558 research outputs found
Coexistence of two- and three-dimensional Shubnikov-de Haas oscillations in Ar^+ -irradiated KTaO_3
We report the electron doping in the surface vicinity of KTaO_3 by inducing
oxygen-vacancies via Ar^+ -irradiation. The doped electrons have high mobility
(> 10^4 cm^2/Vs) at low temperatures, and exhibit Shubnikov-de Haas
oscillations with both two- and three-dimensional components. A disparity of
the extracted in-plane effective mass, compared to the bulk values, suggests
mixing of the orbital characters. Our observations demonstrate that Ar^+
-irradiation serves as a flexible tool to study low dimensional quantum
transport in 5d semiconducting oxides
Dominant mobility modulation by the electric field effect at the LaAlO_3 / SrTiO_3 interface
Caviglia et al. [Nature (London) 456, 624 (2008)] have found that the
superconducting LaAlO_3 / SrTiO_3 interface can be gate modulated. A central
issue is to determine the principal effect of the applied electric field. Using
magnetotransport studies of a gated structure, we find that the mobility
variation is almost five times as large as the sheet carrier density.
Furthermore, superconductivity can be suppressed at both positive and negative
gate bias. These results indicate that the relative disorder strength strongly
increases across the superconductor-insulator transition.Comment: 4 pages, 4 figure
PROPOSAL OF NEW K-FACTOR FUNCTION IN LIGHTNING IMPULSE TEST FOR ELECTRIC POWER EQUIPMENT
Ultra high voltage (UHV) systems are increasingly being planned and constructed, hence studies are promoted on the standard for high-voltage test techniques for UHV-class equipment. For the lightning impulse voltage test, a study is being conducted on the application of a method of evaluating the test waveform through conversion using the test voltage function (k-factor function) that was adopted in IEC 60060-1. The existing k-factor function was established based on the experimental results for more compact models, as compared with the insulating structure of UHV-class equipment, mainly with a breakdown voltage of about 100 kV. To determine whether this k-factor function can also be used for the test of UHV-class equipment, the experimental results for large-sized models were needed. In the present paper, to address this issue, the authors initially obtained k-factor values experimentally using the largest possible model (UHV model) assuming UHV-class equipment. Substantially, a study was conducted on a new k-factor function based on these experimental results. First, in the study, several ideas for the k-factor function were shown and applied to various waveforms to clarify their advantages and disadvantages. Next, in addition to these results, a study was conducted on a k-factor function suitable for UHV-class equipment with considering the actual UHV facilities. Consequently, it was concluded that the form of the function should be the same as that of the existing one but that it would be reasonable to adopt a relatively lower k-factor function for UHV-class equipment by revising the constant. Further, this new function could replace the existing one in 60060-1 for all voltage classes to consider the breakdown voltage ranges as a basis and LIWV (Lightning Impulse Withstand Voltage) values.20th International Symposium on High Voltage Engineering, August 28 - September 01, 2017, Buenos Aires, Argentin
Thickness dependence of the mobility at the LaAlO_3 / SrTiO_3 interface
The electronic transport properties of a series of LaAlO_3 / SrTiO_3
interfaces were investigated, and a systematic thickness dependence of the
sheet resistance and magnetoresistance was found for constant growth
conditions. This trend occurs above the critical thickness of four unit cells,
below which the LaAlO_3 / SrTiO_3 interface is not conducting. A dramatic
decrease in mobility of the electron gas of nearly two orders of magnitude was
observed with increasing LaAlO_3 thickness from five to 25 unit cells.Comment: 3 pages, 4 figures, submitted for publicatio
Termination Control of the Interface Dipole in LaSrMnO/Nb:SrTiO (001) Schottky Junctions
In order to investigate the interface termination dependence of perovskite
band alignments, we have studied the Schottky barrier height at
LaSrMnO/Nb:SrTiO (001) heterointerfaces. As the
Nb:SrTiO semiconductor was varied from TiO termination to SrO
termination by variable insertion of a SrMnO layer, a large systematic
increase in the Schottky barrier height was observed. This can be ascribed to
the evolution of the interface dipole induced to screen the polar discontinuity
at the interface, which gives a large internal degree of freedom for tuning
band diagrams in oxides.Comment: 10 pages, 5 figure
Characterization of the Schottky Barrier in SrRuO3/Nb:SrTiO3 Junctions
Internal photoemission spectroscopy was used to determine the Schottky
barrier height in rectifying SrRuO3/Nb-doped SrTiO3 junctions for 0.01 wt % and
0.5 wt % Nb concentrations. Good agreement was obtained with the barrier height
deduced from capacitance-voltage measurements, provided that a model of the
nonlinear permittivity of SrTiO3 was incorporated in extrapolating the built-in
potential, particularly for high Nb concentrations. Given the generic
polarizability of perovskites under internal/external electric fields, internal
photoemission provides a valuable independent probe of the interface electronic
structure.Comment: 15 pages, 3 figure
Magnetodielectric Coupling in Nonmagnetic Au/GaAs:Si Schottky Barriers
We report on a heretofore unnoted giant negative magnetocapacitance (>20%) in
non-magnetic Au/GaAs:Si Schottky barriers that we attribute to a magnetic field
in-duced increase in the binding energy of the shallow donor Si impurity atoms.
Depletion capacitance (Cdep) dispersion identifies the impurity ionization and
capture processes that give rise to a magnetic field dependent density of
ionized impurities. Internal photoemission experiments confirm that the large
field-induced shifts in the built-in potential, inferred from 1/Cdep^2 vs
voltage measurements, are not due to a field-dependent Schottky barrier height,
thus requiring a modification of the abrupt junction approximation that
accounts for the observed magnetodielectric coupling.Comment: 25 pages, 5 figures, submitted to Phys. Rev.
Ab-initio study of BaTiO3 surfaces
We have carried out first-principles total-energy calculations of (001)
surfaces of the tetragonal and cubic phases of BaTiO3. Both BaO-terminated
(type I) and TiO2-terminated (type II) surfaces are considered, and the atomic
configurations have been fully relaxed. We found no deep-gap surface states for
any of the surfaces, in agreement with previous theoretical studies. However,
the gap is reduced for the type-II surface, especially in the cubic phase. The
surface relaxation energies are found to be substantial, i.e., many times
larger than the bulk ferroelectric well depth. Nevertheless, the influence of
the surface upon the ferroelectric order parameter is modest; we find only a
small enhancement of the ferroelectricity near the surface.Comment: 8 pages, two-column style with 4 postscript figures embedded. Uses
REVTEX and epsf macros. Also available at
http://www.physics.rutgers.edu/~dhv/preprints/index.html#pad_sur
Micro/nanostructural properties of peri-implant jaw bones: a human cadaver study
PURPOSE: Many points concerning the structure of osseointegration and the surrounding jaw bone remain unclear, and its optimal histological form has yet to be identified. The aim of this study was to clarify the structural characteristics of peri-implant jaw bone on the micro- and nano-scales by quantitatively evaluating bone quality. METHODS: Five samples of human mandibular bone containing dental implants and one dentate sample that had been in place for some years while the donors were still alive were collected. Bulk staining was performed, and 100-μm-thick polished specimens were prepared. The osteon distributions in peri-implant bone and mandibular cortical bone were measured, after which alignment analysis of biological apatite (BAp) crystallites and anisotropy analysis of collagen fiber orientation using second-harmonic generation imaging were carried out. RESULTS: Osteons in the vicinity of the implant body ran parallel to it. In the cortical bone at the base of the mandible, however, most osteons were oriented mesiodistally. The preferential alignment of BAp crystallites was generally consistent with osteon orientation. The orientation of collagen fibers in peri-implant jaw bone resembled the concentric rings seen in normal cortical bone, but there were also fibers that ran orthogonally across these concentric fibers. CONCLUSIONS: These results suggest that the mechanical strain imposed by implants causes the growth of cortical bone-like bone in areas that would normally consist of cancellous bone around the implants, and that its structural characteristics are optimized for the load environment of the peri-implant jaw bone
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