33,697 research outputs found
Thermal activation energy of 3D vortex matter in NaFe1-xCoxAs (x=0.01, 0.03 and 0.07) single crystals
We report on the thermally activated flux flow dependency on the doping
dependent mixed state in NaFe1-xCoxAs (x=0.01, 0.03, and 0.07) crystals using
the magnetoresistivity in the case of B//c-axis and B//ab-plane. It was found
clearly that irrespective of the doping ratio, magnetoresistivity showed a
distinct tail just above the Tc, offset associated with the thermally activated
flux flow (TAFF) in our crystals. Furthermore, in TAFF region the temperature
dependence of the activation energy follows the relation U(T, B)=U_0 (B)
(1-T/T_c )^q with q=1.5 in all studied crystals. The magnetic field dependence
of the activation energy follows a power law of U_0 (B)~B^(-{\alpha}) where the
exponent {\alpha} is changed from a low value to a high value at a crossover
field of B=~2T, indicating the transition from collective to plastic pinning in
the crystals. Finally, it is suggested that the 3D vortex phase is the dominant
phase in the low-temperature region as compared to the TAFF region in our
series samples
Land use survey and mapping and water resources investigation in Korea
The author has identified the following significant results. Land use imagery is applicable to land use classification for small scale land use mapping less than 1:250,000. Land use mapping by satellite is more efficient and more cost-effective than land use mapping from conventional medium altitude aerial photographs. Six categories of level 1 land use classification are recognizable from MSS imagery. A hydrogeomorphological study of the Han River basin indicates that band 7 is useful for recognizing the soil and the weathering part of bed rock. The morphological change of the main river is accurately recognized and the drainage system in the area observed is easily classified because of the more or less simple rock type. Although the direct hydrological characteristics are not obtained from the MSS imagery, the indirect information such as the permeability of the soil and the vegetation cover, is helpful in interpreting the hydrological aspects
Kondo Effect and Josephson Current through a Quantum Dot between Two Superconductors
We investigate the supercurrent through a quantum dot for the whole range of
couplings using the numerical renormalization group method. We find that the
Josephson current switches abruptly from a - to a 0-phase as the coupling
increases. At intermediate couplings the total spin in the ground state depends
on the phase difference between the two superconductors. Our numerical results
can explain the crossover in the conductance observed experimentally by
Buitelaar \textit{et al.} [Phys. Rev. Lett. \textbf{89}, 256 801 (2002)].Comment: Fig.2 and corresponding text have been changed; Several other small
change
Singe ferroelectric and chiral magnetic domain of single-crystalline BiFeO in an electric field
We report polarized neutron scattering and piezoresponse force microscopy
studies of millimeter-sized single crystals of multiferroic BiFeO. The
crystals, grown below the Curie temperature, consist of a single ferroelectric
domain. Two unique electric polarization directions, as well as the populations
of equivalent spiral magnetic domains, can be switched reversibly by an
electric field. A ferroelectric monodomain with a single- single-helicity
spin spiral can be obtained. This level of control, so far unachievable in thin
films, makes single-crystal BiFeO a promising object for multiferroics
research.Comment: 4 figures in separate jpg file
Dielectric constants of Ir, Ru, Pt, and IrO2: Contributions from bound charges
We investigated the dielectric functions () of Ir, Ru, Pt,
and IrO, which are commonly used as electrodes in ferroelectric thin film
applications. In particular, we investigated the contributions from bound
charges (), since these are important scientifically as
well as technologically: the (0) of a metal electrode is one of
the major factors determining the depolarization field inside a ferroelectric
capacitor. To obtain (0), we measured reflectivity spectra of
sputtered Pt, Ir, Ru, and IrO2 films in a wide photon energy range between 3.7
meV and 20 eV. We used a Kramers-Kronig transformation to obtain real and
imaginary dielectric functions, and then used Drude-Lorentz oscillator fittings
to extract (0) values. Ir, Ru, Pt, and IrO produced
experimental (0) values of 4810, 8210, 5810, and
295, respectively, which are in good agreement with values obtained using
first-principles calculations. These values are much higher than those for
noble metals such as Cu, Ag, and Au because transition metals and IrO have
such strong d-d transitions below 2.0 eV. High (0) values will
reduce the depolarization field in ferroelectric capacitors, making these
materials good candidates for use as electrodes in ferroelectric applications.Comment: 26 pages, 6 figures, 2 table
CP Violation in the Top-Quark Pair Production at a Next Linear Collider
We provide a detailed, model-independent, study for CP violation effects due
to the T-odd top-quark electric dipole moment (EDM) and weak dipole moment
(WDM) in the top-quark pair production via and two-photon annihilation
at a next linear collider (NLC). There are two methods in detecting CP
violation effects in these processes. One method makes use of measurements of
various spin correlations in the final decay products of the produced top-quark
pair, while the other is to measure various CP-odd polarization asymmetry
effects of the initial states. In the case only the first method can
be used, and in the case both methods can be employed. We
provide a complete classification of angular correlations of the and
decay products under CP and CP\tilde{T} which greatly faciliate CP
tests in the mode. Concentrating on the second method with the Compton
back-scattered high-energetic laser light off the electron or positron beam in
the two-photon mode, we construct two CP-odd and CP\tilde{T}-even initial
polarization configurations and apply them to investigating CP-violating
effects due to the top-quark EDM. With a typical set of experimental parameters
at the NLC, we compare the 1-\sigma sensitivities to the top-quark EDM and WDM
in the mode and the two-photon mode. Some model expectation values of
the T-odd parameters are compared with the results.Comment: 45 pages(LaTeX), 10 eps figures, uses epsfig.st
InGaN nano-ring structures for high-efficiency light emitting diodes
A technique based on the Fresnel diffraction effect for the fabrication of nano-scale site-controlled ring structures in InGaN/GaN multi-quantum well structures has been demonstrated. The ring structures have an internal diameter of 500 nm and a wall width of 300 nm. A 1 cm-1 Raman shift has been measured, signifying substantial strain relaxation from the fabricated structure. The 9 nm blueshift observed in the cathodoluminescence spectra can be attributed to band filling and/or screening of the piezoelectric field. A light emitting diode based on this geometry has been demonstrated
Andreev Bound States in the Kondo Quantum Dots Coupled to Superconducting Leads
We have studied the Kondo quantum dot coupled to two superconducting leads
and investigated the subgap Andreev states using the NRG method. Contrary to
the recent NCA results [Clerk and Ambegaokar, Phys. Rev. B 61, 9109 (2000);
Sellier et al., Phys. Rev. B 72, 174502 (2005)], we observe Andreev states both
below and above the Fermi level.Comment: 5 pages, 5 figure
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