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Phys. Rev. Research 6, 023314 (2024).
Pt(111) hosts a surface resonance with peculiar properties concerning energy vs momentum dispersion and spin texture. At variance with the free-electron-like behavior of the 𝐿 -gap Shockley-type surface states on the fcc(111) surfaces of Au, Ag, and Cu, it splits into several branches with distinct spin polarization around the center of the surface Brillouin zone Γ . Theoretical predictions based on density-functional theory vary depending on the particular functionals used. To clarify this issue, we investigate the atomic structure of Pt(111) by low-energy electron diffraction and the unoccupied electronic structure by spin- and angle-resolved inverse photoemission. The experimental results are backed by theoretical studies using different functionals, which show that the characteristics of the surface band depend critically on the lattice constant. From the analysis of the energy-dependent low-energy electron diffraction intensities, we derive structural parameters of the Pt(111) surface relaxation with high accuracy. In addition, we give an unambiguous definition of the nonequivalent mirror-plane directions ΓM and ΓM' at fcc(111) surfaces, which is consistent with band-structure calculations and inverse-photoemission data. Concerning the surface resonance at the bottom of the 𝐿 gap, we identified a delicate interplay of several contributions. Lattice constant, hybridization with 𝑑 bands, and the influence of spin-orbit interaction are critical ingredients for understanding the peculiar energy dispersion and spin character of the unoccupied surface resonance.

Phys. Rev. B 109, 165417 (2024).
We present a study of the unoccupied electronic states of one monolayer (ML) Tl epitaxially grown on Ag(111) in a moiré superstructure. This two-dimensional atomic-layer material is investigated by scanning tunneling microscopy/spectroscopy, spin-resolved inverse photoemission, and calculations based on density functional theory. The unoccupied band structure exhibits characteristic spin-dependent hybridization between overlayer states influenced by the substrate. Most of the experimentally observed bands, their E(k_II) behavior, and their Rashba-type spin dependence can be qualitatively described by a simple model for a Tl/Ag bilayer. A more realistic superstructure model reflecting the moiré structure provides deeper insight into the hybridization mechanisms for states of different orbital composition, further elucidated by calculations of the charge densities. Experimentally, E(k_II)measurements as well as the analysis of spin-dependent spectral intensities allow us to distinguish different orbital contributions in the respective spin-up and spin-down components leading to hybridization gaps with spin-dependent size. Most interestingly, spin-dependent hybridization with overlayer states was discovered for an image-potential-induced surface band, which is mainly located in front of the sample surface.

New J.Phys. 25 (2023) 103037.
In a combined experimental and theoretical study, we investigate the interplay of spin–orbit
interaction (SOI) and exchange interaction (XI) in the electronic structure of ultrathin Ni films on
W(110). Using spin- and angle-resolved inverse photoemission, we observe that the size of the spin
splitting of Ni-related exchange-split states differs for opposite magnetization directions. A
quenched spin splitting for one of the magnetization directions reveals a contribution of SOI on an
equal footing with XI. Using density-functional theory calculations, we explore the underlying
mechanisms responsible for the experimentally observed coupling of SOI and XI. We find that a
hybridization between adsorbate and substrate states, along with a high probability density of the
respective states at the heavy W nuclei, cause the strong influence of SOI on the Ni-related
exchange-split states.