A theory for the effect of a strong intra-atomic Coulomb repulsion U on the nonadiabatic transfer of charge between a metallic surface and a moving atomic species is presented. Using slave bosons and a nonequilibrium Green's-function technique, we solve the equations appropriate for the U=\ensuremath{\infty} problem in the case when either the atom-surface hopping matrix element is small, or the number of degenerate atomic states is large. We generalize the earlier treatment of Langreth and Nordlander (LN) to include off-diagonal self-energies and present a general numerical scheme for the exact solution of the Dyson equations. We verify that our scheme gives the correct answer in several limiting cases where an exact solution is known, and give quantitative predictions of when deviations from these limits become important. These limits include (1) the simple master equation limit for low velocities and weak coupling, (2) the generalized master equation of LN for larger velocities and atom-surface coupling, (3) the approach to thermal equilibrium when the time dependence is removed, and (4) the maintenance of local thermal equilibrium when the energy parameters vary sufficiently slowly. From a calculation of the instantaneous (nonequilibrium) spectral function of the level on the scattering atom, we are able to study the rate of formation of the Kondo and mixed valent resonances near the Fermi level. We find a slow formation rate for such resonances relative to that of the broader parts of the spectral density centered near the bare atom level positions.
The Kondo effect may be observable in some atom-surface scattering experiments, in particular, those involving alkaline-earth atoms. By combining Keldysh techniques with the noncrossing (NCA) approximation to solve the time-dependent Newns-Anderson Hamiltonian in the $\stackrel{\ensuremath{\rightarrow}}{U}\ensuremath{\infty}$ limit, Shao, Nordlander, and Langreth found an anomalously strong surface-temperature dependence of the outgoing charge state fractions. Here we employ a dynamical
1/N expansion with a finite Coulomb interaction
U to give a more realistic description of the scattering process. We test the accuracy of the
1/N expansion in the
N=1 case of spinless fermions against the exact independent particle solution. We then compare results obtained in the $\stackrel{\ensuremath{\rightarrow}}{U}\ensuremath{\infty}$ limit with the NCA at
N=4 and recover qualitative features already found. Finally, we analyze the realistic situation of Ca atoms with
U=5.8 eV scattered off Cu(001) surfaces. Although the presence of the doubly ionized
Ca2+ species can change the absolute scattered
Ca+ yields, the temperature dependence is qualitatively the same as that found in the $\stackrel{\ensuremath{\rightarrow}}{U}\ensuremath{\infty}$ limit. One of the main difficulties that experimentalists face in attempting 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.
We solve for the electronic Raman scattering response functions on an infinite-dimensional hypercubic lattice employing dynamical mean-field theory. This contribution extends previous work on the nonresonant response to include the mixed and resonant contributions. We focus our attention on the infinite-dimensional spinless Falicov-Kimball model, where the problem can be solved exactly, and the system can be tuned to go through a Mott-Hubbard-like metal-insulator transition. Resonant effects vary in different scattering geometries, corresponding to the symmetries of the charge excitations scattered by the light. We do find that the Raman response is large near the double resonance, where the transfered frequency is close to the incident photon frequency. We also find a joint resonance of both the charge-transfer peak and the low-energy peak when the incident photon frequency is on the order of the interaction strength. In general, the resonance effects can create order of magnitude (or more) enhancements of features in the nonresonant response, especially when the incident photon frequency is somewhat larger than the frequency of the nonresonant feature. Finally, we find that the resonant effects also exhibit isosbestic behavior, even in the
A1g and
B2g sectors, and it is most prominent when the incident photon frequency is on the order of the interaction energy.
Using the fluctuation exchange approximation of the one-band Hubbard model, we discuss the origin of the changing Fermi surface volume in underdoped cuprate systems due to the transfer of occupied states from the Fermi surface to its shadow, resulting from strong dynamical antiferromagnetic short-range correlations. The momentum and temperature dependence of the quasiparticle scattering rate shows unusual deviations from the conventional Fermi-liquid-like behavior. Their consequences for the changing Fermi surface volume are discussed. Here, we investigate in detail which scattering processes might be responsible for a violation of the Luttinger theorem. Finally, we discuss the formation of hole pockets near half filling. \textcopyright{} 1996 The American Physical Society.