260 research outputs found
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
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
Hole-doping-induced changes in the electronic structure of LaSrFeO : soft x-ray photoemission and absorption study of epitaxial thin films
We have studied the electronic structure of epitaxially grown thin films of
LaSrFeO by {\it in-situ} photoemission spectroscopy (PES) and
x-ray absorption spectroscopy (XAS) measurements. The Fe 2 and valence-band
PES spectra and the O XAS spectra of LaFeO have been successfully
reproduced by configuration-interaction cluster-model calculation and, except
for the satellite structure, by band-structure calculation.From the shift of
the binding energies of core levels, the chemical potential was found to be
shifted downward as was increased. Among the three peaks in the
valence-band spectra of LaSrFeO, the peak nearest to the Fermi
level (), due to the `` band'', was found to move toward and
became weaker as was increased, whereas the intensity of the peak just
above in the O XAS spectra increased with . The gap or pseudogap
at was seen for all values of . These results indicate that changes in
the spectral line shape around are dominated by spectral weight transfer
from below to above across the gap and are therefore highly
non-rigid-band-like.Comment: 8 pages, 7 figure
Ab-initio electronic and magnetic structure in La_0.66Sr_0.33MnO_3: strain and correlation effects
The effects of tetragonal strain on electronic and magnetic properties of
strontium-doped lanthanum manganite, La_{2/3}Sr_{1/3}MnO_3 (LSMO), are
investigated by means of density-functional methods. As far as the structural
properties are concerned, the comparison between theory and experiments for
LSMO strained on the most commonly used substrates, shows an overall good
agreement: the slight overestimate (at most of 1-1.5 %) for the equilibrium
out-of-plane lattice constants points to possible defects in real samples. The
inclusion of a Hubbard-like contribution on the Mn d states, according to the
so-called "LSDA+U" approach, is rather ineffective from the structural point of
view, but much more important from the electronic and magnetic point of view.
In particular, full half-metallicity, which is missed within a bare
density-functional approach, is recovered within LSDA+U, in agreement with
experiments. Moreover, the half-metallic behavior, particularly relevant for
spin-injection purposes, is independent on the chosen substrate and is achieved
for all the considered in-plane lattice constants. More generally, strain
effects are not seen to crucially affect the electronic structure: within the
considered tetragonalization range, the minority gap is only slightly (i.e. by
about 0.1-0.2 eV) affected by a tensile or compressive strain. Nevertheless, we
show that the growth on a smaller in-plane lattice constant can stabilize the
out-of-plane vs in-plane e_g orbital and significatively change their relative
occupancy. Since e_g orbitals are key quantities for the double-exchange
mechanism, strain effects are confirmed to be crucial for the resulting
magnetic coupling.Comment: 16 pages, 7 figures, to be published on J. Phys.: Condensed Matte
Magnetic oxide semiconductors
Magnetic oxide semiconductors, oxide semiconductors doped with transition
metal elements, are one of the candidates for a high Curie temperature
ferromagnetic semiconductor that is important to realize semiconductor
spintronics at room temperature. We review in this paper recent progress of
researches on various magnetic oxide semiconductors. The magnetization,
magneto-optical effect, and magneto-transport such as anomalous Hall effect are
examined from viewpoint of feasibility to evaluate the ferromagnetism. The
ferromagnetism of Co-doped TiO2 and transition metal-doped ZnO is discussed.Comment: 26 pages, 5 tables, 6 figure
Feature selection for chemical sensor arrays using mutual information
We address the problem of feature selection for classifying a diverse set of chemicals using an array of metal oxide sensors. Our aim is to evaluate a filter approach to feature selection with reference to previous work, which used a wrapper approach on the same data set, and established best features and upper bounds on classification performance. We selected feature sets that exhibit the maximal mutual information with the identity of the chemicals. The selected features closely match those found to perform well in the previous study using a wrapper approach to conduct an exhaustive search of all permitted feature combinations. By comparing the classification performance of support vector machines (using features selected by mutual information) with the performance observed in the previous study, we found that while our approach does not always give the maximum possible classification performance, it always selects features that achieve classification performance approaching the optimum obtained by exhaustive search. We performed further classification using the selected feature set with some common classifiers and found that, for the selected features, Bayesian Networks gave the best performance. Finally, we compared the observed classification performances with the performance of classifiers using randomly selected features. We found that the selected features consistently outperformed randomly selected features for all tested classifiers. The mutual information filter approach is therefore a computationally efficient method for selecting near optimal features for chemical sensor arrays
Tumor-promoting functions of transforming growth factor-β in progression of cancer
Transforming growth factor-β (TGF-β) elicits both tumor-suppressive and tumor-promoting functions during cancer progression. Here, we describe the tumor-promoting functions of TGF-β and how these functions play a role in cancer progression. Normal epithelial cells undergo epithelial-mesenchymal transition (EMT) through the action of TGF-β, while treatment with TGF-β and fibroblast growth factor (FGF)-2 results in transdifferentiation into activated fibroblastic cells that are highly migratory, thereby facilitating cancer invasion and metastasis. TGF-β also induces EMT in tumor cells, which can be regulated by oncogenic and anti-oncogenic signals. In addition to EMT promotion, invasion and metastasis of cancer are facilitated by TGF-β through other mechanisms, such as regulation of cell survival, angiogenesis, and vascular integrity, and interaction with the tumor microenvironment. TGF-β also plays a critical role in regulating the cancer-initiating properties of certain types of cells, including glioma-initiating cells. These findings thus may be useful for establishing treatment strategies for advanced cancer by inhibiting TGF-β signaling
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