Visualizing the Kondo lattice and heavy fermion emerging in a Pr-based ferromagnet

In conventional heavy fermion compound that hosts a Kondo lattice, the hybridization between the itinerant electron and localized f-electron generates heavy electron quasiparticles that often quenches the magnetic order. Previous studies suggest co-existence of Kondo lattice and magnetic order in U based 5f-electron systems possibly owning to the dual character of the 5f electrons. In the more localized 4f-electron system that has more than single electron in the f orbitals, magnetic order co-existing with Kondo lattice behavior is much rarer to find. Here, by using low-temperature scanning tunneling microscopy/spectroscopy (STM/S), we present evidence of Kondo lattice behavior persisting within the robust ferromagnet phase (T_c=41 K) of a praseodymium-based material. Within the ferromagnetic phase, pronounced Fano line shapes, characteristic of a Kondo lattice, are observed in the local density of states across the scanning field-of-view. Furthermore, concurrent high-resolution quasiparticle interference (QPI) imaging simultaneously reveals rapid evolution of heavy-quasiparticle bands near the hybridization gap and the slowly evolving light-quasiparticle bands. Our results demonstrate the rare duality of Kondo entanglement and magnetism in a new 4f-electron-based rare-earth compound, creating a quantum playground where localized 4f moments simultaneously participate in magnetic ordering and conduction electron hybridization.