6,094 research outputs found
A note on the integrability of non-Hermitian extensions of Calogero-Moser-Sutherland models
We consider non-Hermitian but PT-symmetric extensions of Calogero models,
which have been proposed by Basu-Mallick and Kundu for two types of Lie
algebras. We address the question of whether these extensions are meaningful
for all remaining Lie algebras (Coxeter groups) and if in addition one may
extend the models beyond the rational case to trigonometric, hyperbolic and
elliptic models. We find that all these new models remain integrable, albeit
for the non-rational potentials one requires additional terms in the extension
in order to compensate for the breaking of integrability.Comment: 10 pages, Late
Quantum interference from remotely trapped ions
We observe quantum interference of photons emitted by two continuously
laser-excited single ions, independently trapped in distinct vacuum vessels.
High contrast two-photon interference is observed in two experiments with
different ion species, calcium and barium. Our experimental findings are
quantitatively reproduced by Bloch equation calculations. In particular, we
show that the coherence of the individual resonance fluorescence light field is
determined from the observed interference
Suppression of Magnetic Order by Pressure in BaFe2As2
We performed the dc resistivity and the ZF 75As-NMR measurement of BaFe2As2
under high pressure. The T-P phase diagram of BaFe2As2 determined from
resistivity anomalies and the ZF 75As-NMR clearly revealed that the SDW anomaly
is quite robust against P.Comment: 2 pages, 2 figure
Magnetic properties of iron pnictides from spin-spiral calculations
The wave-vector (q) and doping dependences of the magnetic energy, iron
moment, and effective exchange interactions in LaFeAsO, BaFe2As2, and SrFe2As2\
are studied by self-consistent LSDA calculations for co-planar spin spirals.
For the undoped compounds, the calculated total energy, E(q), reaches its
minimum at q corresponding to stripe anti-ferromagnetic order. In LaFeAsO, this
minimum becomes flat already at low levels of electron-doping and shifts to an
incommensurate q at delta=0.2, where delta is the number of additional
electrons (delta>0) or holes (delta<0) per Fe. In BaFe2As2 and SrFe2As2, stripe
order remains stable for hole doping down to delta=-0.3. Under electron doping,
on the other hand, the E(q) minimum shifts to incommensurate q already at
delta=0.1.Comment: 4 pages, 2 figures, International Conference on Magnetism, Karlsruhe,
July 26 - 31, 200
An X-ray Study of Two B+B Binaries: AH Cep and CW Cep
AH Cep and CW Cep are both early B-type binaries with short orbital periods
of 1.8~d and 2.7~d, respectively. All four components are B0.5V types. The
binaries are also double-lined spectroscopic and eclipsing. Consequently,
solutions for orbital and stellar parameters make the pair of binaries ideal
targets for a study of the colliding winds between two B~stars. {\em Chandra}
ACIS-I observations were obtained to determine X-ray luminosities. AH~Cep was
detected with an unabsorbed X-ray luminosity at a 90\% confidence interval of
erg s, or ,
relative to the combined Bolometric luminosities of the two components. While
formally consistent with expectations for embedded wind shocks, or binary wind
collision, the near-twin system of CW~Cep was a surprising non-detection. For
CW~Cep, an upper limit was determined with , again
for the combined components. One difference between these two systems is that
AH~Cep is part of a multiple system. The X-rays from AH~Cep may not arise from
standard wind shocks nor wind collision, but perhaps instead from magnetism in
any one of the four components of the system. The possibility could be tested
by searching for cyclic X-ray variability in AH~Cep on the short orbital period
of the inner B~stars.Comment: Astrophysical Journal, accepte
Ab initio lattice dynamics simulations and inelastic neutron scattering spectra for studying phonons in BaFe2As2: Effect of structural phase transition, structural relaxation and magnetic ordering
We have performed extensive ab initio calculations to investigate phonon
dynamics and their possible role in superconductivity in BaFe2As2 and related
systems. The calculations are compared to inelastic neutron scattering data
that offer improved resolution over published data [Mittal et al., PRB 78
104514 (2008)], in particular at low frequencies. Effects of structural phase
transition and full/partial structural relaxation, with and without magnetic
ordering, on the calculated vibrational density of states are reported. Phonons
are best reproduced using either the relaxed magnetic structures or the
experimental cell. Several phonon branches are affected by the subtle
structural changes associated with the transition from the tetragonal to the
orthorhombic phase. Effects of phonon induced distortions on the electronic and
spin structure have been investigated. It is found that for some vibrational
modes, there is a significant change of the electronic distribution and spin
populations around the Fermi level. A peak at 20 meV in the experimental data
falls into the pseudo-gap region of the calculation. This was also the case
reported in our recent work combined with an empirical parametric calculation
[Mittal et al., PRB 78 104514 (2008)]. The combined evidence for the coupling
of electronic and spin degrees of freedom with phonons is relevant to the
current interest in superconductivity in BaFe2As2 and related systems
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