22,724 research outputs found
Spin-current injection and detection in strongly correlated organic conductor
Spin-current injection into an organic semiconductor
film induced by the spin
pumping from an yttrium iron garnet (YIG) film. When magnetization dynamics in
the YIG film is excited by ferromagnetic or spin-wave resonance, a voltage
signal was found to appear in the
film.
Magnetic-field-angle dependence measurements indicate that the voltage signal
is governed by the inverse spin Hall effect in
. We found that the
voltage signal in the /YIG
system is critically suppressed around 80 K, around which magnetic and/or glass
transitions occur, implying that the efficiency of the spin-current injection
is suppressed by fluctuations which critically enhanced near the transitions
A time-dependent approach to electron pumping in open quantum systems
We propose a time-dependent approach to investigate the motion of electrons
in quantum pump device configurations. The occupied one-particle states are
propagated in real time and used to calculate the local electron density and
current. An advantage of the present computational scheme is that the same
computational effort is required to simulate monochromatic, polychromatic and
nonperiodic drivings. Furthermore, initial state dependence and history effects
are naturally accounted for. This approach can also be embedded in the
framework of time-dependent density functional theory to include
electron-electron interactions. In the special case of periodic drivings we
combine the Floquet theory with nonequilibrium Green's functions and obtain a
general expression for the pumped current in terms of inelastic transmission
probabilities. This latter result is used for benchmarking our propagation
scheme in the long-time limit. Finally, we discuss the limitations of
Floquet-based schemes and suggest our approach as a possible way to go beyond
them.Comment: 14 pages, 8 figure
A characterization of positive linear maps and criteria of entanglement for quantum states
Let and be (finite or infinite dimensional) complex Hilbert spaces. A
characterization of positive completely bounded normal linear maps from
into is given, which particularly gives a
characterization of positive elementary operators including all positive linear
maps between matrix algebras. This characterization is then applied give a
representation of quantum channels (operations) between infinite-dimensional
systems. A necessary and sufficient criterion of separability is give which
shows that a state on is separable if and only if
for all positive finite rank elementary operators
. Examples of NCP and indecomposable positive linear maps are given and
are used to recognize some entangled states that cannot be recognized by the
PPT criterion and the realignment criterion.Comment: 20 page
Absence of the London limit for the first-order phase transition to a color superconductor
We study the effects of gauge-field fluctuations on the free energy of a
homogeneous color superconductor in the color-flavor-locked (CFL) phase.
Gluonic fluctuations induce a strong first-order phase transition, in contrast
to electronic superconductors where this transition is weakly first order. The
critical temperature for this transition is larger than the one corresponding
to the diquark pairing instability. The physical reason is that the gluonic
Meissner masses suppress long-wavelength fluctuations as compared to the normal
conducting phase where gluons are massless, which stabilizes the
superconducting phase. In weak coupling, we analytically compute the
temperatures associated with the limits of metastability of the normal and
superconducting phases, as well as the latent heat associated with the
first-order phase transition. We then extrapolate our results to intermediate
densities and numerically evaluate the temperature of the fluctuation-induced
first-order phase transition, as well as the discontinuity of the diquark
condensate at the critical point. We find that the London limit of magnetic
interactions is absent in color superconductivity.Comment: 14 pages, 5 figure
Implementing the Simple Biosphere Model (SiB) in a general circulation model: Methodologies and results
The Simple Biosphere MOdel (SiB) of Sellers et al., (1986) was designed to simulate the interactions between the Earth's land surface and the atmosphere by treating the vegetation explicitly and relistically, thereby incorporating biophysical controls on the exchanges of radiation, momentum, sensible and latent heat between the two systems. The steps taken to implement SiB in a modified version of the National Meteorological Center's spectral GCM are described. The coupled model (SiB-GCM) was used with a conventional hydrological model (Ctl-GCM) to produce summer and winter simulations. The same GCM was used with a conventional hydrological model (Ctl-GCM) to produce comparable 'control' summer and winter variations. It was found that SiB-GCM produced a more realistic partitioning of energy at the land surface than Ctl-GCM. Generally, SiB-GCM produced more sensible heat flux and less latent heat flux over vegetated land than did Ctl-GCM and this resulted in the development of a much deeper daytime planetary boundary and reduced precipitation rates over the continents in SiB-GCM. In the summer simulation, the 200 mb jet stream and the wind speed at 850 mb were slightly weakened in the SiB-GCM relative to the Ctl-GCM results and equivalent analyses from observations
Window on Higgs Boson: Fourth Generation Decays Revisited
Direct and indirect searches of the Higgs boson suggest that 113 GeV
170 GeV is likely. With the LEP era over and the
Tevatron Run II search via arduous, we revisit a case where
or jets could arise via strong pair
production. In contrast to 10 years ago, the tight electroweak constraint on
-- (hence --) splitting reduces FCNC
, rates, making naturally competitive.
Such a "cocktail solution" is precisely the mix that could evade the CDF search
for , and the may well be lurking below the top. In
light of the Higgs program, this two-in-one strategy should be pursued.Comment: 4 pages, RevTex, 4 eps figures, One more figure, version to be
published in Phys. Rev.
Lagrangian particle paths and ortho-normal quaternion frames
Experimentalists now measure intense rotations of Lagrangian particles in
turbulent flows by tracking their trajectories and Lagrangian-average velocity
gradients at high Reynolds numbers. This paper formulates the dynamics of an
orthonormal frame attached to each Lagrangian fluid particle undergoing
three-axis rotations, by using quaternions in combination with Ertel's theorem
for frozen-in vorticity. The method is applicable to a wide range of Lagrangian
flows including the three-dimensional Euler equations and its variants such as
ideal MHD. The applicability of the quaterionic frame description to Lagrangian
averaged velocity gradient dynamics is also demonstrated.Comment: 9 pages, one figure, revise
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