Toward a New Generation of Heavy-Electron Materials Without Rare Earths

Nicoletta Barolini for Columbia University Artist's impression of an electron moving through a heavy fermion material: due to intense electronic interactions in certain atomic orbitals, the electrons behave as if they are much more massive, which slows their movement through the material.portent comme s’ils étaient beaucoup plus massifs, ce qui ralentit leur déplacement à travers la matière. Nicoletta Barolini for Columbia University.

Heavy fermion materials, discovered around fifty years ago, are metallic compounds in which electrons behave as if they have an effective mass much greater than that of free electrons. These materials are essential for studying strongly correlated electron systems and unconventional superconductivity, with potential applications in various quantum technologies. Traditionally, creating such materials requires the use of rare earth or actinide elements, which are often scarce, radioactive, or challenging to extract. However, a research team led by Luca de’ Medici from the Laboratoire de Physique et d’Étude des Matériaux (LPEM) at ESPCI Paris – PSL has proposed and successfully tested an innovative method to produce heavy fermion materials without relying on these problematic elements.

The researchers’ strategy involves two key steps. First, they select a metallic compound classified as a Hund’s metal, characterized by strong electronic interactions in partially filled atomic orbitals. Second, they substitute certain metallic atoms with others until the material’s conduction bands are nearly half-filled with electrons. At this point, electrons in specific atomic orbitals interact strongly with each other, significantly slowing their motion and causing them to behave as "heavy." This behavior mimics that observed in traditional heavy fermion materials containing rare earths or actinides.

To demonstrate their technique, the team chose a Hund’s metal composed of cesium, iron, and arsenic, and partially replaced iron atoms with chromium atoms. Resistivity, magnetic susceptibility, and thermal expansion measurements conducted by collaborators at the Karlsruhe Institute of Technology revealed increasingly pronounced heavy-electron behavior as the material was doped. These experimental results validate their approach and pave the way for creating other heavy fermion materials without using rare earth or actinide elements.

This breakthrough also represents a significant step toward designing new quantum materials that are more accessible and environmentally friendly. By eliminating dependence on problematic elements, this method could facilitate the development of technologies leveraging the unique properties of heavy fermions, including advanced electronic devices and quantum computing applications. The next steps will involve applying this strategy to a broader range of materials and exploring their potential properties for diverse technological applications.

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References :
Paradigm for Finding d-Electron Heavy Fermions: The Case of Cr-doped CsFe2As2, Matteo Crispino, Pablo Villar Arribi, Anmol Shukla, Frédéric Hardy, Amir-Abbas Haghighirad, Thomas Wolf, Rolf Heid, Michael Merz, Christoph Meingast, Tommaso Gorni, Adolfo Avella, and Luca de’ Medici, Phys. Rev. Lett. 134, (2025)

Editor suggestion APS : https://physics.aps.org/articles/v18/s15

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