294 research outputs found
Epitaxial growth and transport properties of Nb-doped SrTiO thin films
Nb-doped SrTiO epitaxial thin films have been prepared on (001)
SrTiO substrates using pulsed laser deposition. A high substrate
temperature () was found to be necessary to achieve
2-dimensional growth. Atomic force microscopy reveals atomically flat surfaces
with 3.9 \AA steps. The films show a metallic behavior, residual
resistivity ratios between 10 and 100, and low residual resistivity of the
order of 10cm. At 0.3 K, a sharp superconducting transition,
reaching zero resistance, is observed.Comment: 4 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
High Throughput Oxide Lattice Engineering by Parallel Laser Molecular Beam Epitaxy and Concurrent X-ray Diffraction
A novel laser molecular beam epitaxy (LMBE) system for the fabrication of
atomically controlled oxides superlattices and an x-ray diffractometer that
measures spatially-resolved x-ray diffraction spectra have been developed based
on the concept of combinatorial methodology. The LMBE chamber has two moving
masks, an automated target stage, a substrate heating laser, and an in-situ
scanning reflection high-energy electron diffraction system. The x-ray
diffractometer with a curved monochromator and two-dimensional detector is used
for rapid concurrent x-ray diffraction intensity mapping with the two axes of
the detector corresponding to the diffraction angle and a position in the
sample.Comment: 19pages, 9figure
Effect of strong localization of doped holes in angle-resolved photoemission spectra of LaSrFeO
We have performed an angle-resolved photoemission spectroscopy study of
LaSrFeO using {\it in situ} prepared thin films and
determined its band structure. The experimental band dispersions could be well
explained by an empirical band structure assuming the G-type antiferromagnetic
state. However, the Fe 3d bands were found to be shifted downward relative to
the Fermi level () by eV compared with the calculation and to
form a (pseudo)gap of eV at . We attribute this observation to a
strong localization effect of doped holes due to polaron formation.Comment: 5 pages, 5 figure
151Eu Mössbauer spectroscopy and x-ray-diffraction studies on the Pb2Ba2EuCu3O8+[delta] system
Simultaneous replacement of Sr by Ba and Y by Eu in the Pb-2213 system was found to yield single-phase Pb2Ba2EuCu3O8+δ samples, suitable for Eu151 Mössbauer measurements. The samples were synthesized by a solid-state reaction of metal oxides and carbonates under an inert atmosphere. An oxygen-rich sample corresponding to δ=1.79 was obtained by annealing the as-synthesized material (δ=0.16) in oxygen. The oxygen annealing increased the size of the lattice constants and led to an orthorhombic-to-tetragonal phase transition of the structure. The samples were also oriented in an 11.7-T magnetic field. The x-ray-diffraction spectra showed that the c axes tended to orient perpendicular to the applied field. The measured Mössbauer spectra exhibited an electric quadrupole interaction typical of the Eu site in high-Tc cuprates. The average orientation angles obtained from fittings of the Mössbauer spectra were in accordance with the results from the x-ray-diffraction measurements.Peer reviewe
Photoemission from buried interfaces in SrTiO3/LaTiO3 superlattices
We have measured photoemission spectra of SrTiO3/LaTiO3 superlattices with a
topmost SrTiO3 layer of variable thickness. Finite coherent spectral weight
with a clear Fermi cut-off was observed at chemically abrupt SrTiO3/LaTiO3
interfaces, indicating that an ``electronic reconstruction'' occurs at the
interface between the Mott insulator LaTiO3 and the band insulator SrTiO3. For
SrTiO3/LaTiO3 interfaces annealed at high temperatures (~ 1000 C), which leads
to Sr/La atomic interdiffusion and hence to the formation of La1-xSrxTiO3-like
material, the intensity of the incoherent part was found to be dramatically
reduced whereas the coherent part with a sharp Fermi cut-off is enhanced due to
the spread of charge. These important experimental features are well reproduced
by layer dynamical-mean-field-theory calculation
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