853 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
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
Heat Capacity of Mesoscopic Superconducting Disks
We study the heat capacity of isolated giant vortex states, which are good
angular momentum () states, in a mesoscopic superconducting disk using the
Ginzburg-Landau (GL) theory. At small magnetic fields the =0 state
qualitatively behaves like the bulk sample characterized by a discontinuity in
heat capacity at . As the field is increased the discontinuity slowly
turns into a continuous change which is a finite size effect. The higher
states show a continuous change in heat capacity at at all fields. We
also show that for these higher states, the behavior of the peak position
with change in field is related to the paramagnetic Meissner effect
(irreversible) and can lead to an unambiguous observation of positive
magnetization in mesoscopic superconductors.Comment: Final versio
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
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
Order parameter and vortices in the superconducting Q-phase of CeCoIn5
Recently, it has been reported that the low-temperature high-magnetic field
phase in CeCoIn5 (Q-phase), has spin-density wave (SDW) order that only exists
within this phase. This indicates that the SDW order is the result of the
development of pair density wave (PDW) order in the superconducting phase that
coexists with d-wave superconductivity. Here we develop a phenomenological
theory for these coexisting orders. This provides selection rules for the PDW
order and further shows that the detailed structure of this order is highly
constrained. We then apply our theory to the the vortex phase. This reveals
vortex phases in which the d-wave vortex cores exhibit charge density wave
(CDW) order and further reveals that the SDW order provides a unique probe of
the vortex phase.Comment: 4 pages, 2 figures, 1 tabl
Determination of the critical current density in the d-wave superconductor YBCO under applied magnetic fields by nodal tunneling
We have studied nodal tunneling into YBa2Cu3O7-x (YBCO) films under magnetic
fields. The films' orientation was such that the CuO2 planes were perpendicular
to the surface with the a and b axis at 450 form the normal. The magnetic field
was applied parallel to the surface and perpendicular to the CuO2 planes. The
Zero Bias Conductance Peak (ZBCP) characteristic of nodal tunneling splits
under the effect of surface currents produced by the applied fields. Measuring
this splitting under different field conditions, zero field cooled and field
cooled, reveals that these currents have different origins. By comparing the
field cooled ZBCP splitting to that taken in decreasing fields we deduce a
value of the Bean critical current superfluid velocity, and calculate a Bean
critical current density of up to 3*10^7 A/cm2 at low temperatures. This
tunneling method for the determination of critical currents under magnetic
fields has serious advantages over the conventional one, as it avoids having to
make high current contacts to the sample.Comment: 8 pages, 2 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
Stability of the vortex lattice in D-wave superconductors
Use is made of Onsager's hydrodynamic equation to derive the vibration
spectrum of the vortex lattice in d-wave superconductor. In particular the
rhombic lattice (i.e. the tilted square lattice) is found to be
stable for . Here denotes the critical field at which
the vortex lattice transition takes place.Comment: 7 pages, Revte
Superconductivity in domains with corners
We study the two-dimensional Ginzburg-Landau functional in a domain with
corners for exterior magnetic field strengths near the critical field where the
transition from the superconducting to the normal state occurs. We discuss and
clarify the definition of this field and obtain a complete asymptotic expansion
for it in the large regime. Furthermore, we discuss nucleation of
superconductivity at the boundary
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