Kondo singlets and interactions observed in a magnetically doped 2D metal.

Pd₅AlI₂ is a unique two-dimensional metal that features a decorated checkboard PdAl lattice in which hopping between Pd d orbitals mediated by Al p orbitals determines the electronic structure. This decorated checkerboard structure results in a flat band arising from geometric interference. The wavefunctions of this flat band can be written in a real space basis via compact localized states (CLS). In this study, we report the scanning tunneling microscopy/spectroscopy study of Pd₅AlI₂ while replacing Pd with defect atoms that have unpaired 3d electrons. The interaction between the localized defect spins and the conduction electrons forms a Kondo singlet as observed in the low-temperature density of states (DOS). Its lateral distribution manifests as a spatially extended molecular d orbital, shedding light on the CLS in the presence of a magnetic defect. When these defects are brought together, the interaction between them dramatically modifies the DOS near the Fermi level resulting in asymmetric or split peaks depending on the alignment of such defects. These phenomena arise from a delicate interplay between exchange interactions and conduction electron screening by CLS states of the flat band. Our experiments demonstrate an interesting platform to study Kondo physics in a 2D metal system which is air-stable and mechanically exfoliable.