471 research outputs found
What Determines Actual Use of Mobile Web Browsing Services? A Contextual Study in Korea
The use of mobile Web browsing services is a worldwide phenomenon. The intent of this research is to produce a testable model of Web browsing services use that both identifies unique national market differences and yet is theoretically parsimonious enough to permit future cross-national studies. Specifically, our model examines which factors determine the use of mobile Web browsing services in South Korea. We show that content quality, hardware quality, ubiquity, cost, and relational factors are important predictors of actual use of mobile Web browsing services. However, counter to our model’s predictions, network quality and security did not appear to be significant factors in Korea at this point of market maturity. Future empirical examination of the proposed model in different markets worldwide should provide multinational IT vendors with better understanding of the similarities and differences in the global smart phone business
Localized tachyon condensation and G-parity conservation
We study the condensation of localized tachyon in non-supersymmetric orbifold
{\C^2/\Z_n}. We first show that the G-parities of chiral primaries are
preserved under the condensation of localized tachyon(CLT) given by the chiral
primaries. Using this, we finalize the proof of the conjecture that the
lowest-tachyon-mass-squared increases under CLT at the level of type II string
with full consideration of GSO projection. We also show the equivalence between
the -parity given by coming from partition function
and that given by coming from the monomial
construction for the chiral primaires in the dual mirror picture.Comment: 12 pages, 2 figures, final form to appear in JHE
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
Charge-spin correlation in van der Waals antiferromagenet NiPS3
Strong charge-spin coupling is found in a layered transition-metal
trichalcogenide NiPS3, a van derWaals antiferromagnet, from our study of the
electronic structure using several experimental and theoretical tools:
spectroscopic ellipsometry, x-ray absorption and photoemission spectroscopy,
and density-functional calculations. NiPS3 displays an anomalous shift in the
optical spectral weight at the magnetic ordering temperature, reflecting a
strong coupling between the electronic and magnetic structures. X-ray
absorption, photoemission and optical spectra support a self-doped ground state
in NiPS3. Our work demonstrates that layered transition-metal trichalcogenide
magnets are a useful candidate for the study of correlated-electron physics in
two-dimensional magnetic material.Comment: 6 pages, 3 figur
Size Dependence of Metal-Insulator Transition in Stoichiometric Fe3O4 Nanocrystals
Magnetite (Fe3O4) is one of the most actively studied materials with a famous
metal-insulator transition (MIT), so-called the Verwey transition at around 123
K. Despite the recent progress in synthesis and characterization of Fe3O4
nanocrystals (NCs), it is still an open question how the Verwey transition
changes on a nanometer scale. We herein report the systematic studies on size
dependence of the Verwey transition of stoichiometric Fe3O4 NCs. We have
successfully synthesized stoichiometric and uniform-sized Fe3O4 NCs with sizes
ranging from 5 to 100 nm. These stoichiometric Fe3O4 NCs show the Verwey
transition when they are characterized by conductance, magnetization, cryo-XRD,
and heat capacity measurements. The Verwey transition is weakly size-dependent
and becomes suppressed in NCs smaller than 20 nm before disappearing completely
for less than 6 nm, which is a clear, yet highly interesting indication of a
size effect of this well-known phenomena. Our current work will shed new light
on this ages-old problem of Verwey transition.Comment: 18 pages, 4 figures, Nano Letters (accepted
Spin-orbit coupling effects on spin-phonon coupling in Cd2Os2O7
Spin-orbit coupling (SOC) is essential in understanding the properties of 5d
transition metal compounds, whose SOC value is large and almost comparable to
other key parameters. Over the past few years, there have been numerous studies
on the SOC-driven effects of the electronic bands, magnetism, and spin-orbit
entanglement for those materials with a large SOC. However, it is less studied
and remains an unsolved problem in how the SOC affects the lattice dynamics.
We, therefore, measured the phonon spectra of 5d pyrochlore Cd2Os2O7 over the
full Brillouin zone to address the question by using inelastic x-ray scattering
(IXS). Our main finding is a visible mode-dependence in the phonon spectra,
measured across the metal-insulator transition at 227 K. We examined the SOC
strength dependence of the lattice dynamics and its spin-phonon (SP) coupling,
with first-principle calculations. Our experimental data taken at 100 K are in
good agreement with the theoretical results obtained with the optimized U = 2.0
eV with SOC. By scaling the SOC strength and the U value in the DFT
calculations, we demonstrate that SOC is more relevant than U to explaining the
observed mode-dependent phonon energy shifts with temperature. Furthermore, the
temperature dependence of the phonon energy can be effectively described by
scaling SOC. Our work provides clear evidence of SOC producing a non-negligible
and essential effect on the lattice dynamics of Cd2Os2O7 and its SP coupling.Comment: 12 pages, 5 figures, accepted for publication at Rapid Communication
in Physical Review
Properties of spin 1/2 triangular lattice antiferromagnets: CuRE2Ge2O8 (RE=Y, La)
We found new two-dimensional (2D) quantum (S=1/2) antiferromagnetic systems:
CuRE2Ge2O8 (RE=Y and La). According to our analysis of high-resolution X-ray
and neutron diffraction experiments, the Cu-network of CuRE2Ge2O8 (RE=Y and La)
exhibits a 2D triangular lattice linked via weak bonds along the perpendicular
b-axis. Our bulk characterizations from 0.08 to 400 K show that they undergo a
long-range order at 0.51(1) and 1.09(4) K for the Y and La systems,
respectively. Interestingly, they also exhibit field induced phase transitions.
For theoretical understanding, we carried out the density functional theory
(DFT) band calculations to find that they are typical charge-transfer-type
insulators with a gap of Eg = 2 eV. Taken together, our observations make
CuRE2Ge2O8 (RE=Y and La) additional examples of low-dimensional quantum spin
triangular antiferromagnets with the low-temperature magnetic ordering.Comment: 15 pages, 6 figures, and 1 tabl
p-Brane cosmology and phases of Brans-Dicke theory with matter
We study the effect of the solitonic degrees of freedom in string cosmology
following the line of Rama. The gas of solitonic p-brane is treated as a
perfect fluid in a Brans-Dicke type theory. In this paper, we find exact
cosmological solutions for any Brans-Dicke parameter and for general
parameter of equation of state and classify the cosmology of the
solutions on a parameter space of and .Comment: 26 pages, 5 figures, Contents and references added; published in
Phys. Rev. D57(1998) 462
Microwave Spin Control of a Tin-Vacancy Qubit in Diamond
The negatively charged tin-vacancy (SnV-) center in diamond is a promising
solid-state qubit for applications in quantum networking due to its high
quantum efficiency, strong zero phonon emission, and reduced sensitivity to
electrical noise. The SnV- has a large spin-orbit coupling, which allows for
long spin lifetimes at elevated temperatures, but unfortunately suppresses the
magnetic dipole transitions desired for quantum control. Here, by use of a
naturally strained center, we overcome this limitation and achieve
high-fidelity microwave spin control. We demonstrate a pi-pulse fidelity of up
to 99.51+/0.03%$ and a Hahn-echo coherence time of T2echo = 170.0+/-2.8
microseconds, both the highest yet reported for SnV- platform. This performance
comes without compromise to optical stability, and is demonstrated at 1.7
Kelvin where ample cooling power is available to mitigate drive induced
heating. These results pave the way for SnV- spins to be used as a building
block for future quantum technologies
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