424 research outputs found
Theoretical investigation of the evolution of the topological phase of BiSe under mechanical strain
The topological insulating phase results from inversion of the band gap due
to spin-orbit coupling at an odd number of time-reversal symmetric points. In
BiSe, this inversion occurs at the point. For bulk
BiSe, we have analyzed the effect of arbitrary strain on the
point band gap using Density Functional Theory. By computing the band structure
both with and without spin-orbit interactions, we consider the effects of
strain on the gap via Coulombic interaction and spin-orbit interaction
separately. While compressive strain acts to decrease the Coulombic gap, it
also increases the strength of the spin-orbit interaction, increasing the
inverted gap. Comparison with BiTe supports the conclusion that effects
on both Coulombic and spin-orbit interactions are critical to understanding the
behavior of topological insulators under strain, and we propose that the
topological insulating phase can be effectively manipulated by inducing strain
through chemical substitution
Electron-spectroscopic investigation of metal-insulator transition in Sr2Ru1-xTixO4 (x=0.0-0.6)
We investigate the nature and origin of the metal-insulator transition in
Sr2Ru1-xTixO4 as a function of increasing Ti content (x). Employing detailed
core, valence, and conduction band studies with x-ray and ultraviolet
photoelectron spectroscopies along with Bremsstrahlung isochromat spectroscopy,
it is shown that a hard gap opens up for Ti content greater than equal to 0.2,
while compositions with x<0.2 exhibit finite intensity at the Fermi energy.
This establishes that the metal-insulator transition in this homovalent
substituted series of compounds is driven by Coulomb interaction leading to the
formation of a Mott gap, in contrast to transitions driven by disorder effects
or band flling.Comment: Accepted for publication in Phys. Rev.
Effects of tin phosphate nanosheet addition on proton-conducting properties of sulfonated poly(ether sulfone) membranes
Organic/inorganic composite membranes were prepared by dispersing nanosheets of layered tin phosphate
hydrate [Sn(HPO4)2·nH2O (SnP)] in sulfonated poly(ether sulfone) (SPES) at SnP contents of 0–40 vol.%.
The stabilities and proton conductivities of SPES/SnP nanosheet (SnP-NS) composite membraneswere investigated
and comparedwith those of SPES/SnP particle (SnP-P) composite membranes. The chemical stabilities as evaluated
by thermogravimetry, differential thermal analysis, and diffuse reflectance Fourier-transform infrared spectroscopy
were improved in both composite membranes. The improvement in the structural stability of SPES/SnP-NS composite
membranes was more evident than that in SPES/SnP-P. The results suggest that exfoliation of SnP increases
the area of the SPES–SnP interface and extends the connectivity of the network of hydrogen bonds. A composite
membrane containing 10 vol.% SnP-NS (SPES/SnP-NS10vol.%) showed a high conductivity of 5.9×10−2 S cm−1
at 150 °C under saturated water vapor pressure. Although less water was present in SPES/SnP-NS10vol.% than in
SPES/SnP-P10vol.% or pure SPES, the conductivity of SnP-NS10vol.% was the highest among these samples at
130 °C under a high relative humidity (RH). However at a low RH, the proton-conducting property was not
improved by changing the composition of the SnP-NS. These results suggest that the hydrogen-bond network
operates effectively for proton conduction at a high RH, but at a low RH, the network fails to conduct as a result
of a decrease in water content accompanied by structural stabilization
The Morphological Changes in the Vestibular Sensory Epithelia Following Electrical Stimulation
The morphological changes of the vestibular sensory epithelia of the guinea pig following electrical stimulation were investigated using scanning electron microscope.
Positive and negative square wave pulse stimulation was given through a silver ball electrode placed on the round window membrane for one hour. The current intensities used were 100, 200 and 300 A.
While the direct current stimulation at intensities of 100 or 200 A did not cause any significant changes, severe damage of the utricular macula and the ampullar crista of the lateral semicircular canal was observed at 300 A. The degenerative changes such as fusion of sensory hairs, protrusion of the cuticular plate and loss of sensory cells were found on both the utricle and the semicircular canal. In the most severely damaged area, the sensory epithelial surface was badly torn apart.
In the clinical application of direct current to the inner ear for relieving tinnitus, special attention should be paid to the vestibular organ
Origin of magnetic moments and presence of a resonating valence bond state in BaYIrO
While it was speculated that 5 systems would possess non-magnetic
~=~0 ground state due to strong Spin-Orbit Coupling (SOC), all such systems
have invariably shown presence of magnetic moments so far. A puzzling case is
that of BaYIrO, which in spite of having a perfectly cubic structure
with largely separated Ir () ions, has consistently shown presence
of weak magnetic moments. Moreover, we clearly show from Muon Spin Relaxation
(SR) measurements that a change in the magnetic environment of the
implanted muons in BaYIrO occurs as temperature is lowered below 10~K.
This observation becomes counterintuitive, as the estimated value of SOC
obtained by fitting the RIXS spectrum of BaYIrO with an atomic
model is found to be as high as 0.39~eV, meaning that the system within this
model is neither expected to possess moments nor exhibit temperature dependent
magnetic response. Therefore we argue that the atomic coupling
description is not sufficient to explain the ground state of such systems,
where despite having strong SOC, presence of hopping triggers delocalisation of
holes, resulting in spontaneous generation of magnetic moments. Our theoretical
calculations further indicate that these moments favour formation of
spin-orbital singlets in the case of BaYIrO, which is manifested in
SR experiments measured down to 60~mK.Comment: 20 Pages, 7 Figure
Theoretical Investigation of the Evolution of the Topological Phase of Bi\u3csub\u3e2\u3c/sub\u3eSe\u3csub\u3e3\u3c/sub\u3e under Mechanical Strain
The topological insulating phase results from inversion of the band gap due to spin-orbit coupling at an odd number of time-reversal symmetric points. In Bi2Se3, this inversion occurs at the Γ point. For bulk Bi2Se3, we have analyzed the effect of arbitrary strain on the Γ point band gap using density functional theory. By computing the band structure both with and without spin-orbit interactions, we consider the effects of strain on the gap via Coulombic interaction and spin-orbit interaction separately. While compressive strain acts to decrease the Coulombic gap, it also increases the strength of the spin-orbit interaction, increasing the inverted gap. Comparison with Bi2Te3 supports the conclusion that effects on both Coulombic and spin-orbit interactions are critical to understanding the behavior of topological insulators under strain, and we propose that the topological insulating phase can be effectively manipulated by inducing strain through chemical substitution
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