2,691 research outputs found
Spin polarization amplification within nonmagnetic semiconductors at room temperature
We demonstrate theoretically that the spin polarization of current can be
electrically amplified within nonmagnetic semiconductors by exploiting the fact
the spin current, compared to the charge current, is weakly perturbed by
electric driving forces. As a specific example, we consider a T-shaped current
branching geometry made entirely of a nonmagnetic semiconductor, where the
current is injected into one of the branches (input branch) and splits into the
other two branches (output branches). We show that when the input current has a
moderate spin polarization, the spin polarization in one of the output branches
can be higher than the spin polarization in the input branch and may reach 100%
when the relative magnitudes of current-driving electric fields in the two
output branches are properly tuned. The proposed amplification scheme does not
use ferromagnets or magnetic fields, and does not require low temperature
operation, providing an efficient way to generate a highly spin polarized
current in nonmagnetic semiconductors at room temperature.Comment: 11 pages, 2 figures, to appear in Phys. Rev.
Influence of Rb/Cs cation-exchange on inorganic Sn halide perovskites: From chemical structure to physical properties
CsSnI3 is a potential lead-free inorganic perovskite for solar energy applications due to its nontoxicity and attractive optoelectronic properties. Despite these advantages, photovoltaic cells using CsSnI3 have not been successful to date, in part due to low stability. We demonstrate how gradual substitution of Rb for Cs influences the structural, thermodynamic, and electronic properties on the basis of first-principles density functional theory calculations. By examining the effect of the Rb:Cs ratio, we reveal a correlation between octahedral distortion and band gap, including spin–orbit coupling. We further highlight the cation-induced variation of the ionization potential (work function) and the importance of surface termination for tin-based halide perovskites for engineering high-performance solar cells
Optical spectroscopic investigation on the coupling of electronic and magnetic structure in multiferroic hexagonal RMnO3 (R = Gd, Tb, Dy, and Ho) thin films
We investigated the effects of temperature and magnetic field on the
electronic structure of hexagonal RMnO3 (R = Gd, Tb, Dy, and Ho) thin films
using optical spectroscopy. As the magnetic ordering of the system was
disturbed, a systematic change in the electronic structure was commonly
identified in this series. The optical absorption peak near 1.7 eV showed an
unexpectedly large shift of more than 150 meV from 300 K to 15 K, accompanied
by an anomaly of the shift at the Neel temperature. The magnetic field
dependent measurement clearly revealed a sizable shift of the corresponding
peak when a high magnetic field was applied. Our findings indicated strong
coupling between the magnetic ordering and the electronic structure in the
multiferroic hexagonal RMnO3 compounds.Comment: 16 pages including 4 figure
model with Hopf term and fractional spin statistics
We reconsider the model with the Hopf term by using the
Batalin-Fradkin-Tyutin (BFT) scheme, which is an improved version of the Dirac
quantization method. We also perform a semi-classical quantization of the
topological charge Q sector by exploiting the collective coordinates to
explicitly show the fractional spin statistics.Comment: 15 page
Pressure dependence of upper critical fields in FeSe single crystals
We investigate the pressure dependence of the upper critical fields
({\mu}) for FeSe single crystals with pressure up to 2.57 GPa.
The superconducting (SC) properties show a disparate behavior across a critical
pressure where the pressure-induced antiferromagnetic phase coexists with
superconductivity. The magnetoresistance for and is very
different: for , magnetic field induces and enhances a hump in the
resistivity close to the for pressures higher than 1.2 GPa, while it is
absent for . Since the measured {\mu} for FeSe samples is
smaller than the orbital limited upper critical field ()
estimated by the Werthamer Helfand and Hohenberg (WHH) model, the Maki
parameter ({\alpha}) related to Pauli spin-paramagnetic effects is additionally
considered to describe the temperature dependence of {\mu}().
Interestingly, the {\alpha} value is hardly affected by pressure for ,
while it strongly increases with pressure for . The pressure evolution of
the {\mu}(0)s for the FeSe single crystals is found to be almost
similar to that of (), suggesting that the pressure-induced magnetic
order adversely affects the upper critical fields as well as the SC transition
temperature.Comment: 23 pages, 6 figures, 1 tabl
Electronic structures of hexagonal RMnO3 (R = Gd, Tb, Dy, and Ho) thin films
We investigated the electronic structure of multiferroic hexagonal RMnO3 (R =
Gd, Tb, Dy, and Ho) thin films using both optical spectroscopy and
first-principles calculations. Using artificially stabilized hexagonal RMnO3,
we extended the optical spectroscopic studies on the hexagonal multiferroic
manganite system. We observed two optical transitions located near 1.7 eV and
2.3 eV, in addition to the predominant absorption above 5 eV. With the help of
first-principles calculations, we attribute the low-lying optical absorption
peaks to inter-site transitions from the oxygen states hybridized strongly with
different Mn orbital symmetries to the Mn 3d3z2-r2 state. As the ionic radius
of the rare earth ion increased, the lowest peak showed a systematic increase
in its peak position. We explained this systematic change in terms of a
flattening of the MnO5 triangular bipyramid
Cost-utility of ferric carboxymaltose (Ferinject®) for iron-deficiency anemia patients with chronic heart failure in South Korea
A Flight Mechanics-Centric Review of Bird-Scale Flapping Flight
This paper reviews the flight mechanics and control of birds and bird-size aircraft. It is intended to fill a niche in the current survey literature which focuses primarily on the aerodynamics, flight dynamics and control of insect scale flight. We review the flight mechanics from first principles and summarize some recent results on the stability and control of birds and bird-scale aircraft. Birds spend a considerable portion of their flight in the gliding (i.e., non-flapping) phase. Therefore, we also review the stability and control of gliding flight, and particularly those aspects which are derived from the unique control features of birds
Production of pyroligneous acid from lignocellulosic biomass and their effectiveness against biological attacks
Pyroligneous acid which is one of the commercial sources for acetic acid can be produced from high temperature carbonization of lignocellulosic biomass. Acetic acid can be used as a wood preservative to discourage the growth of fungal and molds. However, at higher temperature, organic compounds especially acetic acid in pyroligneous acid degraded except for some phenols. Therefore, effectiveness pyroligneous acid that pyrolysed at different temperature as fungicide and insecticide for used as wood preservative was evaluated. Pyroligneous acids were derived from rubberwood, oil palm trunk and mix hardwood heated at temperature of 300, 400 and 500°C, respectively in an airless container. The yield of pyroligneous acids was calculated and the chemical compounds of the pyroligneous acid were analysed using Fourier Transform InfraRed (FT-IR). For the efficacy of pyroligneous acid tests, rubberwood test blocks were immersed in the pyroligneous acid for 24 h at room temperature. The treated rubberwood test blocks were later tested against mold (Penicillium sp.), white rot fungus (Pycnoporous sanguineus) and subterranean termites, (Coptotermes curvignathus) according to ASTM standard method. The result shows that highest pyroligneous acid yield was found during pyrolysed of lignocellulosic biomass at temperature of 500°C. All the rubberwood test blocks treated with pyroligneous acids were effective against the mold, white rot fungi and termites. Nonetheless, the pyrolysis temperature did not affect the effectiveness of pyroligneous acids against biological agents. Conclusively, pyroligneous acids effective for discourage the growth of mold and white rot fungi as well accelerate the mortality of termites in laboratory condition
Forest Decline Under Progress in the Urban Forest of Seoul, Central Korea
Vegetation in the urban area showed not only a difference in species composition but also lower diversity compared with that of the natural area. Successional trend was normal in natural area, but that in urban areas showed a retrogressive pattern. Korean mountain ash (Sorbus alnifolia (Siebold & Zucc.) K.Koch), a shade intolerant species, dominated such a retrogressive succession. The vegetation decline is due to changes of mesoclimate and soil properties that imbalanced distribution of green space induced as the result of urbanization. In recent years, new environmental stress due to climate change is imposed additively to this forest decline. Drought is the very environmental stress. Drought-induced plant damage started from withering of leaves of plants introduced for landscaping in the urban area. Over time, branches died and death of the whole plant body followed. In particular, damage of Korean mountain ash, the product of retrogressive succession, was remarkable. As retrogressive succession has already progressed much, thus such phenomenon could be recognized as crisis of urban forest
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