149 research outputs found
Comparison of the effects of puroindoline genotypes on grain and flour properties using near isogenic lines
Strong valence fluctuation in the quantum critical heavy fermion superconductor beta-YbAlB4: A hard x-ray photoemission study
Electronic structures of the quantum critical superconductor beta-YbAlB4 and
its polymorph alpha-YbAlB4 are investigated by using bulk-sensitive hard x-ray
photoemission spectroscopy. From the Yb 3d core level spectra, the values of
the Yb valence are estimated to be ~2.73 and ~2.75 for alpha- and beta-YbAlB4,
respectively, thus providing clear evidence for valence fluctuations. The
valence band spectra of these compounds also show Yb2+ peaks at the Fermi
level. These observations establish an unambiguous case of a strong mixed
valence at quantum criticality for the first time among heavy fermion systems,
calling for a novel scheme for a quantum critical model beyond the conventional
Doniach picture in beta-YbAlB4.Comment: 4 pages, 3 figures, revised version accepted for publication in PR
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
Photoemission evidence for a Mott-Hubbard metal-insulator transition in VO
The temperature () dependent metal-insulator transition (MIT) in VO is
investigated using bulk sensitive hard x-ray ( 8 keV) valence band, core
level, and V 2 resonant photoemission spectroscopy (PES). The valence
band and core level spectra are compared with full-multiplet cluster model
calculations including a coherent screening channel. Across the MIT, V 3
spectral weight transfer from the coherent ( final)
states at Fermi level to the incoherent ( final)
states, corresponding to the lower Hubbard band, lead to gap-formation. The
spectral shape changes in V 1 and V 2 core levels as well as the valence
band are nicely reproduced from a cluster model calculations, providing
electronic structure parameters. Resonant-PES finds that the
states resonate across the V 2 threshold in
addition to the and states. The results support
a Mott-Hubbard transition picture for the first order MIT in VO.Comment: 6 pages, 3 figures. to be published in Phys. Rev.
Revisiting the valence-band and core-level photoemission spectra of NiO
We have re-examined the valence-band (VB) and core-level electronic structure
of NiO by means of hard and soft x-ray photoemission spectroscopy (PES). The
spectral weight of the lowest energy state found to be enhanced in the bulk
sensitive Ni 2p core-level PES. A configuration-interaction model including the
bound state screening has shown significant agreement with the core-level
spectra, and the off and on-resonance VB spectra. These results identify the
lowest energy state in core-level and VB-PES as the Zhang-Rice doublet bound
state, consistent with the spin-fermion model and recent ab initio calculation
with dynamical mean-field theory (LDA + DMFT).Comment: 4 pages, 3 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
- …