390 research outputs found
Electronic correlations and Hund's coupling effects in SrMoO revealed by photoemission spectroscopy
We investigate the electronic structure of a perovskite-type Pauli paramagnet
SrMoO3 (t2g2) thin film using hard x-ray photoemission spectroscopy and compare
the results to the realistic calculations that combine the density functional
theory within the local-density approximation (LDA) with the dynamical-mean
field theory (DMFT). Despite the clear signature of electron correlations in
the electronic specific heat, the narrowing of the quasiparticle bands is not
observed in the photoemission spectrum. This is explained in terms of the
characteristic effect of Hund's rule coupling for partially-filled t2g bands,
which induces strong quasiparticle renormalization already for values of
Hubbard interaction which are smaller than the bandwidth. The interpretation is
supported by additional model DMFT calculations including Hund's rule coupling,
that show renormalization of low-energy quasiparticles without affecting the
overall bandwidth. The photoemission spectra show additional spectral weight
around -2 eV that is not present in the LDA+DMFT. We interpret this weight as a
plasmon satellite, which is supported by measured Mo, Sr and Oxygen core-hole
spectra that all show satellites at this energy.Comment: 8 pages, 7 figure
Evidence for suppressed metallicity on the surface of La2-xSrxCuO4 and Nd2-xCexCuO4
Hard X-ray Photoemission spectroscopy (PES) of copper core electronic states,
with a probing depth of 60 \AA, is used to show that the Zhang-Rice
singlet feature is present in LaCuO but is absent in NdCuO.
Hole- and electron doping in LaSrCuO (LSCO) and
NdCeCuO (NCCO) result in new well-screened features which are
missing in soft X-ray PES. Impurity Anderson model calculations establish
metallic screening as its origin, which is strongly suppressed within 15
of the surface. Complemented with X-ray absorption spectroscopy,
the small chemical-potential shift in core levels ( eV) are shown to
be consistent with modifications of valence and conduction band states spanning
the band gap ( eV) upon hole- and electron-doping in LSCO and NCCO.Comment: 4 pages, 4 figure
High energy, high resolution photoelectron spectroscopy of Co2Mn(1-x)Fe(x)Si
This work reports on high resolution photoelectron spectroscopy for the
valence band of Co2Mn(1-x)Fe(x)Si (x=0,0.5,1) excited by photons of about 8 keV
energy. The measurements show a good agreement to calculations of the
electronic structure using the LDA+U scheme. It is shown that the high energy
spectra reveal the bulk electronic structure better compared to low energy XPS
spectra. The high resolution measurements of the valence band close to the
Fermi energy indicate the existence of the gap in the minority states for all
three alloys.Comment: 14 pages, 5 figures, submitted to J. Phys. D: Appl. Phy
Recoil effects of photoelectrons in a solid
High energy resolution C 1 photoelectron spectra of graphite were measured
at the excitation energy of 340, 870, 5950 and 7940eV using synchrotron
radiation. On increasing the excitation energy, i.e., increasing kinetic energy
of the photoelectron, the bulk origin C 1 peak position shifts to higher
binding energies. This systematic shift is due to the kinetic energy loss of
the high-energy photoelectron by kicking the atom, and is clear evidence of the
recoil effect in photoelectron emission. It is also observed that the
asymmetric broadening increases for the higher energy photoelectrons. All these
recoil effects can be quantified in the same manner as the M\"ossbauer effect
for -ray emission from nuclei embedded in crystals.Comment: 4 pages, 2 figure
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