12,736 research outputs found
Optical Weak Link between Two Spatially Separate Bose-Einstein Condensates
Two spatially separate Bose-Einstein condensates were prepared in an optical
double-well potential. A bidirectional coupling between the two condensates was
established by two pairs of Bragg beams which continuously outcoupled atoms in
opposite directions. The atomic currents induced by the optical coupling depend
on the relative phase of the two condensates and on an additional controllable
coupling phase. This was observed through symmetric and antisymmetric
correlations between the two outcoupled atom fluxes. A Josephson optical
coupling of two condensates in a ring geometry is proposed. The continuous
outcoupling method was used to monitor slow relative motions of two elongated
condensates and characterize the trapping potential.Comment: 4 pages, 5 figure
Weibull-type limiting distribution for replicative systems
The Weibull function is widely used to describe skew distributions observed
in nature. However, the origin of this ubiquity is not always obvious to
explain. In the present paper, we consider the well-known Galton-Watson
branching process describing simple replicative systems. The shape of the
resulting distribution, about which little has been known, is found essentially
indistinguishable from the Weibull form in a wide range of the branching
parameter; this can be seen from the exact series expansion for the cumulative
distribution, which takes a universal form. We also find that the branching
process can be mapped into a process of aggregation of clusters. In the
branching and aggregation process, the number of events considered for
branching and aggregation grows cumulatively in time, whereas, for the binomial
distribution, an independent event occurs at each time with a given success
probability.Comment: 6 pages and 5 figure
Polarization Switching Dynamics Governed by Thermodynamic Nucleation Process in Ultrathin Ferroelectric Films
A long standing problem of domain switching process - how domains nucleate -
is examined in ultrathin ferroelectric films. We demonstrate that the large
depolarization fields in ultrathin films could significantly lower the
nucleation energy barrier (U*) to a level comparable to thermal energy (kBT),
resulting in power-law like polarization decay behaviors. The "Landauer's
paradox": U* is thermally insurmountable is not a critical issue in the
polarization switching of ultrathin ferroelectric films. We empirically find a
universal relation between the polarization decay behavior and U*/kBT.Comment: 5 pages, 4 figure
Observation of inhomogeneous domain nucleation in epitaxial Pb(Zr,Ti)O3 capacitors
We investigated domain nucleation process in epitaxial Pb(Zr,Ti)O3 capacitors
under a modified piezoresponse force microscope. We obtained domain evolution
images during polarization switching process and observed that domain
nucleation occurs at particular sites. This inhomogeneous nucleation process
should play an important role in an early stage of switching and under a high
electric field. We found that the number of nuclei is linearly proportional to
log(switching time), suggesting a broad distribution of activation energies for
nucleation. The nucleation sites for a positive bias differ from those for a
negative bias, indicating that most nucleation sites are located at
ferroelectric/electrode interfaces
Three-loop HTL QCD thermodynamics
The hard-thermal-loop perturbation theory (HTLpt) framework is used to
calculate the thermodynamic functions of a quark-gluon plasma to three-loop
order. This is the highest order accessible by finite temperature perturbation
theory applied to a non-Abelian gauge theory before the high-temperature
infrared catastrophe. All ultraviolet divergences are eliminated by
renormalization of the vacuum, the HTL mass parameters, and the strong coupling
constant. After choosing a prescription for the mass parameters, the three-loop
results for the pressure and trace anomaly are found to be in very good
agreement with recent lattice data down to , which are
temperatures accessible by current and forthcoming heavy-ion collision
experiments.Comment: 27 pages, 11 figures; corresponds with published version in JHE
Polarization Relaxation Induced by Depolarization Field in Ultrathin Ferroelectric BaTiO Capacitors
Time-dependent polarization relaxation behaviors induced by a depolarization
field were investigated on high-quality ultrathin
SrRuO/BaTiO/SrRuO capacitors. The values were
determined experimentally from an applied external field to stop the net
polarization relaxation. These values agree with those from the electrostatic
calculations, demonstrating that a large inside the ultrathin
ferroelectric layer could cause severe polarization relaxation. For numerous
ferroelectric devices of capacitor configuration, this effect will set a
stricter size limit than the critical thickness issue
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