Evidence of Coexisting Kondo Screening and Valence Fluctuations in the CePd 7 /pd(001) Surface Alloy

We report on the electronic structure of a clean, well ordered CePd7 surface alloy that was grown in a unique (root 5 x root 5)R26.6 degrees structure, as evidenced by low-energy electron diffraction and Auger electron spectroscopy. Resonant photoemission measurements at the 4d -> 4f absorption edge evidenced strong Ce 4f derived states having two components near the Fermi level. This observation can be explained by considering very different hybridizations between Ce 4f and the Pd 4d electrons in the surface and deeper layers. In the former, the hybridization is weak and leads to a spin-dependent screening with low Kondo temperature, while in the latter the hybridization recovers the value of bulk alloy and thus leads to strong charge fluctuations.