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Spin-dependent hybridization of image-potential states and overlayer states: One monolayer of Tl on Ag(111)

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(kII) 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(kII)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.

Interplay of spin–orbit and exchange interaction in a ferromagnet/heavy-metal hybrid system: Ni on W(110)

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.

Structural and electronic properties of Tl films on Ag(111): From ( √ 3× √ 3) surface alloy to moiré superstructure

Phys. Rev. B 107, 205144 (2023).
We present a detailed study of the growth behavior and the electronic properties of thin Tl films epitaxially grown on Ag(111). We combine experimental results obtained by Auger electron spectroscopy, low-energy electron diffraction, scanning tunneling microscopy, scanning tunneling spectroscopy (STS), and inverse photoemission (IPE). The electronic properties identified by STS and IPE are substantiated via density functional theory (DFT) calculations. For a Tl coverage of 0.33 atomic layers (AL), our experimental results show the formation of small patches with a (√3 x √3)
reconstruction. With STS and IPE, we observe two dominant empty-state electronic features at EEF1.6 and 3.5 eV, which are attributed to downward dispersing s,pz-derived states and to states with pz orbital symmetry, respectively. On the basis of band structure and charge distribution calculations, we discuss the variation of the binding energies of the respective electronic features observed by STS and IPE. Above 0.5 AL, a moiré superstructure evolves due to the rather large lattice mismatch between the Tl adlayer and Ag(111) which exhibits a sharp spectroscopic feature at around EEF3.1 eV in STS and IPE. The comparison with DFT calculations suggests that it originates from a predominantly pz-like surface state. For even larger film thicknesses up to 4 AL, we find a rotation of the Tl layer with respect to the Ag(111) substrate of α=±(2.50±0.20).

Surface electronic structure of Re(0001): A spin-resolved photoemission study

Phys. Rev. B 107, 165420 (2023).
The surface electronic structure of Re(0001) has been investigated in a combined experimental and theoretical study. Spin- and angle-resolved photoemission was employed to unravel the spin-dependent E(k) dispersion of electronic states along the GM and  GK directions. The results are compared with band-structure calculations based on density-functional theory. Additional calculations include transitions into final states by taking into account the corresponding matrix elements. Recently, Shockley- and Tamm-type surface states close to EF were identified, which were found to be mixed by spin-orbit coupling. Here, we determined the Rashba parameter αR of the surface state around G to 0.32 and 0.34 eVÅ along GM and GK, respectively. Furthermore, we extend our analysis to a wider E(k) range revealing a multitude of electronic states along both high-symmetry directions. In particular, Rashba-type spin splittings are observed around the high-symmetry G and M points. At variance with theoretical predictions for a perfect hcp(0001) surface, we do not find any out-of-plane spin polarization. This is caused by monatomic steps of a real Re(0001) surface with alternating terminations, leading on average to an effective sixfold surface symmetry and vanishing net out-of-plane spin polarization.  

Comment on “Spin- and angle-resolved inverse photoemission setup with spin orientation independent from electron incidence angle” [Rev. Sci. Instrum. 93, 093904 (2022)]

Rev. Sci. Instrum. 94, 037101 (2023).
The paper under discussion promises a spin- and angle-resolved inverse-photoemission (IPE) setup, where the spin-polarization direction of the electron beam used for excitation “can be tuned to any preferred direction” while “preserving the parallel beam condition.” We support the idea to improve IPE setups by introducing a three-dimensional spin-polarization rotator, but we put the presented results to the test by comparing them with the literature results obtained by existing setups. Based on this comparison, we conclude that the presented proof-ofprinciple experiments miss the target in several aspects. Most importantly, the key experiment of tuning the spin-polarization direction under otherwise allegedly identical experimental conditions causes changes in the IPE spectra that are in conflict with existing experimental results and basic quantum-mechanical considerations. We propose experimental test measurements to identify and overcome the shortcomings.