17,152 research outputs found
Anisotropic magnetic behavior of GdBa_2Cu_3O_{6+y} single crystals
Magnetic properties of high-quality Al-free nonsuperconducting
GdBa_2Cu_3O_{6+y} single crystals grown by flux method have been studied. The
magnetic anisotropy below the N\'eel temperature T_N~2.3K corresponds to the
direction of Gd^{3+} magnetic moments along the tetragonal c-axis. At T < T_N
clear indications of spin-flop transitions for H||c have been observed on
magnetization curves at H_{sf}~10kOe. Magnetic phase diagrams have been
obtained for H||c as well as for H||ab. A pronounced anisotropy in the magnetic
susceptibility (unexpected for Gd-based compounds) has been found above T_N.Comment: 2 pages, 3 figures; LT23 (Aug. 2002; Hiroshima), accepted to Physica
Deformations of modules of differential forms
We study non-trivial deformations of the natural action of the Lie algebra
on the space of differential forms on . We calculate abstractions for integrability of infinitesimal
multi-parameter deformations and determine the commutative associative algebra
corresponding to the miniversal deformation in the sense of \cite{ff}.Comment: Published by JNMP at http://www.sm.luth.se/math/JNM
Non-additivity of optical and Casimir-Polder potentials
An atom irradiated by an off-resonant laser field near a surface is expected
to experience the sum of two fundamental potentials, the optical potential of
the laser field and the Casimir--Polder potential of the surface. Here, we
report a new non-additive potential, namely the laser-induced Casimir--Polder
potential, which arises from a correlated coupling of the atom with both the
laser and the quantum vacuum. We apply this result to an experimentally
realizable scenario of an atomic mirror with an evanescent laser beam leaking
out of a surface. We show that the non-additive term is significant for
realistic experimental parameters, transforming potential barriers into
potential wells, which can be used to trap atoms near surfaces.Comment: 5 pages, 3 figure
Constraints on the relativistic mean field of -isobar in nuclear matter
The effects of the presence of -isobars in nuclear matter are studied
in the framework of relativistic mean-field theory. The existence of stable
nuclei at saturation density imposes constraints on the -isobar
self-energy and thereby on the mean-field coupling constants of the scalar and
vector mesons with -isobars. The range of possible values for the
scalar and vector coupling constants of -isobars with respect to the
nucleon coupling is investigated and compared to recent predictions of QCD
sum-rule calculations.Comment: 8 pages, Latex using Elsevier style, 2 PS figures, minor changes in
revised versio
Intrinsic defects in silicon carbide LED as a perspective room temperature single photon source in near infrared
Generation of single photons has been demonstrated in several systems.
However, none of them satisfies all the conditions, e.g. room temperature
functionality, telecom wavelength operation, high efficiency, as required for
practical applications. Here, we report the fabrication of light emitting
diodes (LEDs) based on intrinsic defects in silicon carbide (SiC). To fabricate
our devices we used a standard semiconductor manufacturing technology in
combination with high-energy electron irradiation. The room temperature
electroluminescence (EL) of our LEDs reveals two strong emission bands in
visible and near infrared (NIR), associated with two different intrinsic
defects. As these defects can potentially be generated at a low or even single
defect level, our approach can be used to realize electrically driven single
photon source for quantum telecommunication and information processing
A reason for fusion rules to be even
We show that certain tensor product multiplicities in semisimple braided
sovereign tensor categories must be even. The quantity governing this behavior
is the Frobenius-Schur indicator. The result applies in particular to the
representation categories of large classes of groups, Lie algebras, Hopf
algebras and vertex algebras.Comment: 6 pages, LaTe
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