2,601 research outputs found
Modelling Electron Spin Accumulation in a Metallic Nanoparticle
A model describing spin-polarized current via discrete energy levels of a
metallic nanoparticle, which has strongly asymmetric tunnel contacts to two
ferromagnetic leads, is presented.
In absence of spin-relaxation, the model leads to a spin-accumulation in the
nanoparticle, a difference () between the chemical potentials of
spin-up and spin-down electrons, proportional to the current and the Julliere's
tunnel magnetoresistance. Taking into account an energy dependent
spin-relaxation rate , as a function of bias
voltage () exhibits a crossover from linear to a much weaker dependence,
when equals the spin-polarized current through the
nanoparticle. Assuming that the spin-relaxation takes place via electron-phonon
emission and Elliot-Yafet mechanism, the model leads to a crossover from linear
to dependence. The crossover explains recent measurements of the
saturation of the spin-polarized current with in Aluminum nanoparticles,
and leads to the spin-relaxation rate of in an Aluminum
nanoparticle of diameter , for a transition with an energy difference of
one level spacing.Comment: 37 pages, 7 figure
Water vapor radiometry research and development phase
This report describes the research and development phase for eight dual-channel water vapor radiometers constructed for the Crustal Dynamics Project at the Goddard Space Flight Center, Greenbelt, Maryland, and for the NASA Deep Space Network. These instruments were developed to demonstrate that the variable path delay imposed on microwave radio transmissions by atmospheric water vapor can be calibrated, particularly as this phenomenon affects very long baseline interferometry measurement systems. Water vapor radiometry technology can also be used in systems that involve moist air meteorology and propagation studies
Comments on Drinfeld Realization of Quantum Affine Superalgebra and its Hopf Algebra Structure
By generalizing the Reshetikhin and Semenov-Tian-Shansky construction to
supersymmetric cases, we obtain Drinfeld current realization for quantum affine
superalgebra . We find a simple coproduct for the quantum
current generators and establish the Hopf algebra structure of this super
current algebra.Comment: Some errors and misprints corrected and a remark in section 4
removed. 12 pages, Latex fil
Transfer matrix eigenvalues of the anisotropic multiparametric U model
A multiparametric extension of the anisotropic U model is discussed which
maintains integrability. The R-matrix solving the Yang-Baxter equation is
obtained through a twisting construction applied to the underlying Uq(sl(2|1))
superalgebraic structure which introduces the additional free parameters that
arise in the model. Three forms of Bethe ansatz solution for the transfer
matrix eigenvalues are given which we show to be equivalent.Comment: 26 pages, no figures, LaTe
Jacobson generators of the quantum superalgebra and Fock representations
As an alternative to Chevalley generators, we introduce Jacobson generators
for the quantum superalgebra . The expressions of all
Cartan-Weyl elements of in terms of these Jacobson generators
become very simple. We determine and prove certain triple relations between the
Jacobson generators, necessary for a complete set of supercommutation relations
between the Cartan-Weyl elements. Fock representations are defined, and a
substantial part of this paper is devoted to the computation of the action of
Jacobson generators on basis vectors of these Fock spaces. It is also
determined when these Fock representations are unitary. Finally, Dyson and
Holstein-Primakoff realizations are given, not only for the Jacobson
generators, but for all Cartan-Weyl elements of .Comment: 27 pages, LaTeX; to be published in J. Math. Phy
Quantum superalgebras at roots of unity and non-abelian symmetries of integrable models
We consider integrable vertex models whose Boltzmann weights (R-matrices) are
trigonometric solutions to the graded Yang-Baxter equation. As is well known
the latter can be generically constructed from quantum affine superalgebras
. These algebras do not form a symmetry algebra of the model for
generic values of the deformation parameter when periodic boundary
conditions are imposed. If is evaluated at a root of unity we demonstrate
that in certain commensurate sectors one can construct non-abelian subalgebras
which are translation invariant and supercommute with the transfer matrix and
therefore with all charges of the model. In the line of argument we introduce
the restricted quantum superalgebra and investigate its
root of unity limit. We prove several new formulas involving supercommutators
of arbitrary powers of the Chevalley-Serre generators and derive higher order
quantum Serre relations as well as an analogue of Lustzig's quantum Frobenius
theorem for superalgebras.Comment: 31 pages, tcilatex (minor typos corrected
Level-one Highest Weight Representation of and Bosonization of the Multi-component Super t-J Model
We study the level-one irreducible highest weight representations of the
quantum affine superalgebra , and calculate their
characters and supercharacters. We obtain bosonized q-vertex operators acting
on the irreducible -modules and derive the exchange
relations satisfied by the vertex operators. We give the bosonization of the
multi-component super model by using the bosonized vertex operators.Comment: LaTex file 21 page
Ba3Ga3N5 - A Novel Host Lattice for Eu2+ - Doped Luminescent Materials with Unexpected Nitridogallate Substructure
The alkaline earth nitridogallate Ba3Ga3N5 was synthesized from the elements in a sodium flux at 760°C utilizing weld shut tantalum ampules. The crystal structure was solved and refined on the basis of single-crystal X-ray diffraction data. Ba3Ga3N5 (space group C2/c (No. 15), a = 16.801(3), b = 8.3301(2), c = 11.623(2) Å, β = 109.92 (3)°, Z = 8) contains a hitherto unknown structural motif in nitridogallates, namely, infinite strands made up of GaN4 tetrahedra, each sharing two edges and at least one corner with neighboring GaN4 units. There are three Ba2+ sites with coordination numbers six or eight, respectively, and one Ba2+ position exhibiting a low coordination number 4 corresponding to a distorted tetrahedron. Eu2+ - doped samples show red luminescence when excited by UV irradiation at room temperature. Luminescence investigations revealed a maximum emission intensity at 638 nm (FWHM =2123 cm−1). Ba3Ga3N5 is the first nitridogallate for which parity allowed broadband emission due to Eu2+ - doping has been found. The electronic structure of both Ba3Ga3N5 as well as isoelectronic but not isostructural Sr3Ga3N5 was investigated by DFT methods. The calculations revealed a band gap of 1.53 eV for Sr3Ga3N5 and 1.46 eV for Ba3Ga3N5
Drinfel'd Realization of Quantum Affine Superalgebra
We obtain Drinfel'd's realization of quantum affine superalgebra
based on the super version of RS construction method and
Gauss decomposition
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