Spectral Functions of Isolated Ce Adatoms on Paramagnetic Surfaces

We report photoemission experiments revealing the full valence electron spectral function of Ce adatoms on Ag(111), W(110), and Rh(111) surfaces. A transfer of Ce $4f$ spectral weight from the ionization peak towards the Fermi level is demonstrated upon changing the substrate from Ag(111) to Rh(111). In the intermediate case of Ce on W(110) the ionization peak is found to be split. This evolution of the spectra is explained by means of first-principles theory, which clearly demonstrates that a reliable understanding of magnetic adatoms on metal surfaces requires simultaneous low and high energy spectroscopic information.

Figure 1

Valence photoelectron energy distribution curves for the clean Ag(111), W(110), and Rh(111) surfaces (a) and in the presence of 0.005 ML, 0.0075 ML, and 0.003 ML of Ce, respectively. These coverages correspond to statistically distributed isolated atoms (b). The curves (c) are the differences between the spectra (b) and (a). All energies $E$ are given relative to the Fermi level $E_F$.

Figure 2

(a) Calculated Ce 4 $f$-electron hybridization functions for isolated adatoms on Ag(111) (red), W(110) (green), and Rh(111) (blue). The real parts are shown as dashed and the imaginary parts as solid lines. (b–d) Calculated $4f$ spectra for single Ce atoms on Ag(111) (b), W(110) (c), and Rh(111) (d) surfaces. The dependence of the spectra on the on-site energies ${ϵ}_f$ is illustrated by showing spectra obtained with different ${ϵ}_f$. All curves are labeled by the corresponding ${ϵ}_f$.

Figure 3

Comparison of experimental (a) and theoretical spectra (b). The theoretical spectra present best fits to the experiment obtained with ${ϵ}_f=-3\mathrm{eV}$, $-1.7\mathrm{eV}$, and $-3.7\mathrm{eV}$ for Ce on Ag(111), W(110), and Rh(111), respectively.

Figure 4

$d$-electron LDOS of substrate atoms which are neighbors of Ce and the Ce $4f$ hybridization functions. For W(110) (b) and Rh(111) (c) the Ce hybridization function follows the shape of the $d$-electron LDOS of the neighboring atoms—in contrast to Ce on Ag(111) (a).