Borisov, A. G., Sametoglu, V., Winkelmann, A., Kubo, A., Pontius, N., Zhao, J., Silkin, V. M., Gauyacq, J. P., Chulkov, E. V., Echenique, P. M., Petek, H.
π Resonance of chemisorbed alkali atoms on noble metals
Physical Review Letters 101, (26),pp 266801/1-4 (2008)
We have performed a joint experimental and theoretical study of the unoccupied electronic structure of alkali adsorbates on the (111) surfaces of Cu and Ag. Combining angle- and time-resolved two-photon photoemission spectroscopy with wave packet propagation calculations we show that, along with the well known σ resonance oriented along the surface normal, there exist long-lived alkali-localized resonances oriented parallel to the surface (π symmetry). These new resonances are stabilized by the projected band gap of the substrate and emerge primarily from the mixing of the p and d Rydberg orbitals of the free alkali atom modified by the interaction with the surface.