Orbital selective 5f electron character, indication of Kondo effect, and subatomic features of single uranium atoms

In actinide-based materials, the multiplicity of $5f$ orbitals provides a rich setting to elucidate the large and outstanding issues of the competition and interplay among different channels of interactions. Among them, the dual character of $5f$ electrons has been studied in some $5f$ electron Kondo lattice compounds. Here, by using scanning tunneling microscopy/spectroscopy (STS), we present the indication of Kondo effect driven by $5f$ electrons and subatomic features of single U atoms on graphene/6H-SiC(0001), ${\mathrm{Cu}}_{2}\mathrm{N}/\mathrm{Cu}(100)$, and Bi(110). For all three systems, an asymmetric-dip spectral feature can be observed around the Fermi energy, which is an indication of Kondo resonance in STS. The size of the ``screening cloud'' for single U atoms on Bi(110) is much larger than that observed on graphene/6H-SiC(0001) and ${\mathrm{Cu}}_{2}\mathrm{N}/\mathrm{Cu}(100)$, indicating the $5f$ electrons of single U atoms on Bi(110) are more itinerant than that on the other two substrates. In addition to the asymmetric spectrum feature around the Fermi energy, various subatomic spectrum features are also observed from the $dI/dV$ maps of U atoms on different substrates. Further density-functional theory calculations show that these distinct subatomic features arise from the orbital selective hybridizations between U atoms and the substrates. Our results present the distinct observation of the orbital selective $5f$ electron character, indication of Kondo effect, and together with the subatomic features of individual $5f$ impurity magnetic atoms adsorbed on nonmagnetic surfaces.