K. Makoshi

Singlet-triplet conversion of He∗(1s2s) by metal surfaces

Abstract The singlet-triplet conversion of the excited He(1s2s) metastable atom, approaching the metal surface with relatively low work function, is delt with on the basis of an extended Newns-Anderson model allowing the atom to have spin singlet and triplet states. After a canonical transformation, we show that a virtual process through the ionic states, of both the positive and the negative ions, makes the conversion possible. The numerical results show that in a certain range of parameters, the conversion possibly takes place in a region rather far from the surface.

Interpolation formula for the Auger neutralization probability

Abstract The higher order perturbation terms of the Auger neutralization process are examined with use of the Keldysh Green function method. An explicit condition is found to guarantee the Hagstrum equation. With the aid of numerical analyses, an interpolation formula is proposed for the Auger neutralization of an ion with an arbitrary velocity.

Ionization of metastable He(1s2s) atoms by alkalated surfaces

Abstract We calculate the ionization probability for singlet and triplet metastable He(1s2s) atoms scattered from potassium covered surfaces, on the basis of the resonant tunnelling process. We do not assume the trajectory approximation, but we do assume classical motion on the potential energy curves, with crossing between neutral and ionic curves at a given point calculated from electronic tunnelling probabilities. Energy spectra of the He + ions are also calculated. The results are found to be somewhat sensitive to tunnelling probability as a function of distance from the surface. Results are compared with experimental ionization probabilities measured by Roussel. The agreement is found to be fair if the tunneling rate is parameterized according to the theory of Janev et al. A simple interpretation is given.

Effect of atom motion on metastable deexcitation spectroscopy

The effect of atom motion on the metastable deexcitation spectrum is considered. The time-dependence of the Auger deexcitation matrix elements is explicitly considered in the Keldysh Green-function formalism. In the slow-motion limit, the life-time effect is shown to renormalize the Auger matrix elements as the quasi-static approach speculates. Also considered is the effect on the anomalous Fermi surface effect, previously pointed out to be expected in the metastable de-excitation spectroscopy at metal surfaces — beam Kondo effect. The effect is shown to result in the broadening of the threshold singularity, which is observed in the transition rate, similar to the surface-temperature effect.

Beam Kondo effect? — Possible anomalous penning deexcitation spectrum

Abstract It is shown that the Penning deexcitation spectrum of the triplet 2s excited helium atom beam at metal surfaces can have a threshold anomaly, which is the Kondo effect. The time-dependent Newns-Anderson model is used to analyze the transition rate of the deexcitation in the quasi-static approximation. The effect is due to the spin as well as potential scattering of conduction electrons by the He atom in the triplet excited state as the initial state interaction. Line shape of the Penning deexcitation spectrum is discussed, and clean surfaces of alkali metals are pointed out to be possible candidates to observe this many body effect.

Parallel energy dependence of Auger neutralisation probability

The parallel energy dependence of the Auger neutralisation probability in the ion beam scattering on a metal surface is studied. The Auger matrix element with some simple models that reflect the lattice periodicity is calculated. It is examined both analytically and numerically how the survival probability of ions should behave as a function of the ion beam energy and the angle of incidence. The results show qualitatively good agreement with the experiments.

Second order selfenergy and rate equation in time-dependent Auger processes

The Keldysh Green function formalism is employed to examine the validity of the rate equation description for time-dependent Auger type processes taking place in the ion- or metastable atom-surface collision such as Auger neutralization and metastable deexcitation. The second order selfenergy is considered in the Dyson equation, and the condition is expressed when the time-ordering operation is lifted

Exact calculation for the time-dependent Newns-Anderson model in a small system: II. Scattering geometry

Abstract The charge transfer problem between metal surfaces and moving atoms is investigated in the time-dependent Newns-Anderson model. Exact numerical calculations are performed for a small system with 8 electrons in the scattering geometry of positive ion incidence. The intra-atomic Coulomb interaction is treated without approximations. The results are compared with those of the Hartree-Fock approximation. From the comparison, we see that the Hartree-Fock approximation provides rather good results for scattering to non-negative charge states, but for the fraction of negative ions, the electron correlation effect on the atom seems essential.

Exact calculation for the time-dependent newns-Anderson model in a small system

Abstract The charge transfer problem between metal surfaces and moving atoms is investigated in the time-dependent Newns-Anderson model. Exact calculations are performed for a small system with 8 electrons. The intra-atomic Coulomb interaction is treated without approximations. The results are compared with those of the Hartree-Fock approximation. From the comparison, we see that the Hartree-Fock approximation provides rather good results for the atom-velocity dependence except for its prefactor, but for the fraction of negative ion, the electron correlation effect on the atom seems essential.

Uniform susceptibility of nearly ferromagnetic antiferromagnet

Abstract The temperature dependence of the uniform susceptibility near the Neel temperature in the paramagnetic region is discussed in the context of the self-consistent renormalization theory for weakly ferro- and antiferromagnetic metals. The self-consistent equations for the uniform susceptibility and the staggered susceptibility are solved simultaneously with the assumption that both of the ferromagnetism and the antiferromagnetism are close to the instability. It is found that the sign of the temperature derivative of the uniform susceptibility near the Neel point is determined by the relation between the coupling constants among spin fluctuation modes, similar to the condition of the coexistence of the two ordering modes with symmetry breaking.