Superconductivity in single-layer graphene? IMDEA Nanociencia researchers suggest it is possible

06.02.2025

The ideal crystalline structure of graphene is a hexagonal grid. Image: AlexanderAlUS (CC-BY-SA 3.0).

A theoretical model developed at IMDEA Nanociencia is now applied to graphene monolayers.
The model, based on electronic interactions, is applied to predict superconductivity in a single layer of graphene.

Madrid, 6th February, 2025. Since graphene was first isolated in 2004, researchers have continued studying this exotic material and its extraordinary properties. Graphene, a single layer of hexagonally arranged carbon atoms, is 200 times stronger than steel while being light and flexible; It is also an excellent conductor of electricity and heat, while also being optically transparent. Although its conductivity is good, the researchers have wondered if it would be possible to observe superconductivity, a phenomenon by which electric charges would move with zero resistance through the material. Since the discovery of superconducting phases in graphene bilayers, the scientific community has renewed its interest in the search for superconductivity in other systems. However, the question of whether it would be possible to observe superconductivity in a single graphene layer is still an unknown that is not entirely resolved.

In a recent work, researchers led by Pierre Pantaleón and José Silva at IMDEA Nanociencia suggest that single-layer graphene may be superconducting. Although previous studies had already raised this possibility, the study has employed a theoretical approach supported by numerical simulations and experimental evidence to demonstrate that superconductivity in a single graphene layer is feasible.

The graphene band diagram is characterized by the so-called "Dirac cone", a place where excited (conduction) and unexcited (valence) states converge, forming a characteristic structure that gives rise to exotic quantum phenomena. Far from that part of the diagram, at high energies, a multitude of flat bands with high density of states converge. Superconductivity was predicted phenomenologically in this area of the diagram (González 2008, Chubukov 2012), although at that time the necessary computational capacity to make a complete analysis was not available.

In a theoretical-experimental collaboration between IMDEA Nanociencia (Spain), the Institute of Physics of the UNAM (Mexico) and the MPI Festkörperforschung (Germany), researchers have used a graphene system doped with terbium atoms. This doping is essential for injecting electrons into graphene without altering its electronic structure. In this system, terbium atoms are deposited on or below the graphene monolayer, without replacing the carbon atoms in the hexagonal lattice. In other words, terbium atoms act only as electron donors, preserving the crystal structure of graphene.

Ulrich Starke's group (MPIF) managed to heavily dope graphene with terbium atoms and characterize its band structure using an experimental technique, Angle-Resolved Photoemission Spectroscopy (ARPES). From these experimental data, Pierre Pantaleón and his team at IMDEA Nanociencia performed a numerical analysis, determining that superconductivity could theoretically arise at a critical temperature of 600 milliKelvin (-272.55 °C). In addition, they found that this state is stable against fluctuations, which reinforces their hypothesis.

In general, to describe superconductivity in graphene-based materials two main theoretical frameworks can be considered. The first is the conventional theory, which is based on a coupling mechanism between electrons that occurs thanks to phonons (vibrations of the crystal lattice). The second is the unconventional framework, in which superconductivity arises from electronic interactions without the mediation of phonons. In recent years, the availability of new experimental data has generated a debate about the feasibility of the conventional phonon-based mechanism in graphene systems, favouring instead an explanation in terms of electronic interactions. One of the first unconventional models applied to graphene multilayers was developed in 2021 by Prof. Francisco Guinea's group at IMDEA Nanociencia. Importantly, conventional and unconventional mechanisms are difficult to reconcile within the same theoretical framework, suggesting that superconductivity in graphene should be attributed primarily to one of them. In this context, the new work led by Dr. Pierre Pantaleón provides additional evidence in favour of an unconventional mechanism as a possible origin of superconductivity in different graphene structures.

Pierre is enthusiastic: "It was an open problem since 2010 and curiosity has led us to describe in detail a new interesting phenomenon that had not been demonstrated to date." Saúl Herrera (UNAM), first author of this work, conceived the original idea of analysing this system in detail. Now, once the phenomenon has been predicted, its empirical demonstration is pending.

The work, published in ACS Nano (DOI: 10.1021/acsnano.4c12532), opens up the possibility of realizing and studying superconductivity in a single graphene layer, which could not only expand our understanding of the fundamental mechanisms of superconductivity, but also lay the groundwork for a new generation of advanced graphene-based technologies.

This work is a collaboration between scientists led by Dr. Pierre Pantaleón and Dr. José Silva at the Madrid Institute for Advanced Studies in Nanoscience (Spain); Prof. Gerardo Naumis at the National Autonomous University of Mexico; Prof. Ulrich Starke at the Max Planck Institute for Research in Solid Bodies (Germany); and Lund University, and has been partially funded by the Severo Ochoa accreditation to IMDEA Nanoscience (CEX2020-001039-S).

Glossary:

Graphene: sheet of carbon atoms arranged in a regular hexagonal pattern, atomically thick.
Superconductivity: The ability to conduct electric current without resistance or loss of energy. The strength of a superconducting material drops sharply to zero when the material is cooled below its critical temperature.
Doping: In the field of electronics, doping refers to the technique of varying the number of electrons in a material by adding atoms of another element, which would modify the electrical properties of the parent material.

Reference:

Saúl A. Herrera, Guillermo Parra-Martínez, Philipp Rosenzweig, Bharti Matta, Craig M. Polley, Kathrin Küster, Ulrich Starke, Francisco Guinea, José Ángel Silva-Guillén, Gerardo G. Naumis, and Pierre A. Pantaleón. Topological Superconductivity in Heavily Doped Single-Layer Graphene. ACS Nano 2024 18 (51), 34842-34857. DOI: 10.1021/acsnano.4c12532

Link to IMDEA Nanociencia repository: https://hdl.handle.net/20.500.12614/3844

Contact:

Pierre Pantaleón
This email address is being protected from spambots. You need JavaScript enabled to view it.

José Á. Silva Guillén
First-Principles Modelling for Quantum Materials Group
https://nanociencia.imdea.org/first-principles-modelling-for-quantum-materials/home

Dissemination and Communication Office - IMDEA Nanociencia
divulgacion.nanociencia [at]imdea.org

Source: IMDEA Nanociencia.

IMDEA Nanociencia Institute is a young interdisciplinary research Centre in Madrid (Spain) dedicated to the exploration of nanoscience and the development of applications of nanotechnology in connection with innovative industries.