128 research outputs found
An angle-resolved soft x-ray spectroscopy study of the electronic states of single crystal MgB2
Angle-resolved soft x-ray measurements made at the boron K-edge in single
crystal MgB2 provide new insights into the B-2p local partial density of both
unoccupied and occupied band states. The strong variation of absorption with
incident angle of exciting x-rays permits the clear separation of contributions
from \sigma states in the boron plane and \pi states normal to the plane. A
careful comparison with theory accurately determines the energy of selected
critical points in the conduction band. Resonant inelastic x-ray emission
at an incident angle of 15 degrees shows a large enhancement of the emission
spectra within about 0.5 eV of the Fermi level that is absent at 45 degrees and
is much reduced at 60 degrees. We conclude that momentum transferred from the
resonant inelastic x-ray scattering (RIXS) process couples empty and filled
states across the Fermi level.Comment: Accepted to PRB. 13 pages, 6 figure
Soft x-ray spectroscopy experiments on the near K-edge of B in MB2 (M=Mg, Al, Ta, and Nb)
Soft X-ray absorption and emission measurements are performed for the K- edge
of B in MB (M=Mg, Al, Ta and Nb). Unique feature of MgB with a high
density of B 2-state below and above the Fermi edge, which
extends to 1 eV above the edge, is confirmed. In contrast, the B 2 density
of states in AlB and TaB, both of occupied and unoccupied states,
decreased linearly towards the Fermi energy and showed a dip at the Fermi
energy. Furthermore, there is a broadening of the peaks with
-character in XES and XAS of AlB, which is due to the increase of
three dimensionality in the -band in AlB. The DOS of NbB has a
dip just below the Fermi energy. The present results indicate that the large
DOS of B-2 states near the Fermi energy are crucial for the
superconductivity of MgB.Comment: 3 pages text and 4 pages figures. accepted for publication to Phys.
Rev.
Soft x-ray spectroscopy measurements of the p-like density of states of B in MgB2 and evidence for surface boron oxides on exposed surfaces
Soft X-ray absorption and fluorescence measurements are reported for the
K-edge of B in MgB2. The measurements confirm a high density of B
pxy(sigma)-states at the Fermi edge and extending to approximately 0.9 eV above
the edge. A strong resonance is observed in elastic scattering through a
core-exciton derived from out-of-plane pz(pi*)-states. Another strong
resonance, observed in both elastic and inelastic spectra, is identified as a
product of surface boron oxides.Comment: 7 pages total, 4 figures, submitted to Phys. Rev. Let
Electron Correlation Effects in Resonant Inelastic X-ray Scattering of NaV2O5
Element- and site-specific resonant inelastic x-ray scattering spectroscopy
(RIXS) is employed to investigate electron correlation effects in {}. In contrast to single photon techniques, RIXS at the vanadium
edge is able to probe transitions between V d-bands. A sharp energy
loss feature is observed at -1.56 eV, which is well reproduced by a model
calculation including correlation effects. The calculation identifies the loss
feature as excitation between the lower and upper Hubbard bands and permits an
accurate determination of the Hubbard interaction term eV.Comment: 15 pages, four figures, accepted to Phys. Rev. Let
Magnetic-field-induced singularities in spin dependent tunneling through InAs quantum dots
Current steps attributed to resonant tunneling through individual InAs
quantum dots embedded in a GaAs-AlAs-GaAs tunneling device are investigated
experimentally in magnetic fields up to 28 T. The steps evolve into strongly
enhanced current peaks in high fields. This can be understood as a
field-induced Fermi-edge singularity due to the Coulomb interaction between the
tunneling electron on the quantum dot and the partly spin polarized Fermi sea
in the Landau quantized three-dimensional emitter.Comment: 5 pages, 4 figure
Orbital Symmetry of Ba(Fe1-xCox)2As2 Superconductors Probed with X-ray Absorption Spectroscopy
The orbital symmetries of electron doped iron-arsenide superconductors
Ba(Fe1-xCox)2As2 have been measured with x-ray absorption spectroscopy. The
data reveal signatures of Fe d electron itinerancy, weak electronic
correlations, and a high degree of Fe-As hybridization related to the bonding
topology of the Fe dxz+yz states, which are found to contribute substantially
at the Fermi level. The energies and detailed orbital character of Fe and As
derived unoccupied s and d states are found to be in remarkably good agreement
with the predictions of standard density functional theory.Comment: Accepted for publication in Phys. Rev. B, 3 figures. Minor
corrections adde
Electronic Structure of B-2p State in AlB2 Single Crystal: Direct Observation ofp\sigma and p\pi Density of States
X-ray emission (XES) and absorption (XAS) spectra near the B- edge were
measured on single-crystalline AlB compound which is an isostructural
diboride of superconducting MgB. The partial density of states (PDOS) of
B-2 and orbitals were derived from the polarization dependence
of XES and XAS spectra. There are considerable amounts of PDOS near the Fermi
energy in AlB similarly to that in MgB, but there are almost no PDOS in
orbitals of AlB near the Fermi energy, i.e., a pseudo-gap in
state and a broad metallic state in state are observed. The
present result indirectly supports scenarios that the holes play an
important role in the occurrence of superconductivity in MgB. The overall
features of PDOS were found to be in good agreement with the result of band
calculation of AlB, but a small discrepancy in the Fermi energy is
observed, which is attributed to the Al vacancy in the compounds, i.e., the
estimated concentration is AlB.Comment: LaTeX files and 4 eps figures, to be published in J. Phys. Soc. Jp
Electronic structure of MgB: X-ray emission and absorption studies
Measurements of x-ray emission and absorption spectra of the constituents of
MgB are presented. The results obtained are in good agreement with
calculated x-ray spectra, with dipole matrix elements taken into account. The
comparison of x-ray emission spectra of graphite, AlB, and MgB in the
binding energy scale supports the idea of charge transfer from to
bands, which creates holes at the top of the bonding bands and
drives the high-TComment: final version as published in PR
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