14,074 research outputs found
Optical evidence for a spin-filter effect in the charge transport of
We have measured the optical reflectivity of
as a function of temperature between 1.5 and 300
and in external magnetic fields up to 7 . The slope at the onset of the
plasma edge feature in increases with decreasing temperature and
increasing field but the plasma edge itself does not exhibit the remarkable
blue shift that is observed in the binary compound . The analysis of
the magnetic field dependence of the low temperature optical conductivity
spectrum confirms the previously observed exponential decrease of the
electrical resistivity upon increasing, field-induced bulk magnetization at
constant temperature. In addition, the individual exponential magnetization
dependences of the plasma frequency and scattering rate are extracted from the
optical data.Comment: submitted to Phys. Rev. Let
Alternative determinism principle for topological analysis of chaos
The topological analysis of chaos based on a knot-theoretic characterization
of unstable periodic orbits has proved a powerful method, however knot theory
can only be applied to three-dimensional systems. Still, the core principles
upon which this approach is built, determinism and continuity, apply in any
dimension. We propose an alternative framework in which these principles are
enforced on triangulated surfaces rather than curves and show that in dimension
three our approach numerically predicts the correct topological entropies for
periodic orbits of the horseshoe map.Comment: Accepted for publication as Rapid Communication in Physical Review
Dispersion relations for stationary light in one-dimensional atomic ensembles
We investigate the dispersion relations for light coupled to one-dimensional
ensembles of atoms with different level schemes. The unifying feature of all
the considered setups is that the forward and backward propagating quantum
fields are coupled by the applied classical drives such that the group velocity
can vanish in an effect known as "stationary light". We derive the dispersion
relations for all the considered schemes, highlighting the important
differences between them. Furthermore, we show that additional control of
stationary light can be obtained by treating atoms as discrete scatterers and
placing them at well defined positions. For the latter purpose, a multi-mode
transfer matrix theory for light is developed
Nonlinear Dynamics of a Bose-Einstein Condensate in a Magnetic Waveguide
We have studied the internal and external dynamics of a Bose-Einstein
condensate in an anharmonic magnetic waveguide. An oscillating condensate
experiences a strong coupling between the center of mass motion and the
internal collective modes. Due to the anharmonicity of the magnetic potential,
not only the center of mass motion shows harmonic frequency generation, but
also the internal dynamics exhibit nonlinear frequency mixing. We describe the
data with a theoretical model to high accuracy. For strong excitations we test
the experimental data for indications of a chaotic behavior.Comment: 4 pages, 4 figure
A polarised infrared flare from Sagittarius A* and the signatures of orbiting plasma hotspots
In this article we summarise and discuss the infrared, radio, and X-ray
emission from the supermassive black hole in the Galactic Centre, SgrA*. We
include new results from near-infrared polarimetric imaging observations
obtained on May 31st, 2006. In that night, a strong flare in Ks band (2.08
microns) reaching top fluxes of ~16 mJy could be observed. This flare was
highly polarised (up to ~40%) and showed clear sub-structure on a time scale of
15 minutes, including a swing in the polarisation angle of about 70 degrees.
For the first time we were able to observe both polarised flux and short-time
variability, with high significance in the same flare event. This result adds
decisive information to the puzzle of the SgrA* activity. The observed
polarisation angle during the flare peak is the same as observed in two events
in 2004 and 2005. Our observations strongly support the dynamical emission
model of a decaying plasma hotspot orbiting SgrA* on a relativistic orbit. The
observed polarisation parameters and their variability with time might allow to
constrain the orientation of accretion disc and spin axis with respect to the
Galaxy.Comment: 9 pages, 8 figures, accepted for publication in MNRA
Ultracold Atoms as a Target: Absolute Scattering Cross-Section Measurements
We report on a new experimental platform for the measurement of absolute
scattering cross-sections. The target atoms are trapped in an optical dipole
trap and are exposed to an incident particle beam. The exponential decay of the
atom number directly yields the absolute total scattering cross-section. The
technique can be applied to any atomic or molecular species that can be
prepared in an optical dipole trap and provides a large variety of possible
scattering scenarios
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