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Rev. Sci. Instrum. 96, 033905 (2025).
In angle-resolved photoelectron spectroscopy (ARPES) experiments, the use of polarized light for excitation provides access to the orbital symmetries of the electronic states under investigation. In angle-resolved inverse photoemission (IPE), the equivalent approach is the polarization analysis of the emitted light. So far, this light-polarization analysis has been neglected for intensity reasons due to the much lower cross section of the transitions in IPE compared with ARPES and the lack of suitable polarizers in the vacuum ultraviolet (VUV) spectral range. In this paper, we present the first VUV polarimeter for IPE. A mirror with a polarizing coating of high reflectivity in Brewster-angle geometry is used. An easy-to-use attachment to established photon detectors with high reflectivity and polarization power is presented and tested. We performed IPE measurements of the well-studied L-gap surface state of Cu(111) with separate detection of p- and s-polarized light. The data show strongly enhanced photon intensity for p polarization compared with the intensity for s polarization. Our results are in accordance with the polarization-dependent ARPES measurements of the occupied part of the surface state.

Phys. Rev. B 111, 075117 (2025).
We present an experimental study that offers first insights into the unoccupied electronic states of a pristine ( √ 2 × √ 2 ) ⁢ R ⁢ 4 5 ⁢ ∘ reconstructed Fe₃O₄ (100) surface. We initially demonstrate the successful sample preparation by analyzing the surface periodicity and chemical composition by low-energy electron diffraction and Auger electron spectroscopy, respectively. Using angle-resolved inverse photoemission, we study the unoccupied electronic states. We observe three nondispersive emissions, one dominant feature around 2 e V above the Fermi level and two additional ones at higher energies. For the low-lying triple-split feature, we propose two possible interpretations based on former theoretical studies. We either ascribe it to 3 ⁢ 𝑑 -related bandgroups originating from tetrahedrally and octahedrally coordinated bulk iron atoms or attribute it to a mixture of 3 ⁢ 𝑑 states originating from octahedrally coordinated iron atoms within the bulk and the reconstructed surface layer. The high-lying features are ascribed to bulk bands based on the experimentally observed characteristics.

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.