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Among the lanthanides, Yb and Ce are of fundamental interest, because of a strong interaction between 4f and valence-band (VB) states leading to mixed-valence and Kondo phenomena in a number of compounds. This analogy between Yb and Ce systems has been explained on the basis of the electron-hole symmetry of the quasiatomic 4f shell. While the correspondence has been established for a number of compounds, no evidence for such a symmetry has been reported up to now for the pure metals. Motivated by the recent work [1] where observed k-dependent splitting of the 4f ionization peak of Ce/W(110) were correctly described in the framework of the simplified periodic Anderson model, in the present contribution we report on the results of the angle-resolved photoelectron studies of thin layers of Yb (1-3 ML-thick) on W(110) surface. The clear splitting of the Yb 4f7/2 state was observed in the PE spectra measured around point. The measured PE spectra were analyzed by means of the simplified periodic Anderson model (PAM) that has been recently successfully applied for interpretation of angle-resolved PE data. In this model the influence of substrate W 5d electron states to the 4f-VB hybridization matrix elements can not be unambiguously estimated from the band-structure calculations due to incommensurate Yb and W surfaces. In this case, taking into account that escaping electrons are analyzed for the emission direction close to the surface normal, we may expect that the PE intensities measured for a pure W(110) surface are determined mainly by W 5d orbitals directed out-of-surface. Then, it could be assumed that namely these orbitals are responsible for 4f-VB hybridization, and the respective PE intensities could be chosen as a measure for the VB contribution to the hybridization matrix element.
[1] D. V. Vyalikh et al., Phys. Rev. Lett. 96, 026404 (2006). |