Description

Single lanthanide atoms and molecules are promising candidates for atomic data storage and quantum logic due to the long lifetime of their magnetic quantum states. Accessing and controlling these states through electrical transport requires precise knowledge of their electronic configuration at the level of individual atomic orbitals, especially of the outer shells involved in transport. However, no experimental techniques have so far shown the required sensitivity to probe single atoms with orbital selectivity. Here we resolve the magnetism of individual orbitals in gadolinium and holmium single atoms on magnesium oxide thin films grown on Ag(100) single crystals. We realized this investigation combining X-ray magnetic circular dichroism with multiplet calculations and density functional theory. Using orbital sensitivity of the X-ray technique, we reveal a charge transfer mechanism leading to an unconventional singly ionized configuration for these lanthanide atoms. Our work identifies the role of the valence electrons in determining the quantum level structure and spin-dependent transport properties of lanthanide-based nanomagnets.