9,818 research outputs found
Josephson and proximity effects on the surface of a topological insulator
We investigate Josephson and proximity effects on the surface of a
topological insulator on which superconductors and a ferromagnet are deposited.
The superconducting regions are described by the conventional BCS Hamiltonian,
rather than the superconducting Dirac Hamiltonian. Junction interfaces are
assumed to be dirty. We obtain analytical expressions of the Josephson current
and the proximity-induced anomalous Green's function on the topological
insulator. The dependence of the Josephson effect on the junction length, the
temperature, the chemical potential and the magnetization is discussed. It is
also shown that the proximity-induced pairing on the surface of a topological
insulator includes even and odd frequency triplet pairings as well as a
conventional s-wave one.Comment: 7 pages, 5 figure
Universal quantum computation with temporal-mode bilayer square lattices
We propose an experimental design for universal continuous-variable quantum
computation that incorporates recent innovations in linear-optics-based
continuous-variable cluster state generation and cubic-phase gate
teleportation. The first ingredient is a protocol for generating the
bilayer-square-lattice cluster state (a universal resource state) with temporal
modes of light. With this state, measurement-based implementation of Gaussian
unitary gates requires only homodyne detection. Second, we describe a
measurement device that implements an adaptive cubic-phase gate, up to a random
phase-space displacement. It requires a two-step sequence of homodyne
measurements and consumes a (non-Gaussian) cubic-phase state.Comment: (v2) 14 pages, 5 figures, consistent with published version; (v1) 13
pages, 5 figure
Statistical Study of the Reconnection Rate in Solar Flares Observed with YOHKOH/SXT
We report a statistical study of flares observed with the Soft X-ray
Telescope (SXT) onboard Yohkoh in the year of 2000. We measure physical
parameters of 77 flares, such as the temporal scale, the size, and the magnetic
flux density and find that the sizes of flares tend to be distributed more
broadly as the GOES class becomes weaker and that there is a lower limit of
magnetic flux density that depends on the GOES class. We also examine the
relationship between these parameters and find weak correlation between
temporal and spatial scales of flares. We estimate reconnection inflow
velocity, coronal Alfven velocity, and reconnection rate using above observed
values. The inflow velocities are distributed from a few km/s to several tens
km/s and the Alfven velocities in the corona are in the range from 10^3 to 10^4
km/s. Hence the reconnection rate is 10^-3 - 10^-2. We find that the
reconnection rate in a flare tends to decrease as the GOES class of the flare
increases. This value is within one order of magnitude from the theoretical
maximum value predicted by the Petschek model, although the dependence of the
reconnection rate on the magnetic Reynolds number tends to be stronger than
that in the Petschek model.Comment: 21 pages, 8 figures, accepted for publication in Ap
Multi-wavelength spectroscopic observation of EUV jet in AR 10960
We have studied the relationship between the velocity and temperature of a
solar EUV jet. The highly accelerated jet occurred in the active region NOAA
10960 on 2007 June 5. Multi-wavelength spectral observations with EIS/Hinode
allow us to investigate Doppler velocities at the wide temperature range. We
analyzed the three-dimensional angle of the jet from the stereoscopic analysis
with STEREO. Using this angle and Doppler velocity, we derived the true
velocity of the jet. As a result, we found that the cool jet observed with
\ion{He}{2} 256 \AA is accelerated to around which is over the upper limit of the chromospheric evaporation. The
velocities observed with the other lines are under the upper limit of the
chromospheric evaporation while most of the velocities of hot lines are higher
than that of cool lines. We interpret that the chromospheric evaporation and
magnetic acceleration occur simultaneously. A morphological interpretation of
this event based on the reconnection model is given by utilizing the
multi-instrumental observations.Comment: Accepted for publication in Ap
Role of Water Film in Weathering of Porous Rhyolite under Water Unsaturated Condition
AbstractTo study weathering behavior under water-unsaturated conditions, flow-through dissolution experiments using a porous rhyolite were performed under both saturated and unsaturated conditions. When water was passed into a dried rock core, water saturation rapidly increased to 0.3 in 2hours, and then reached 0.4 in 6 days. The proportion of the reactive surface area under the unsaturated condition to that under the saturated condition, Auns/As, was 0.46 after 1 day and increased to 0.90 in 6 days. Because Auns/As was always greater than water saturation, the surfaces of air- filled pores seemed to be wetted with a water film and dissolved. The water film thickness was estimated to be 2–3nm. The reason for Auns/As < 1 may be that the flushing efficiency of dissolved elements in the water film was not enough to keep the concentration far from equilibrium, and thereby the dissolution rate in the water film was decreased
Crossover of superconducting properties and kinetic-energy gain in two-dimensional Hubbard model
Superconductivity in the Hubbard model on a square lattice near half filling
is studied using an optimization (or correlated) variational Monte Carlo
method. Second-order processes of the strong-coupling expansion are considered
in the wave functions beyond the Gutzwiller factor. Superconductivity of
d_x^2-y^2-wave is widely stable, and exhibits a crossover around U=U_co\sim 12t
from a BCS type to a new type. For U\gsim U_co (U\lsim U_co), the energy gain
in the superconducting state is derived from the kinetic (potential) energy.
Condensation energy is large and \propto exp(-t/J) [tiny] on the strong [weak]
coupling side of U_co. Cuprates belong to the strong-coupling regime.Comment: 4 pages, 6 figure
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