Character of valence-band states in the Kondo surface alloys CeAg${}_x$/Ag(111) and CePt${}_5$/Pt(111)

The crystal and electronic structures of the CePt${}_5$ and CeAg${}_x$ surface alloys have been investigated by means of low-energy electron diffraction and angle-resolved photoelectron spectroscopy. From measurements performed near the $4d$-$4f$ absorption edge we were able to infer the weight of the $4f$-electron spectral function with respect to the single-particle density of states. While the typical Kondo features at the Fermi energy (Kondo resonance and spin-orbit partner) in the CePt${}_5$ surface alloy were observed, only the $f^0$ ionization structure and the spin-orbit partner were present in the CeAg${}_x$ case. From our experiments, and by comparison to model calculations, we were able to estimate the Kondo temperature in the two systems and investigate parameters contributing to the hybridization strength.

Figure 1

LEED images of the different cerium alloys at 70 eV kinetic energy of the incident electrons: (a) $1\times 1$ reconstruction of clean Pt(111), (b) $2\times 2$ reconstruction of 0.5 ML CePt${}_5$/Pt(111), (c) $(2\times 2)R{30}^{\circ }$ reconstruction of 2 ML CePt${}_5$/Pt(111), (d) $1\times 1$ reconstruction of clean Ag(111), and (e) $(2\times 2)R{30}^{\circ }$ reconstruction of 2 ML CeAg${}_x$/Ag(111).

Figure 2

(a) Momentum integrated off-resonance (blue) and on-resonance (red) experimental ARPES data for CeAg${}_x$ measured along $\overline{\Gamma }\overline{M}$ with $p$ polarization, the green curve shows the difference between the data at on and off resonance that represent the $f$ spectral function. (b) $f$ spectral functions measured along different high-symmetry directions with $s$- and $p$-polarized light, as indicated in the label.

Figure 3

(a) Momentum-integrated spectra for CePt${}_5$ measured with $p$-polarized light along the $\overline{\Gamma }\overline{M}$ direction off (blue) and on resonance (red) and their difference resembling a measure for the 4$f$spectral function (green). (b) Compilation of 4$f$ spectral functions measured along the high-symmetry directions of the surface with $s$- and $p$-polarized light.

Figure 4

ARPES on CeAg${}_x$ surface alloy on the Ag(111) surface along the $\overline{\Gamma }\overline{M}$ direction with $p$-polarized light measured with (a) on-resonant photon energy $h\nu =122$ eV, (b) second derivative thereof, (c) off-resonant photon energy $h\nu =115$ eV, and (d) second derivative thereof. The off-resonant spectrum and its second derivative only show the region within 3 eV below the Fermi energy. The blue and red lines are guides to the eyes for the dispersing and nondispersing bands, respectively.

Figure 5

ARPES on CePt${}_5$ surface alloy on the Pt(111) surface along the $\overline{\Gamma }\overline{M}$ direction with $p$-polarized light measured with (a) on-resonant $h\nu =122$ eV, (c) second derivative thereof, and (b) off-resonant photon energy $h\nu =115$ eV including red and blue bands as guides for the eyes.