ROOM-TEMPERATURE KONDO EFFECT IN ATOM-SURFACE SCATTERING - DYNAMICAL 1 N APPROACH/

The Kondo effect may be observable in some atom-surface scattering exp eriments, in particular, those involving alkaline-earth atoms. By comb ining Keldysh techniques with the noncrossing (NCA) approximation to s olve the time-dependent Newns-Anderson Hamiltonian in the U-->infinity limit, Shao, Nordlander, and Langreth found an anomalously strong sur face-temperature dependence of the outgoing charge state fractions. He re we employ a dynamical 1/N expansion with a finite Coulomb interacti on U to give a more realistic description of the scattering process. W e test the accuracy of the 1/N expansion in the N= 1 case of spinless fermions against the exact independent particle solution. We then comp are results obtained in the U-->proportional to limit with the NCA at N=4 and recover qualitative features already found. Finally, we analyz e the realistic situation of Ca atoms with U= 5.8 eV scattered off Cu( 001) surfaces. Although the presence of the doubly ionized Ca2+ specie s can change the absolute scattered Ca+ yields, the temperature depend ence is qualitatively the same as that found in the U-->infinity limit . One of the main difficulties that experimentalists face in attemptin g to detect this effect is that the atomic velocity must be kept small enough to limit kinematic smearing of the Fermi surface of the metal.