Anisotropic hyperfine interaction of surface-adsorbed single atoms

Abstract

Hyperfine interactions between electron and nuclear spins have been widely used in material science, organic chemistry, and structural biology as a sensitive probe to the local chemical environment through spatial identification of nuclear spins. With the nuclear spins identified, the isotropic and anisotropic components of the hyperfine interactions in turn offer unique insight into the electronic ground-state properties 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. Here, we use a scanning tunneling microscope (STM) combined with electron spin resonance (ESR) to measure hyperfine spectra of hydrogenated-titanium (Ti) atoms on MgO/Ag(100) and thereby determine the isotropic and anisotropic hyperfine interactions at the single-atom level. By combining vector-field ESR spectroscopy with STM-based atom manipulation, we characterize the full hyperfine tensor of individual Ti-47 and Ti-49 atoms and identify significant spatial anisotropy of hyperfine interaction for both isotopes when they are adsorbed at low-symmetry binding sites. Density functional theory calculations reveal that the large hyperfine anisotropy arises from a highly anisotropic distribution of the ground-state electron spin density. Our 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 nano-electronvolt resolution.

17 pages, 4 figures

References in corpus (4)

• Quantum ESPRESSO toward the exascale
• Engineering the eigenstates of coupled spin-1/2 atoms on a surface
• Harnessing the Quantum Behavior of Spins on Surfaces
• Experimental Determination of a Single Atom Ground State Orbital through Hyperfine Anisotropy

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• Spin-State Engineering of Single Titanium Adsorbates on Ultrathin Magnesium Oxide
• Coherent and Dissipative Spin Torques in Quantum Dots: A Unified Framework for Quantum Spin Dynamics
• 3d-oxide molecules to tailor large magnetic anisotropy energies on MgO films
• Theory of Electron Spin Resonance Scanning Tunneling Microscopy: The First Decade