407 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
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
High-resolution Ce 3d-edge resonant photoemission study of CeNi_2
Resonant photoemission (RPES) at the Ce 3d -> 4f threshold has been performed
for alpha-like compound CeNi_2 with extremely high energy resolution (full
width at half maximum < 0.2 eV) to obtain bulk-sensitive 4f spectral weight.
The on-resonance spectrum shows a sharp resolution-limited peak near the Fermi
energy which can be assigned to the tail of the Kondo resonance. However, the
spin-orbit side band around 0.3 eV binding energy corresponding to the f_{7/2}
peak is washed out, in contrast to the RPES spectrum at the Ce 3d -> 4f RPES
threshold. This is interpreted as due to the different surface sensitivity, and
the bulk-sensitive Ce 3d -> 4f RPES spectra are found to be consistent with
other electron spectroscopy and low energy properties for alpha-like
Ce-transition metal compounds, thus resolves controversy on the interpretation
of Ce compound photoemission. The 4f spectral weight over the whole valence
band can also be fitted fairly well with the Gunnarsson-Schoenhammer
calculation of the single impurity Anderson model, although the detailed
features show some dependence on the hybridization band shape and (possibly) Ce
5d emissions.Comment: 4 pages, 3 figur
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
Photoemission study of (VM)O (M=Cr, Ti)
We present high-resolution bulk-sensitive photoemission spectra of
(VM)O (M=Cr, Ti). The measurements were made for the
paramagnetic metal (PM), paramagnetic insulator (PI), and antiferromagnetic
insulator (AFI) phases of (VM)O with the samples of =
0, 0.012, and 0.028 for Cr-doping and = 0.01 for Ti-doping. In the PM
phase, we observe a prominent quasiparticle peak in general agreement with
theory, which combines dynamical mean-field theory with the local density
approximation (LDA+DMFT). The quasiparticle peak shows a significantly larger
peak width and weight than in the theory. For both the PI and AFI phases, the
vanadium 3d parts of the valence spectra are not simple one peak structures.
For the PI phase, there is not yet a good theoretical understanding of these
structures. The size of the electron removal gap increases, and spectral weight
accumulates in the energy range closer to the chemical potential, when the PI
to AFI transition occurs. Spectra taken in the same phases with different
compositions show interesting monotonic changes as the dopant concentration
increases, regardless of the dopant species. With increased Cr-doping, the AFI
phase gap decreases and the PI phase gap increases.Comment: 13 pages, 16 figures. accepted for publication in Physical Review
Photoemission Spectroscopy and the Unusually Robust One Dimensional Physics of Lithium Purple Bronze
Temperature dependent photoemission spectroscopy in Li0.9Mo6O17 contributes
to evidence for one dimensional physics that is unusually robust. Three generic
characteristics of the Luttinger liquid are observed, power law behavior of the
k-integrated spectral function down to temperatures just above the
superconducting transition, k-resolved lineshapes that show holon and spinon
features, and quantum critical (QC) scaling in the lineshapes. Departures of
the lineshapes and the scaling from expectations in the Tomonaga Luttinger
model can be partially described by a phenomenological momentum broadening that
is presented and discussed. The possibility that some form of 1d physics
obtains even down to the superconducting transition temperature is assessed.Comment: submitted to JPCM, Special issue article "Physics in one dimension
Raman and fluorescence contributions to resonant inelastic soft x-ray scattering on LaAlO/SrTiO heterostructures
We present a detailed study of the Ti 3 carriers at the interface of
LaAlO/SrTiO heterostructures by high-resolution resonant inelastic soft
x-ray scattering (RIXS), with special focus on the roles of overlayer thickness
and oxygen vacancies. Our measurements show the existence of interfacial Ti
3 electrons already below the critical thickness for conductivity and an
increase of the total interface charge up to a LaAlO overlayer thickness of
6 unit cells before it levels out. By comparing stoichiometric and oxygen
deficient samples we observe strong Ti 3 charge carrier doping by oxygen
vacancies. The RIXS data combined with photoelectron spectroscopy and transport
measurements indicate the simultaneous presence of localized and itinerant
charge carriers. However, it is demonstrated that the relative amount of
localized and itinerant Ti electrons in the ground state cannot be deduced
from the relative intensities of the Raman and fluorescence peaks in excitation
energy dependent RIXS measurements, in contrast to previous interpretations.
Rather, we attribute the observation of either the Raman or the fluorescence
signal to the spatial extension of the intermediate state reached in the RIXS
excitation process.Comment: 9 pages, 6 figure
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