January 27, 2024 -- Two-dimensional quantum materials provide a unique platform for new quantum technologies, because they offer the flexibility of combining different monolayers featuring radically distinct quantum states. Different two-dimensional materials can provide building blocks with features like superconductivity, magnetism, and topological matter. But so far, creating a monolayer of heavy-fermion Kondo matter – a state of matter dominated by quantum entanglement – has eluded scientists. Now, researchers at Aalto University have shown that it’s theoretically possible for heavy-fermion Kondo matter to appear in a monolayer material, and they’ve described the microscopic interactions that produces its unconventional behavior. These findings were published on February 23, 2024 in Nano Letters.

“Heavy-fermion materials are promising candidates to discover unconventional topological superconductivity, a potential building block for quantum computers robust to noise,” says Adolfo Fumega, the first author of the paper and a post-doctoral researcher at Aalto University.

These materials can feature two phases: one analogous to a conventional magnet, and one where the state of the system is dominated by quantum entanglement, known as the heavy-fermion Kondo state. At the transition between the magnetic phase and the heavy-fermion state, macroscopic quantum fluctuations appear, leading to exotic states of matter including unconventional superconducting phases.

The material analyzed in the paper is a monolayer CeSiI, a compound that has been recently isolated in the ultrathin limit. Using a combination of many-body and quantum chemistry methods, the researchers showed the nature of competing quantum magnetic interactions in the material, demonstrating that such competition leads to an unconventional quantum entangled state. Furthermore, they showed that the quantum magnetism in this material is dominated by relativistic effects, leading to a subatomic magnetic structure radically different from other two-dimensional materials.

“The discovery of a heavy-fermion quantum material monolayer establishes a fundamental building block for quantum devices,” says Jose Lado, an assistant professor at Aalto University who also heads the Correlated Quantum Materials research group.

Bulk heavy-fermion materials are greatly challenging from the material science point of view, and making devices out of them is a nearly impossible task. With a purely two-dimensional heavy-fermion quantum material and the flexibility of stacking van der Waals layers, a whole new family of quantum devices based on exotic heavy-fermion Kondo phenomena may be developed, opening up yet unexplored directions in quantum technologies.