7,009 research outputs found
Ground State and Tkachenko Modes of a Rapidly Rotating Bose-Einstein Condensate in the Lowest Landau Level State
The Letter considers the ground state and the Tkachenko modes for a rapidly
rotating Bose-Einstein condensate (BEC), when its macroscopic wave function is
a coherent superposition of states analogous to the lowest Landau levels of a
charge in a magnetic field. As well as in type II superconductors close to the
critical magnetic field , this corresponds to a periodic vortex
lattice. The exact value of the shear elastic modulus of the vortex lattice,
which was known from the old works on type II superconductors, essentially
exceeds the values calculated recently for BEC. This is important for
comparison with observation of the Tkachenko mode in the rapidly rotating BEC.Comment: 5 pages, 1 figure; discussion edited, references added, numerical
factors and typos correcte
Mechanical probing of liquid foam aging
We present experimental results on the Stokes experiment performed in a 3D
dry liquid foam. The system is used as a rheometric tool : from the force
exerted on a 1cm glass bead, plunged at controlled velocity in the foam in a
quasi static regime, local foam properties are probed around the sphere. With
this original and simple technique, we show the possibility of measuring the
foam shear modulus, the gravity drainage rate and the evolution of the bubble
size during coarsening
FFLO states and quantum oscillations in mesoscopic superconductors and superfluid ultracold Fermi gases
We have studied the distinctive features of the
Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) instability and phase transitions in
two--dimensional (2D) mesoscopic superconductors placed in magnetic field of
arbitrary orientation and rotating superfluid Fermi gases with imbalanced state
populations. Using a generalized version of the phenomenological
Ginzburg-Landau theory we have shown that the FFLO states are strongly modified
by the effect of the trapping potential confining the condensate. The
phenomenon of the inhomogeneous state formation is determined by the interplay
of three length scales: (i) length scale of the FFLO instability; (ii) 2D
system size; (iii) length scale associated with the orbital effect caused
either by the Fermi condensate rotation or magnetic field component applied
perpendicular to the superconducting disc. We have studied this interplay and
resulting quantum oscillation effects in both superconducting and superfluid
finite -- size systems with FFLO instability and described the hallmarks of the
FFLO phenomenon in a restricted geometry. The finite size of the system is
shown to affect strongly the conditions of the observability of switching
between the states with different vorticities.Comment: 11 pages, 5 figures, Submitted to PR
Anisotropy and effective dimensionality crossover of the fluctuation conductivity of hybrid superconductor/ferromagnet structures
We study the fluctuation conductivity of a superconducting film, which is
placed to perpendicular non-uniform magnetic field with the amplitude
induced by the ferromagnet with domain structure. The conductivity tensor is
shown to be essentially anisotropic. The magnitude of this anisotropy is
governed by the temperature and the typical width of magnetic domains . For
the difference between diagonal fluctuation
conductivity components along the domain walls and
across them has the order of . In the
opposite case for the fluctuation conductivity tensor reveals
effective dimensionality crossover from standard two-dimensional
behavior well above the critical temperature to the one-dimensional
one close to for or to the
dependence for . In the intermediate case
for a fixed temperature shift from the dependence
is shown to have a minimum at
while is a monotonically increasing function.Comment: 11 pages, 8 figure
Oscillations of magnetization and conductivity in anisotropic Fulde-Ferrell-Larkin-Ovchinnikov superconductors
We derive the fluctuational magnetization and the paraconductivity of
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconductors in their normal state.
The FFLO superconducting fluctuations induce oscillations of the magnetization
between diamagnetism and unusual paramagnetism which originates from the
competition between paramagnetic and orbital effects. We also predict a strong
anisotropy of the paraconductivity when the FFLO transition is approached in
contrast with the case of a uniform BCS state. Finally building a
Ginzburg-Levanyuk argument, we demonstrate that these fluctuation effects can
be safely treated within the Gaussian approximation since the critical
fluctuations are proeminent only within an experimentally inaccessible
temperature interval
Blow-up of the hyperbolic Burgers equation
The memory effects on microscopic kinetic systems have been sometimes
modelled by means of the introduction of second order time derivatives in the
macroscopic hydrodynamic equations. One prototypical example is the hyperbolic
modification of the Burgers equation, that has been introduced to clarify the
interplay of hyperbolicity and nonlinear hydrodynamic evolution. Previous
studies suggested the finite time blow-up of this equation, and here we present
a rigorous proof of this fact
A homomorphism between link and XXZ modules over the periodic Temperley-Lieb algebra
We study finite loop models on a lattice wrapped around a cylinder. A section
of the cylinder has N sites. We use a family of link modules over the periodic
Temperley-Lieb algebra EPTL_N(\beta, \alpha) introduced by Martin and Saleur,
and Graham and Lehrer. These are labeled by the numbers of sites N and of
defects d, and extend the standard modules of the original Temperley-Lieb
algebra. Beside the defining parameters \beta=u^2+u^{-2} with u=e^{i\lambda/2}
(weight of contractible loops) and \alpha (weight of non-contractible loops),
this family also depends on a twist parameter v that keeps track of how the
defects wind around the cylinder. The transfer matrix T_N(\lambda, \nu) depends
on the anisotropy \nu and the spectral parameter \lambda that fixes the model.
(The thermodynamic limit of T_N is believed to describe a conformal field
theory of central charge c=1-6\lambda^2/(\pi(\lambda-\pi)).)
The family of periodic XXZ Hamiltonians is extended to depend on this new
parameter v and the relationship between this family and the loop models is
established. The Gram determinant for the natural bilinear form on these link
modules is shown to factorize in terms of an intertwiner i_N^d between these
link representations and the eigenspaces of S^z of the XXZ models. This map is
shown to be an isomorphism for generic values of u and v and the critical
curves in the plane of these parameters for which i_N^d fails to be an
isomorphism are given.Comment: Replacement of "The Gram matrix as a connection between periodic loop
models and XXZ Hamiltonians", 31 page
Josephson junctions in thin and narrow rectangular superconducting strips
I consider a Josephson junction crossing the middle of a thin rectangular
superconducting strip of length L and width W subjected to a perpendicular
magnetic induction B. I calculate the spatial dependence of the gauge-invariant
phase difference across the junction and the resulting B dependence of the
critical current Ic(B).Comment: 4 pages, 6 figures, revised following referee's comment
Experimental study of granular surface flows via a fast camera: a continuous description
Depth averaged conservation equations are written for granular surface flows.
Their application to the study of steady surface flows in a rotating drum
allows to find experimentally the constitutive relations needed to close these
equations from measurements of the velocity profile in the flowing layer at the
center of the drum and from the flowing layer thickness and the static/flowing
boundary profiles. The velocity varies linearly with depth, with a gradient
independent of both the flowing layer thickness and the static/flowing boundary
local slope. The first two closure relations relating the flow rate and the
momentum flux to the flowing layer thickness and the slope are then deduced.
Measurements of the profile of the flowing layer thickness and the
static/flowing boundary in the whole drum explicitly give the last relation
concerning the force acting on the flowing layer. Finally, these closure
relations are compared to existing continuous models of surface flows.Comment: 20 pages, 11 figures, submitted to Phys. FLuid
- …