To reach superconductivity layer by layer

Schematic representation of hopping and on-site parameters γi and δ (left) and corresponding values ​​used in current calculations (right). Credit: Physical examination B (2023). DOI: 10.1103/PhysRevB.107.104502

Imagine a sheet of material only one layer of atoms thick – less than a millionth of a millimetre. Although this may sound fantastic, such a material does exist: it is called graphene and it is made of carbon atoms in a honeycomb arrangement. First synthesized in 2004 and then soon hailed as a substance with amazing properties, scientists are still working to understand it.

Postdoc Areg Ghazaryan and Professor Maksym Serbyn at the Institute of Science and Technology Austria (ISTA) together with their colleagues Dr. Tobias Holder and Professor Erez Berg from the Weizmann Institute of Science in Israel have been studying graphene for years and have now published their latest findings about its superconductivity characteristics in a research article in the journal Physical examination B.

“Multilayer graphene has many promising qualities ranging from highly tunable band structure and special optical properties to new forms of superconductivity – meaning being able to conduct electrical current without resistance,” explains Ghazaryan.

“In our theoretical model, we continue our work with multilayer graphene and look at different possible arrangements of different graphene sheets on top of each other. There we found new possibilities for creating so-called topological superconductors.” In their study, the researchers simulated on a computer what happens when you stack a few layers of graphene sheets on top of each other in certain ways.

An electronic beauty contest

“It’s like a big beauty contest among the different configurations of stacked sheets of graphene to find the best one,” adds Serbyn. “In it, we look at how the electrons moving in the multilayer graphene behave.”

Depending on how the different layers of graphene are displaced relative to each other and how many layers there are, the positively charged nuclear cores of the carbon atoms in the honeycomb lattice create different environments for the electrons around them. The negatively charged electrons are attracted to the nuclei and repelled by each other.

“We started by investigating realistic models that consider only a single electron interacting with the graphene cores. When we found a promising approach, we added the more complicated interactions between many electrons,” explains Ghazaryan. With this approach, the researchers confirmed the existence of the exotic form of topological superconductivity.

Looking for nature’s feedback

This type of theoretical research lays the foundation for future experiments that will create the simulated graphene systems in a laboratory to see if they really behave as predicted. “Our work helps experimentalists design new setups without having to try out every configuration of graphene layers,” says Ghazaryan. “Now theoretical research will continue while experiments will give us feedback from nature.”

While graphene has slowly found applications in research and technology – such as carbon nanotubes – its potential as a topological superconductor for electricity is only beginning to be understood. Serbyn adds, “We hope to one day be able to fully describe this type of material at a quantum mechanical level, both for the intrinsic value of scientific investigation of the fundamental properties of matter and the many potential applications of graphene.”

More information:
Areg Ghazaryan et al, Multilayer graphenes as a platform for interaction-driven physics and topological superconductivity, Physical examination B (2023). DOI: 10.1103/PhysRevB.107.104502

Journal information:
Physical examination B

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