302 research outputs found
The band structure and Fermi surface of LaSrMnO thin films studied by in-situ angle-resolved photoemission spectroscopy
We have performed an in situ angle-resolved photoemission spectroscopy
(ARPES) on single-crystal surfaces of LaSrMnO (LSMO) thin
films grown on SrTiO (001) substrates by laser molecular beam epitaxy,
and investigated the electronic structure near the Fermi level (). The
experimental results were compared with the band-structure calculation based on
LDA + . The band structure of LSMO thin films consists of several highly
dispersive O 2 derived bands in the binding energy range of 2.0 - 6.0 eV and
Mn 3 derived bands near . ARPES spectra around the point show
a dispersive band near indicative of an electron pocket centered at the
point, although it was not so clearly resolved as an electronlike
pocket due to the suppression of spectral weight in the vicinity of .
Compared with the band-structure calculation, the observed conduction band is
assigned to the Mn 3 majority-spin band responsible for the
half-metallic nature of LSMO. We have found that the estimated size of the
Fermi surface is consistent with the prediction of the band-structure
calculation, while the band width becomes significantly narrower than the
calculation. Also, the intensity near is strongly reduced. The origin
of these discrepancies between the experiment and the calculation is discussed.Comment: 7 pages, 5 figure
Hole Transport in p-Type ZnO
A two-band model involving the A- and B-valence bands was adopted to analyze
the temperature dependent Hall effect measured on N-doped \textit{p}-type ZnO.
The hole transport characteristics (mobilities, and effective Hall factor) are
calculated using the ``relaxation time approximation'' as a function of
temperature. It is shown that the lattice scattering by the acoustic
deformation potential is dominant. In the calculation of the scattering rate
for ionized impurity mechanism, the activation energy of 100 or 170 meV is used
at different compensation ratios between donor and acceptor concentrations. The
theoretical Hall mobility at acceptor concentration of
cm is about 70 cmVs with the activation energy of 100 meV
and the compensation ratio of 0.8 at 300 K. We also found that the compensation
ratios conspicuously affected the Hall mobilities.Comment: 5page, 5 figures, accepted for publication in Jpn. J. Appl. Phy
Gradual Disappearance of the Fermi Surface near the Metal-Insulator Transition in LaSrMnO
We report the first observation of changes in the electronic structure of
LaSrMnO (LSMO) across the filling-control metal-insulator
(MI) transition by means of in situ angle-resolved photoemission spectroscopy
(ARPES) of epitaxial thin films. The Fermi surface gradually disappears near
the MI transition by transferring the spectral weight from the coherent band
near the Fermi level () to the lower Hubbard band, whereas a pseudogap
behavior also exists in the ARPES spectra in the close vicinity of for
the metallic LSMO. These results indicate that the spectral weight transfer
derived from strong electron-electron interaction dominates the gap formation
in LSMO associated with the filling-control MI transition.Comment: 11 pages, 4 figure
In-situ photoemission study of Pr_{1-x}Ca_xMnO_3 epitaxial thin films with suppressed charge fluctuations
We have performed an {\it in-situ} photoemission study of Pr_{1-x}Ca_xMnO_3
(PCMO) thin films grown on LaAlO_3 (001) substrates and observed the effect of
epitaxial strain on the electronic structure. We found that the chemical
potential shifted monotonically with doping, unlike bulk PCMO, implying the
disappearance of incommensurate charge fluctuations of bulk PCMO. In the
valence-band spectra, we found a doping-induced energy shift toward the Fermi
level (E_F) but there was no spectral weight transfer, which was observed in
bulk PCMO. The gap at E_F was clearly seen in the experimental band dispersions
determined by angle-resolved photoemission spectroscopy and could not be
explained by the metallic band structure of the C-type antiferromagnetic state,
probably due to localization of electrons along the ferromagnetic chain
direction or due to another type of spin-orbital ordering.Comment: 5 pages, 4 figure
Spin-filter tunnel junction with matched Fermi surfaces
Efficient injection of spin-polarized current into a semiconductor is a basic
prerequisite for building semiconductor-based spintronic devices. Here, we use
inelastic electron tunneling spectroscopy to show that the efficiency of
spin-filter-type spin injectors is limited by spin scattering of the tunneling
electrons. By matching the Fermi-surface shapes of the current injection source
and target electrode material, spin injection efficiency can be significantly
increased in epitaxial ferromagnetic insulator tunnel junctions. Our results
demonstrate that not only structural but also Fermi-surface matching is
important to suppress scattering processes in spintronic devices.Comment: 5 pages, 4 figure
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