Heavy fermions emerge at an atomic-layer interface, unlocking new ways to design quantum materials

Researchers at the University of Osaka have captured the first-ever image of a unique heavy-fermion state developing at the edge where a one-atom-thick material meets a metal. Such states are associated with unusual quantum behavior like unconventional superconductivity, and the discovery provides a pathway to engineer novel quantum materials by manipulating their interfaces.

The scientists produced a high-quality, one-atom-thick sheet of ytterbium-copper (YbCu₂) atop a copper crystal and studied electron behavior across the boundary using powerful synchrotron radiation. Their observations indicated that electrons within the atomic layer interacted with freely moving electrons in the copper substrate to create the heavy-fermion state.

Two distinct heavy-fermion states were identified: one confined predominantly within the two-dimensional YbCu₂ layer and another spanning the three-dimensional copper substrate. The latter emerged due to hybridization between localized Yb 4f electrons in the atomic layer and mobile conduction electrons in the underlying copper, providing concrete proof of an interfacial heavy-fermion state.

This accomplishment, detailed in the journal Communications Material, was made possible through persistent efforts to fabricate high-quality materials and measure their electronic characteristics with great precision. The research's lead author, Shin-ichi Kimura, a professor, expressed enthusiasm for the next step: engineering and controlling these heavy-electron states to unlock previously unexplored quantum states, such as unconventional superconductivity.

The findings suggest that the strategic combination of atomic layers and substrates could serve as a novel method for designing quantum materials, allowing for the creation and fine-tuning of new low-dimensional quantum phenomena that are not possible in standard materials.