Brown University physicists, has found a new way to precisely probe the nature of the superconducting state in magic-angle graphene. The technique enables researchers to manipulate the repulsive force - the Coulomb interaction - in the system. In their recent study, the researchers showed that magic-angle superconductivity grows more robust when Coulomb interaction is reduced, which could be an important piece of information in understanding how this superconductor works.

"This is the first time anyone has demonstrated that you can directly manipulate the strength of Coulomb interaction in a strongly correlated electronic system," said Jia Li, an assistant professor of physics at Brown and corresponding author of the research. "Superconductivity is driven by the interactions between electrons, so when we can manipulate that interaction, it tells us something really important about that system. In this case, demonstrating that weaker Coulomb interaction strengthens superconductivity provides an important new theoretical constraint on this system."

Researchers create tunable superconductivity in magic-angle twisted trilayer graphene

When two sheets of graphene are stacked atop each other at just the right angle, the layered structure morphs into an unconventional superconductor, allowing electric currents to pass through without resistance or wasted energy. This “magic-angle” transformation in bilayer graphene was observed for the first time in 2018 in the group of Pablo Jarillo-Herrero at MIT. Since then, scientists have searched for other materials that can be similarly twisted into superconductivity, but for the most part, no other twisted material has exhibited superconductivity other than the original twisted bilayer graphene.

Stacking order imageIllustrations of A-tw-A stacking (a) and A-tw-B stacking (b). Image from Nature

In a recent paper, Jarillo-Herrero and his group reported observing superconductivity in a sandwich of three graphene sheets, the middle layer of which is twisted at a new angle with respect to the outer layers. This new trilayer configuration reportedly exhibits superconductivity that is more robust than its bilayer counterpart.