415 research outputs found
Modelling the Localized to Itinerant Electronic Transition in the Heavy Fermion System CeIrIn5
We address the fundamental question of crossover from localized to itinerant
state of a paradigmatic heavy fermionmaterial CeIrIn5. The temperature
evolution of the one electron spectra and the optical conductivity is predicted
from first principles calculation. The buildup of coherence in the form of a
dispersive many body feature is followed in detail and its effects on the
conduction electrons and optical conductivity of the material is revealed. We
find multiple hybridization gaps and link them to the crystal structure of the
material. Our theoretical approach explains the multiple peak structures
observed in optical experiments and the sensitivity of CeIrIn5 to substitutions
of the transition metal element and may provide a microscopic basis for the
more phenomenological descriptions currently used to interpret experiments in
heavy fermion systems.Comment: 12 pages, 3 figure
Electronic structures of CeRu ( = Si, Ge) in the paramagnetic phase studied by soft X-ray ARPES and hard X-ray photoelectron spectroscopy
Soft and hard X-ray photoelectron spectroscopy (PES) has been performed for
one of the heavy fermion system CeRuSi and a -localized ferromagnet
CeRuGe in the paramagnetic phase. The three-dimensional band structures
and Fermi surface (FS) shapes of CeRuSi have been determined by soft
X-ray -dependent angle resolved photoelectron spectroscopy (ARPES). The
differences in the Fermi surface topology and the non- electronic
structures between CeRuSi and CeRuGe are qualitatively
explained by the band-structure calculation for both itinerant and
localized models, respectively. The Ce valences in CeRu ( = Si, Ge)
at 20 K are quantitatively estimated by the single impurity Anderson model
calculation, where the Ce 3d hard X-ray core-level PES and Ce 3d X-ray
absorption spectra have shown stronger hybridization and signature for the
partial contribution to the conduction electrons in CeRuSi.Comment: 8figure
Direct experimental verification of applicability of single-site model for angle integrated photoemission of small concentrated Ce compounds
Bulk-sensitive high-resolution Ce 4f spectra have been obtained from 3d
4f resonance photoemission measurements on LaCeAl and
LaCeRu for . The 4f spectra of
low-Kondo-temperature () (La,Ce)Al are essentially identical except
for a slight increase of the Kondo peak with , which is consistent with a
known increase of with . In contrast, the 4f spectra of high-
(La,Ce)Ru show a Kondo-like peak and also a 0.5 eV structure which
increases strongly with . The resonance photon-energy dependences of the two
contributions are different and the origin of the 0.5 eV structure is still
uncertain.Comment: submitted to SCES 2001, two-columnn format, modified tex
Electron correlation in FeSe superconductor studied by bulk-sensitive photoemission spectroscopy
We have investigated the electronic structures of recently discovered
superconductor FeSe by soft-x-ray and hard-x-ray photoemission spectroscopy
with high bulk sensitivity. The large Fe 3d spectral weight is located in the
vicinity of the Fermi level (EF), which is demonstrated to be a coherent
quasi-particle peak. Compared with the results of the band structure
calculation with local-density approximation, Fe 3d band narrowing and the
energy shift of the band toward EF are found, suggesting an importance of the
electron correlation effect in FeSe. The self energy correction provides the
larger mass enhancement value (Z^-1=3.6) than in Fe-As superconductors and
enables us to separate a incoherent part from the spectrum. These features are
quite consistent with the results of recent dynamical mean-field calculations,
in which the incoherent part is attributed to the lower Hubbard band.Comment: 8 pages, 5 figures, 1 talbl
Filling of the Mott-Hubbard gap in the high temperature photoemission spectrum of (V_0.972Cr_0.028)_2O_3
Photoemission spectra of the paramagnetic insulating (PI) phase of
(V_0.972Cr_0.028)_2O_3, taken in ultra high vacuum up to the unusually high
temperature (T) of 800 K, reveal a property unique to the Mott-Hubbard (MH)
insulator and not observed previously. With increasing T the MH gap is filled
by spectral weight transfer, in qualitative agreement with high-T theoretical
calculations combining dynamical mean field theory and band theory in the local
density approximation.Comment: 4 pages, 4 figure
- …