14,107 research outputs found
Magnetic properties of PrCu at high pressure
We report a study of the low-temperature high-pressure phase diagram of the
intermetallic compound PrCu, by means of molecular-field calculations and
Cu nuclear-quadrupole-resonance (NQR) measurements under pressure.
The pressure-induced magnetically-ordered phase can be accounted for by
considering the influence of the crystal electric field on the electron
orbitals of the Pr ions and by introducing a pressure-dependent exchange
interaction between the corresponding local magnetic moments. Our experimental
data suggest that the order in the induced antiferromagnetic phase is
incommensurate. The role of magnetic fluctuations both at high and low
pressures is also discussed.Comment: 7 pages, 6 figures, submitted to Eur. Phys. J.
Elastohydrodynamic study of actin filaments using fluorescence microscopy
We probed the bending of actin subject to external forcing and viscous drag.
Single actin filaments were moved perpendicular to their long axis in an
oscillatory way by means of an optically tweezed latex bead attached to one end
of the filaments. Shapes of these polymers were observed by epifluorescence
microscopy. They were found to be in agreement with predictions of semiflexible
polymer theory and slender-body hydrodynamics. A persistence length of m could be extracted.Comment: RevTex, 4 pages, 5 eps figs, submitted to PR
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
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
Controlling the dynamics of an open many-body quantum system with localized dissipation
We experimentally investigate the action of a localized dissipative potential
on a macroscopic matter wave, which we implement by shining an electron beam on
an atomic Bose-Einstein condensate (BEC). We measure the losses induced by the
dissipative potential as a function of the dissipation strength observing a
paradoxical behavior when the strength of the dissipation exceeds a critical
limit: for an increase of the dissipation rate the number of atoms lost from
the BEC becomes lower. We repeat the experiment for different parameters of the
electron beam and we compare our results with a simple theoretical model,
finding excellent agreement. By monitoring the dynamics induced by the
dissipative defect we identify the mechanisms which are responsible for the
observed paradoxical behavior. We finally demonstrate the link between our
dissipative dynamics and the measurement of the density distribution of the BEC
allowing for a generalized definition of the Zeno effect. Due to the high
degree of control on every parameter, our system is a promising candidate for
the engineering of fully governable open quantum systems
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