Direct electrical access to the spin manifolds of individual lanthanide atoms

Lanthanide series atoms are promising candidates for realizing single molecule magnets which remain magnetically stable at elevated temperatures. They are also being explored for their use as qubits both in the solid state and within molecules due to the long phase coherence time of the magnetic f-electrons and especially their nuclear spins. Recently, Electron Spin Resonance combined with the Scanning Tunneling Microscope (ESR-STM) has been developed into a powerful tool to address individual atomic spins on surfaces. However, driving and sensing spin resonance in lanthanide atoms with ESR-STM has remained a challenge due to f-electron shielding by the nonmagnetic valence electrons, which inhibits magnetoresistive sensing required for the technique. On the other hand, rare earths with an open valence shell have been shown to facilitate stronger interactions with tunneling electrons through intra-atomic exchange coupling between the 4f electrons and valence 6s 5d electrons. Here we demonstrate the detection of spin resonance in two different open-shell lanthanide elements adsorbed on a thin insulating film using the STM. For europium, our measurements reveal an unexpectedly rich spectral structure which arises from the combination of a large manifold of electron spin states and nuclear hyperfine interactions which can all be accessed at GHz energy scales. For samarium, a relatively large g factor presents opportunities for magnetic sensing at the atomic scale. Our results demonstrate the ability to drive and sense spin resonance of individual rare earth atoms with atomic resolution while providing a route to studying uncommon open valence shell lanthanide species.

[1] Czap et al. (2024) https://doi.org/10.48550/arXiv.2408.11335