2,102 research outputs found
Ferromagnetic coupling and magnetic anisotropy in molecular Ni(II) squares
We investigated the magnetic properties of two isostructural Ni(II) metal
complexes [Ni4Lb8] and [Ni4Lc8]. In each molecule the four Ni(II) centers form
almost perfect regular squares. Magnetic coupling and anisotropy of single
crystals were examined by magnetization measurements and in particular by
high-field torque magnetometry at low temperatures. The data were analyzed in
terms of an effective spin Hamiltonian appropriate for Ni(II) centers. For both
compounds, we found a weak intramolecular ferromagnetic coupling of the four
Ni(II) spins and sizable single-ion anisotropies of the easy-axis type. The
coupling strengths are roughly identical for both compounds, whereas the
zero-field-splitting parameters are significantly different. Possible reasons
for this observation are discussed.Comment: 7 pages, 7 figure
Collective resonance modes of Josephson vortices in sandwiched stack of BiSrCaCuO intrinsic Josephson junctions
We observed splitting of the low-bias vortex-flow branch in a
dense-Josephson-vortex state into multiple sub-branches in current-voltage
characteristics of intrinsic Josephson junctions (IJJs) of
BiSrCaCuO single crystals in the long-junction limit.
Each sub-branch corresponds to a plasma mode in serially coupled Josephson
junctions. Splitting into low-bias linear sub-branches with a spread in the
slopes and the inter-sub-branch mode-switching character are in good
quantitative agreement with the prediction of the weak but finite
inter-junction capacitive-coupling model incorporated with the inductive
coupling. This suggests the importance of the role of the capacitive coupling
in accurately describing the vortex dynamics in serially stacked IJJs.Comment: 4 pages, 3 figures, 1 tabl
Algebraic approach to quantum field theory on a class of noncommutative curved spacetimes
In this article we study the quantization of a free real scalar field on a
class of noncommutative manifolds, obtained via formal deformation quantization
using triangular Drinfel'd twists. We construct deformed quadratic action
functionals and compute the corresponding equation of motion operators. The
Green's operators and the fundamental solution of the deformed equation of
motion are obtained in terms of formal power series. It is shown that, using
the deformed fundamental solution, we can define deformed *-algebras of field
observables, which in general depend on the spacetime deformation parameter.
This dependence is absent in the special case of Killing deformations, which
include in particular the Moyal-Weyl deformation of the Minkowski spacetime.Comment: LaTeX 14 pages, no figures, svjour3.cls style; v2: clarifications and
references added, compatible with published versio
Exchange-coupling constants, spin density map, and Q dependence of the inelastic neutron scattering intensity in single-molecule magnets
The Q dependence of the inelastic neutron scattering (INS) intensity of
transitions within the ground-state spin multiplet of single-molecule magnets
(SMMs) is considered. For these transitions, the Q dependence is related to the
spin density map in the ground state, which in turn is governed by the
Heisenberg exchange interactions in the cluster. This provides the possibility
to infer the exchange-coupling constants from the Q dependence of the INS
transitions within the spin ground state. The potential of this strategy is
explored for the M = +-10 -> +- 9 transition within the S = 10 multiplet of the
molecule Mn12 as an example. The Q dependence is calculated for powder as well
as single-crystal Mn12 samples for various exchange-coupling situations
discussed in the literature. The results are compared to literature data on a
powder sample of Mn12 and to measurements on an oriented array of about 500
single-crystals of Mn12. The calculated Q dependence exhibits significant
variation with the exchange-coupling constants, in particular for a
single-crystal sample, but the experimental findings did not permit an
unambiguous determination. However, although challenging, suitable experiments
are within the reach of today's instruments.Comment: 11 pages, 6 figures, REVTEX4, to appear in PR
Quantum Phase Interference and Neel-Vector Tunneling in Antiferromagnetic Molecular Wheels
The antiferromagnetic molecular wheel Fe18 of eighteen exchange-coupled
Fe(III) ions has been studied by measurements of the magnetic torque, the
magnetization, and the inelastic neutron scattering spectra. The combined data
show that the low-temperature magnetism of Fe18 is very accurately described by
the Neel-vector tunneling (NVT) scenario, as unfolded by semiclassical theory.
In addition, the magnetic torque as a function of applied field exhibits
oscillations that reflect the oscillations in the NVT tunnel splitting with
field due to quantum phase interference.Comment: 5 pages, 4 figures, REVTEX4, to appear in PR
A population study of gaseous exoplanets
We present here the analysis of 30 gaseous extrasolar planets, with
temperatures between 600 and 2400 K and radii between 0.35 and 1.9
. The quality of the HST/WFC3 spatially scanned data combined
with our specialized analysis tools allow us to study the largest and most
self-consistent sample of exoplanetary transmission spectra to date and examine
the collective behavior of warm and hot gaseous planets rather than isolated
case-studies. We define a new metric, the Atmospheric Detectability Index (ADI)
to evaluate the statistical significance of an atmospheric detection and find
statistically significant atmospheres around 16 planets out of the 30 analysed.
For most of the Jupiters in our sample, we find the detectability of their
atmospheres to be dependent on the planetary radius but not on the planetary
mass. This indicates that planetary gravity plays a secondary role in the state
of gaseous planetary atmospheres. We detect the presence of water vapour in all
of the statistically detectable atmospheres, and we cannot rule out its
presence in the atmospheres of the others. In addition, TiO and/or VO
signatures are detected with 4 confidence in WASP-76 b, and they are
most likely present in WASP-121 b. We find no correlation between expected
signal-to-noise and atmospheric detectability for most targets. This has
important implications for future large-scale surveys.Comment: 14 pages, 12 figures, 3 tables, published in A
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