6,432 research outputs found
Shot noise in ferromagnet--normal metal systems
A semiclassical theory of the low frequency shot noise in ferromagnet -
normal metal systems is formulated. Non-collinear magnetization directions of
the ferromagnetic leads, arbitrary junctions and the elastic and inelastic
scattering regimes are considered. The shot noise is governed by a set of
mesoscopic parameters that are expressed in terms of the microscopic details of
the junctions in the circuit. Explicit results in the case of ballistic,
tunnel, and diffusive junctions are evaluated. The shot noise, the current and
the Fano factor are calculated for a double barrier ferromagnet - normal metal
- ferromagnet system. It is demonstrated that the shot noise can have a
non-monotonic behavior as a function of the relative angle between the
magnetizations of the ferromagnetic reservoirs.Comment: 17 pages, 7 figure
Ab-initio prediction of the electronic and optical excitations in polythiophene: isolated chains versus bulk polymer
We calculate the electronic and optical excitations of polythiophene using
the GW approximation for the electronic self-energy, and include excitonic
effects by solving the electron-hole Bethe-Salpeter equation. Two different
situations are studied: excitations on isolated chains and excitations on
chains in crystalline polythiophene. The dielectric tensor for the crystalline
situation is obtained by modeling the polymer chains as polarizable line
objects, with a long-wavelength polarizability tensor obtained from the
ab-initio polarizability function of the isolated chain. With this model
dielectric tensor we construct a screened interaction for the crystalline case,
including both intra- and interchain screening. In the crystalline situation
both the quasi-particle band gap and the exciton binding energies are
drastically reduced in comparison with the isolated chain. However, the optical
gap is hardly affected. We expect this result to be relevant for conjugated
polymers in general.Comment: 15 pages including 4 figures; to appear in Phys. Rev. B, 6/15/200
Imaging Findings Associated with Space-Occupying Edema in Patients with Large Middle Cerebral Artery Infarcts
on behalf of the DUST investigators ABSTRACT BACKGROUND AND PURPOSE: Prominent space-occupying cerebral edema is a devastating complication occurring in some but not all patients with large MCA infarcts. It is unclear why differences in the extent of edema exist. Better knowledge of factors related to prominent edema formation could aid treatment strategies. This study aimed to identify variables associated with the development of prominent edema in patients with large MCA infarcts
Andreev Reflection and Spin Injection into and wave Superconductors
We study the effect of spin injection into and wave superconductors,
with an emphasis on the interplay between boundary and bulk spin transport
properties. The quantities of interest include the amount of non-equilibrium
magnetization (), as well as the induced spin-dependent current () and
boundary voltage (). In general, the Andreev reflection makes each of the
three quantities depend on a different combination of the boundary and bulk
contributions. The situation simplifies either for half-metallic ferromagnets
or in the strong barrier limit, where both and depend solely on the
bulk spin transport/relaxation properties. The implications of our results for
the on-going spin injection experiments in high cuprates are discussed.Comment: 4 pages, REVTEX, 1 figure included; typos correcte
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
An evolution of the IR-Radio correlation at very low flux densities?
In this paper we investigate the radio-MIR correlation at very low flux
densities using extremely deep 1.4 GHz sub-arcsecond angular resolution
MERLIN+VLA observations of a 8'.5 by 8'.5 field centred upon the Hubble Deep
Field North, in conjunction with Spitzer 24micron data. From these results the
MIR-radio correlation is extended to the very faint (~microJy) radio source
population. Tentatively we detect a small deviation from the correlation at the
faintest IR flux densities. We suggest that this small observed change in the
gradient of the correlation is the result of a suppression of the MIR emission
in faint star-forming galaxies. This deviation potentially has significant
implications for using either the MIR or non-thermal radio emission as a
star-formation tracer of very low luminosity galaxies.Comment: Accepted for publication in MNRAS, 14 pages, 9 Figures (7 colour), 2
table
Cross-sections of spallation residues produced in 1.A GeV 208Pb on proton reactions
Spallation residues produced in 1 GeV per nucleon Pb on proton
reactions have been studied using the FRagment Separator facility at GSI.
Isotopic produc- tion cross-sections of elements from Pm to Pb
have been measured down to 0.1 mb with a high accuracy. The recoil kinetic
energies of the produced fragments were also determined. The obtained
cross-sections agree with most of the few existing gamma-spectroscopy data.
Data are compared with different intra nuclear-cascade and evaporation-fission
models. Drastic deviations were found for a standard code used in technical
applications.Comment: 4 pages, 3 figures, accepted for publication in Phys. Rev. Lett.
Revised version May 12, 200
Hadronic production of squark-squark pairs: The electroweak contributions
We compute the electroweak (EW) contributions to squark--squark pair
production processes at the LHC within the framework of the Minimal
Supersymmetric Standard Model (MSSM). Both tree-level EW contributions, of
O(alpha_s alpha + alpha^2), and next-to-leading order (NLO) EW corrections, of
O(alpha_s^2 alpha), are calculated. Depending on the flavor and chirality of
the produced quarks, many interferences between EW-mediated and QCD-mediated
diagrams give non-zero contributions at tree-level and NLO. We discuss the
computational techniques and present an extensive numerical analysis for
inclusive squark--squark production as well as for subsets and single
processes. While the tree-level EW contributions to the integrated cross
sections can reach the 20% level, the NLO EW corrections typically lower the LO
prediction by a few percent.Comment: 36 pages, 18 figure
Parity-sensitive measurements based on ferromagnet/superconductor tunneling junctions
A method to identify the parity of unconventional superconductors is proposed
based on tunneling spectroscopy. For a model of calculation, we adopt a
ferromagnet/superconductor (F/S) junction of which tunneling current is spin
polarized. The tunneling conductance spectra are shown to be quite sensitive to
the direction of the magnetization axis in the ferromagnet only when the
superconductor has odd parity. Therefore, it is possible to distinguish the
parity of the superconductor by measuring the tunneling spectroscopy in F/S
junctions.Comment: 4 pages, 5 figure. To appear in J. Phys. Soc. Jp
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