NOVEMBER 1, 2022
Jinkyung Kim, Kyungju Noh, Yi Chen, Fabio Donati, Andreas J. Heinrich, Christoph Wolf, and Yujeong Bae
Nano Letters (2022)
Hyperfine interactions between electron and nuclear spins have been widely used as a sensitive probe to the local chemical environment through spatial identification of nuclear spins. With the nuclear spins identified, the full determination of hyperfine interactions along different principal axes in turn offer unique insight into the electronic ground-states of the paramagnetic centers. However, traditional ensemble measurements of hyperfine interactions average over a macroscopic number of spins with different geometrical locations and nuclear isotopes. In this work, the researchers used electron spin resonance (ESR) technique combined with scanning tunneling microscopy (STM) in vector magnetic fields to measure the hyperfine interactions of a single hydrogenated-Ti atom on 2 monolayers of MgO(100) on the Ag(100) substrate. Together with atom manipulation, the researchers observed a large anisotropy of about 67% in the hyperfine interactions. Identifying the isotropic and anisotropic contributions in the hyperfine interaction, the electronic ground states were carefully determined as supported by the density functional theory calculations. This work highlights the power of ESR-STM-enabled single-atom hyperfine spectroscopy as a powerful tool in revealing ground-state electronic structures and atomic-scale chemical environments with several tens of nano-electronvolts resolution.
Hyperfine interactions have been widely used in material science, organic chemistry, and structural biology as a sensitive probe to local chemical environments. However, traditional ensemble measurements of hyperfine interactions average over a macroscopic number of spins with different geometrical locations and nuclear isotopes. Here, we use a scanning tunneling microscope (STM) combined with electron spin resonance (ESR) to measure hyperfine spectra of hydrogenated-Ti on MgO/Ag(100) at low-symmetry binding sites and thereby determine the isotropic and anisotropic hyperfine interactions at the single-atom level. Combining vector-field ESR spectroscopy with STM-based atom manipulation, we characterize the full hyperfine tensors of 47Ti and 49Ti and identify significant spatial anisotropy of the hyperfine interactions for both isotopes. Density functional theory calculations reveal that the large hyperfine anisotropy arises from highly anisotropic distributions of the ground-state electron spin density. Our work highlights the power of ESR-STM-enabled single-atom hyperfine spectroscopy in revealing electronic ground states and atomic-scale chemical environments.