Indirect adsorbate-adsorbate interactions mediated by quasi-one-dimensional surface electronic states

We have studied the screening properties of quasi-one-dimensional electronic states which may arise in the troughs of reconstructed (110) surfaces of some fcc metals (Ni and Cu) as chain states localized in the direction perpendicular to the troughs. Motivated by the analysis of the experimental data on the H/Ni(110) system, we discuss the indirect interaction between two H adatoms which is mediated by such states. Using first a linear model of screening of impurity potentials we show that such interaction should exhibit long range oscillations which scale as d⁻¹ for large distances d between the adatoms. By fitting this result to the experimental data available for the H/Ni(110) system we found that a relatively large shift η_a was required to describe these oscillations. This has lead us to use a nonlinear model for the screening of adatoms, based on the Anderson Hamiltonian of impurity screening. This approach yields an indirect interaction between two adatoms which is regular for all d and behaves asymptotically as ˜ cos[2k_Fd − 2η_a(εF)/d where k_F is the Fermi wavevector at the metal surface. The physical significance of the parameters of the model derived thereof can be interpreted in the context of incomplete screening of H adatoms by quasi-one-dimensional electronic chain states existing on the substrate surface.