Researchers from Uppsala University, together with other collaborators, have discovered a new two-dimensional quantum material in a recently published study. Nature. This groundbreaking material consists of atomically thin layers of cerium, silicon, and iodine (CeSiI), the first example of a two-dimensional material with heavy fermions.

“Electrons in CeSiI behave as if they had 100 times more mass than electrons in ordinary materials. That’s why they are called heavy fermions. The peculiarity of CeSiI is that this effective mass is anisotropic and depends on the direction in which the electrons in the atomic layers move,” says one of the Uppsala researchers behind the study. one of them, Chin-Shen Ong.

The research is the result of a collaboration between materials theory researchers at Uppsala University and researchers at Columbia University in the United States. The main topic for materials researchers from Uppsala University was the theoretical study of the quantum properties of electrons in the material.

Background and importance of heavy fermions

Heavy fermionic compounds are a class of materials in which electrons interact extremely strongly with each other. They also coordinate their movements in so-called quantum fluctuations. This interaction causes electrons to behave as if they had 100 or 1000 times more mass than electrons in ordinary materials. These quantum fluctuations are believed to play an important role in a number of hitherto unexplained quantum phenomena, such as unusual superconductivity and magnetism, in which an electric current can pass through a material without losing energy.

Research into materials with heavy fermions has been ongoing for decades, but until now the main focus has been on materials in which atoms are tightly packed in a three-dimensional structure. In the 1970s, researchers at Uppsala University focused on cerium-based materials with great success. But the new material synthesized in the Columbia University laboratory is unique because it has a 2D-like crystal structure with clearly separated atomic layers. The layers consist of cerium, silicon, and iodine (CeSiI) and are the first example of a 2D material with heavy fermions.

“Thanks to this discovery, we now have a significantly improved materials platform for investigating correlated electronic structures. 2D materials are like a LEGO set. Our partners are already working on adding layers of other 2D materials to create a new material with tuned quantum properties,” says Chin. -Shen Ong.