Interfacial heavy fermion formation in a two-dimensional Kondo lattice YbCu2 on Cu(111) substrate

The exchange interaction between a local magnetic moment and itinerant carriers mediated by the Kondo effect is the origin of strongly correlated quantum phenomena. The concept of an interfacial Kondo lattice, exemplified by the moiré Kondo lattice, provides a powerful platform for exploring quantum critical phenomena such as non-Fermi-liquid behavior and unconventional superconductivity in low dimensions, owing to the high tunability and sensitivity of its physical parameters. However, direct observation of interfacial heavy fermions (HF) has remained elusive due to the lack of suitable candidate systems. Here, we present momentum-resolved evidence of interfacial HF formation between a rare-earth-based two-dimensional (2D) Kondo lattice, YbCu2, and a noble-metal Cu(111) substrate, obtained using high-resolution synchrotron-based angle-resolved photoemission spectroscopy. Momentum-resolved measurements unambiguously reveal interfacial HF states arising from hybridization between the Cu(111) metallic band and the Yb 4f orbitals in the topmost YbCu2 layer. Our experimental results establish an alternative degree of freedom for fabricating artificial Kondo lattices in low-dimensional systems. The interplay between local magnetic moments and itinerant carriers via the Kondo effect underpins complex quantum phenomena, yet direct observation of interfacial heavy fermions remains challenging. Here, the authors provide momentum-resolved evidence of interfacial heavy fermion formation in a 2D Kondo lattice, expanding the possibilities for engineering quantum materials with tunable properties.