229 research outputs found
Symbiotic gap and semi-gap solitons in Bose-Einstein condensates
Using the variational approximation and numerical simulations, we study
one-dimensional gap solitons in a binary Bose-Einstein condensate trapped in an
optical-lattice potential. We consider the case of inter-species repulsion,
while the intra-species interaction may be either repulsive or attractive.
Several types of gap solitons are found: symmetric or asymmetric; unsplit or
split, if centers of the components coincide or separate; intra-gap (with both
chemical potentials falling into a single bandgap) or inter-gap, otherwise. In
the case of the intra-species attraction, a smooth transition takes place
between solitons in the semi-infinite gap, the ones in the first finite
bandgap, and semi-gap solitons (with one component in a bandgap and the other
in the semi-infinite gap).Comment: 5 pages, 9 figure
Scattering and Trapping of Nonlinear Schroedinger Solitons in External Potentials
Soliton motion in some external potentials is studied using the nonlinear
Schr\"odinger equation. Solitons are scattered by a potential wall. Solitons
propagate almost freely or are trapped in a periodic potential. The critical
kinetic energy for reflection and trapping is evaluated approximately with a
variational method.Comment: 9 pages, 7 figure
Second magnetization peak in flux lattices: the decoupling scenario
The second peak phenomena of flux lattices in layered superconductors is
described in terms of a disorder induced layer decoupling transition. For weak
disorder the tilt mudulus undergoes an apparent discontinuity which leads to an
enhanced critical current and reduced domain size in the decoupled phase. The
Josephson plasma frequency is reduced by decoupling and by Josephson glass
pinning; in the liquid phase it varies as 1/[BT(T+T_0)] where T is temperature,
B is field and T_0 is the disorder dependent temperature of the multicritical
point.Comment: 5 pages, 1 eps figure, Revtex. Minor changes, new reference
Matter-wave vortices in cigar-shaped and toroidal waveguides
We study vortical states in a Bose-Einstein condensate (BEC) filling a
cigar-shaped trap. An effective one-dimensional (1D) nonpolynomial Schroedinger
equation (NPSE) is derived in this setting, for the models with both repulsive
and attractive inter-atomic interactions. Analytical formulas for the density
profiles are obtained from the NPSE in the case of self-repulsion within the
Thomas-Fermi approximation, and in the case of the self-attraction as exact
solutions (bright solitons). A crucially important ingredient of the analysis
is the comparison of these predictions with direct numerical solutions for the
vortex states in the underlying 3D Gross-Pitaevskii equation (GPE). The
comparison demonstrates that the NPSE provides for a very accurate
approximation, in all the cases, including the prediction of the stability of
the bright solitons and collapse threshold for them. In addition to the
straight cigar-shaped trap, we also consider a torus-shaped configuration. In
that case, we find a threshold for the transition from the axially uniform
state, with the transverse intrinsic vorticity, to a symmetry-breaking pattern,
due to the instability in the self-attractive BEC filling the circular trap.Comment: 6 pages, Physical Review A, in pres
Stability of the Bragg glass phase in a layered geometry
We study the stability of the dislocation-free Bragg glass phase in a layered
geometry consisting of coupled parallel planes of d=1+1 vortex lines lying
within each plane, in the presence of impurity disorder. Using renormalization
group, replica variational calculations and physical arguments we show that at
temperatures the 3D Bragg glass phase is always stable for weak
disorder. It undergoes a weakly first order transition into a decoupled 2D
vortex glass upon increase of disorder.Comment: RevTeX. Submitted to EP
Field-induced transition between magnetically disordered and ordered phases in underdoped La(2-x)SrxCuO4
We report the observation of a magnetic-field-induced transition between
magnetically disordered and ordered phases in slightly under-doped
La(2-x)SrxCuO4 with x=0.144. Static incommensurate spin-density-wave order is
induced above a critical field of about 3 T, as measured by elastic neutron
scattering. Our results allow us to constrain the location of a quantum
critical point on the phase diagram.Comment: 10 pages, 2 figures; discussion on the location of a quantum critical
point is revise
Stabilization and destabilization of second-order solitons against perturbations in the nonlinear Schr\"{o}dinger equation
We consider splitting and stabilization of second-order solitons (2-soliton
breathers) in a model based on the nonlinear Schr\"{o}dinger equation (NLSE),
which includes a small quintic term, and weak resonant nonlinearity management
(NLM), i.e., time-periodic modulation of the cubic coefficient, at the
frequency close to that of shape oscillations of the 2-soliton. The model
applies to the light propagation in media with cubic-quintic optical
nonlinearities and periodic alternation of linear loss and gain, and to BEC,
with the self-focusing quintic term accounting for the weak deviation of the
dynamics from one-dimensionality, while the NLM can be induced by means of the
Feshbach resonance. We propose an explanation to the effect of the resonant
splitting of the 2-soliton under the action of the NLM. Then, using systematic
simulations and an analytical approach, we conclude that the weak quintic
nonlinearity with the self-focusing sign stabilizes the 2-soliton, while the
self-defocusing quintic nonlinearity accelerates its splitting. It is also
shown that the quintic term with the self-defocusing/focusing sign makes the
resonant response of the 2-soliton to the NLM essentially broader, in terms of
the frequency.Comment: 16 pages, 6 figure
From X-Ray Telescopes to Neutron Scattering: Using Wolter Mirrors to Focus a Neutron Beam
No abstract availabl
Reflection of Channel-Guided Solitons at Junctions in Two-Dimensional Nonlinear Schroedinger Equation
Solitons confined in channels are studied in the two-dimensional nonlinear
Schr\"odinger equation. We study the dynamics of two channel-guided solitons
near the junction where two channels are merged. The two solitons merge into
one soliton, when there is no phase shift. If a phase difference is given to
the two solitons, the Josephson oscillation is induced. The Josephson
oscillation is amplified near the junction. The two solitons are reflected when
the initial velocity is below a critical value.Comment: 3 pages, 2 figure
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