Many-body effects in the electron spectroscopies of incompletely filled bands (original) (raw)
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Phys. Rev. B 87, 165136 (2013), 2013
We propose a variational method to calculate the two-hole propagators relevant for Auger spectroscopy in transition-metal oxides. This method can be thought of as an intermediary step between the full solution (which is difficult to generalize to systems with partially filled bands) and the impurity approximation. Like the former, our solution has full translational invariance, and like the latter, it can be generalized to certain types of systems with partially filled bands. Here we compare both our variational approximation and the impurity approximation against the exact solution for a simple one-dimensional model with filled bands. We show that when the energies of the eigenstates residing primarily on the transition-metal ions do not overlap with those of the eigenstates residing primarily on oxygen ions, both approximations are valid but the variational approach is superior.
Journal of Physics: Conference Series, 2008
We propose the foundations of an extended Auger Line Shape Analysis aiming to include the Coster-Kronig (CK) satellites in solid state spectra. In many solids like Cu and Zn metals they show up as intense high binding energy satellites of the Core-Valence-Valence (CVV) lines. Our theory covers the whole range between weak and strong correlation. We find that the satellites display three-hole and distorted two-hole features along with uncorrelated band-like continua.
Variational approach for calculating Auger electron spectra: Going beyond the impurity approximation
Physical Review B, 2013
We propose a novel variational method to calculate the two-hole propagators relevant for Auger spectroscopy in transition metal oxides. This method can be thought of as an intermediary step between the full solution (which is difficult to generalize to systems with partially filled bands) and the impurity approximation. Like the former, our solution has full translational invariance, and like the latter, it can be generalized to certain types of systems with partially filled bands. Here we compare both our variational approximation and the impurity approximation against the exact solution for a simple one-dimensional model with filled bands. We show that when the energies of the eigenstates residing primarily on the transition metal ions do not overlap with those of the eigenstates residing primarily on Oxygen ions, both approximations are valid but the variational approach is superior.
The elastic scattering factor in Auger electron spectroscopy
Surface Science, 1983
We have calculated the contribution of elastic scattering of primary electrons to the Auger yield for Al, Si and Cu. We found an important contribution of the forward scattered electrons. We have also measured the primary energy dependence of the Auger yield for pure Al. Si and Cu. We found differences among calculations and measurements as great as 40%. which are attributed to uncertainties in escape depth and Auger transition rates rather than to the scattering effect.
Role of Off-site Interactions in Auger Lineshape Analysis from Closed Bands Systems
Physica Scripta, 1992
The Cini-Sawatzky theory of Auger CVV line shapes from solids and its extensions are based on single or multi-band Hubbard or Anderson models, retaining only the intra-atomic repulsion terms. In this work, we study the role of off-site interactions in closed bands systems. The local interaction terms are treated exactly, as usual, while off-site correlations are introduced as a self-energy-like correction, on perturbative grounds. Our main results is that the effect of off-site interactions must be taken into account to obtain simultaneous agreement for the shape and the energy position of the C V V spectra. This conclusion is supported by recent experimental evidence and affects the derivation of U values from line shape analysis.
Physical Review Letters, 1998
We calculate Auger spectra given by the two-hole Green's function from orbitally degenerate Hubbard-like models as a function of correlation strength and band filling. The resulting spectra are qualitatively different from those obtained from fully-filled singly degenerate models due to the presence of screening dynamics and multielectron excitations. Application to a real system shows remarkable agreement with experimental results leading to reinterpretation of spectral features.
Journal of Electron Spectroscopy and Related Phenomena, 1997
The Ar L 2,3 -MM Auger spectrum induced by impact of 2.0 keV electrons was measured with high resolution (68 Ϯ 4 meV) in the 15-90Њ angular region. Relative yields, level widths and transition energies have been determined for the diagram Auger lines originating from the 2 P 1=2 and 2 P 3=2 initial vacancy states. The data are compared with those of earlier experimental studies and theoretical calculations, including multiconfiguration Hartree-Fock calculations performed in this work. The isotropy of the studied lines has been confirmed. The measured relative intensities of the fine-structure components of the L 23 -MM ( 3 P 0, 1, 2 ) Auger triplets have been found different from those obtained in theoretical calculations and earlier experiments. ᭧ 1997 Elsevier Science B.V.
Auger photoelectron coincidence spectroscopy (APECS), in which the Auger spectra are measured in coincidence with the core level photoelectron, is capable of pulling difficult to observe low energy Auger peaks out of a large background due mostly to inelastically scattered valence band (VB) photoelectrons. However the APECS method alone cannot eliminate the background due to valence band photoemission processes in which the initial photon energy is shared by two or more electrons and one of the electrons is in the energy range of the core level photoemission peak. Here we describe an experimental method to determine the contributions from these background processes and apply this method in the case of copper M 3 VV Auger spectrum obtained in coincidence with the 3p 3/2 photoemission peak. A beam of 200 eV photons was incident on a Cu(1 0 0) sample and a series of coincidence measurements were performed using a spectrometer equipped with two cylindrical mirror analyzers (CMAs). One CMA was set at series of fixed energies that ranged between the energy of the core and the VB peaks. The other CMA was scanned over a range corresponding to electrons leaving the surface between 0 eV and 70 eV. The set of measured spectra were then fit to a parameterized function which was extrapolated to determine the background in the APECS spectra due to multi-electron and inelastic VB photoemission processes. The extrapolated background was subtracted from the APECS spectrum to obtain the spectrum of electrons emitted solely as the result of the Auger process. A comparison of the coincidence spectrum with the same spectrum with background removed shows that in the case of Cu M 3 VV the background due to the inelastic scattering of VB electrons is negligible in the region of the Auger peak but is more than half the total signal down in the low energy tail of the Auger peak.