3,553 research outputs found
The vortex dynamics of a Ginzburg-Landau system under pinning effect
It is proved that the vortices are attracted by impurities or inhomogeities
in the superconducting materials. The strong H^1-convergence for the
corresponding Ginzburg-Landau system is also proved.Comment: 23page
Upconversion of optical signals with multi-longitudinal-mode pump lasers
Multi-longitudinal-mode lasers have been believed to be good candidates as
pump sources for optical frequency conversion. However, we present a
semi-classical model for frequency conversion of optical signals with a
multimode pump laser, which shows that fluctuations of the instantaneous pump
power limit the conversion efficiency. In an experiment, we upconverted a 1550
nm optical signal in a periodically poled lithium niobate waveguide using with
a multi-longitudinal-mode laser, an observed a maximum conversion efficiency of
70%, in good agreement with our theoretical model. Compared to single-mode
pumping, multimode pumping is not a suitable technique for attaining stable
near-unity-efficiency frequency conversion. However, the results obtained here
could find application in characterization of the spectral or temporal
structure of multi-longitudinal-mode lasers.Comment: 6 pages, 4 figures, comments are welcome
Composite Polarons in Ferromagnetic Narrow-band Metallic Manganese Oxides
A new mechanism is proposed to explain the colossal magnetoresistance and
related phenomena. Moving electrons accompanied by Jahn-Teller phonon and
spin-wave clouds may form composite polarons in ferromagnetic narrow-band
manganites. The ground-state and finite-temperature properties of such
composite polarons are studied in the present paper. By using a variational
method, it is shown that the energy of the system at zero temperature decreases
with the formation of composite polaron; the energy spectrum and effective mass
of the composite polaron at finite temperature is found to be strongly
renormalized by the temperature and the magnetic field. It is suggested that
the composite polaron contribute significantly to the transport and the
thermodynamic properties in ferromagnetic narrow-band metallic manganese
oxides.Comment: Latex, no figur
Pairing Symmetry in Iron-Pnictide Superconductor KFeAs
The pairing symmetry is one of the major issues in the study of iron-based
superconductors. We adopt a low-energy effective kinetic model based on the
first-principles band structure calculations combined with the -
model for KFeAs, the phase diagram of pairing symmetries is
constructed. Putting the values of and of the - model
obtained by the first-principles calculations into this phase diagram, we find
that the pairing symmetry for KFeAs is a nodal -wave in the
folded Brillouin zone with two iron atoms per unit cell. This is in good
agreement with experiments observed a nodal order parameter.Comment: 5 pages, 4 figures (The pairing symmetry is dependent on choosing an
effective tight-binding model. In the publication version, we adopt a
ten-orbital model by using the maximally localized Wannier functions based on
the first-principles band structure calculations, and give an s-wave pairing
for KFeAs
Charge and Spin Transport in the One-dimensional Hubbard Model
In this paper we study the charge and spin currents transported by the
elementary excitations of the one-dimensional Hubbard model. The corresponding
current spectra are obtained by both analytic methods and numerical solution of
the Bethe-ansatz equations. For the case of half-filling, we find that the
spin-triplet excitations carry spin but no charge, while charge -spin
triplet excitations carry charge but no spin, and both spin-singlet and charge
-spin-singlet excitations carry neither spin nor charge currents.Comment: 24 pages, 14 figure
Quantum broadcast communication
Broadcast encryption allows the sender to securely distribute his/her secret
to a dynamically changing group of users over a broadcast channel. In this
paper, we just consider a simple broadcast communication task in quantum
scenario, which the central party broadcasts his secret to multi-receiver via
quantum channel. We present three quantum broadcast communication schemes. The
first scheme utilizes entanglement swapping and Greenberger-Horne-Zeilinger
state to realize a task that the central party broadcasts his secret to a group
of receivers who share a group key with him. In the second scheme, based on
dense coding, the central party broadcasts the secret to multi-receiver who
share each of their authentication key with him. The third scheme is a quantum
broadcast communication scheme with quantum encryption, which the central party
can broadcast the secret to any subset of the legal receivers
Quasiparticle Scattering Interference in (K,Tl)FexSe2 Superconductors
We model the quasiparticle interference (QPI) pattern in the recently
discovered (K,Tl)Fe_xSe2 superconductors. We show in the superconducting state
that, due to the absence of hole pockets at the Brillouin zone center, the
quasiparticle scattering occurs around the momentum transfer q=(0,0) and (\pm
\pi, \pm \pi) between electron pockets located at the zone boundary. More
importantly, although both d_{x^2-y^2}-wave and s-wave pairing symmetry lead to
nodeless quasiparticle excitations, distinct QPI features are predicted between
both types of pairing symmetry. In the presence of a nonmagnetic impurity
scattering, the QPI exhibits strongest scattering with q=(\pm \pi, \pm \pi) for
the d_{x^2-y^2}-wave pairing symmetry; while the strongest scattering exhibits
a ring-like structure centered around both q=(0,0) and (\pm \pi, \pm \pi) for
the isotropic s-wave pairing symmetry. A unique QPI pattern has also been
predicted due to a local pair-potential-type impurity scattering. The
significant contrast in the QPI pattern between the d_{x^2-y^2}-wave and the
isotropic s-wave pairing symmetry can be used to probe the pairing symmetry
within the Fourier-transform STM technique.Comment: 4+ pages, 3 embedded eps figure
Recommended from our members
Predicted and measured glass surface temperatures in an industrial, regeneratively gas-fired flat glass furnace
This study reports optically measured glass surface temperatures along the furnace center-line in the combustion space of a sideport, 455 (metric) t/d industrial, gas-fired flat glass furnace. The measurements were made using a water-cooled two-color pyrometer inserted through holes in the crown at six locations along the length of the furnace. Both average and time-resolved glass surface temperature measurements were performed during the approximately 20 s reversal period of the furnace. The measured glass surface temperature data are supplemented by observations of the batch location using a specially designed, water-cooled video probe. The average temperatures were found to rise from a low near 1700 Κ near the batch blanket to a peak of approximately 1900 K, then drop to a level of 1800 K. Evidence of batch Islands or "logs" is observed in the surface temperature data collected at the measurement location nearest the batch blanket. Large temperature excursions are seen here, indicative of measurement alternately of both the batch surface and the molten glass. Also reported in this study are results of a numerical model for the three-dimensional melt flow and heat transfer in the tank, coupled with a batch melting model. The radiant heat flux distribution incident on the melt and batch blanket surfaces is assumed. The melt tank model includes bubbling. The numerical predictions agree well with the timeaveraged glass surface temperature data collected experimentally The measurements and model predictions illustrate the complex transport phenomena in the melting section of the furnace
Phase diagram of a Bose-Fermi mixture in a one-dimensional optical lattice in terms of fidelity and entanglement
We study the ground-state phase diagram of a Bose-Fermi mixture loaded in a
one-dimensional optical lattice by computing the ground-state fidelity and
quantum entanglement. We find that the fidelity is able to signal quantum phase
transitions between the Luttinger liquid phase, the density-wave phase, and the
phase separation state of the system; and the concurrence can be used to signal
the transition between the density-wave phase and the Ising phase.Comment: 4 pages 3 figure
- …