602 research outputs found
New High Field State of Flux Line Lattice in Unconventional Superconductor CeCoIn_5
Ultrasound velocity measurements of the unconventional superconductor
CeCoIn_5 with extremely large Pauli paramagnetic susceptibility reveal an
unusual structural transformation of the flux line lattice (FLL) in the
vicinity of the upper critical field. The transition field coincides with that
at which heat capacity measurements reveal a second order phase transition. The
lowering of the sound velocity at the transition is consistent with the
collapse of the FLL tilt modulus and a crossover to quasi two-dimensional FLL
pinning. These results provide a strong evidence that the high field state is
the Fulde-Ferrel-Larkin-Ovchinikov phase, in which the order parameter is
spatially modulated and has planar nodes aligned perpendicular to the vortices.Comment: 5 pages, 4 figure
Superconducting fluctuations at low temperature
The effect of fluctuations on the transport and thermodynamic properties of
two-dimensional superconductors in a magnetic field is studied at low
temperature. The fluctuation conductivity is calculated in the framework of the
perturbation theory with the help of usual diagram technique. It is shown that
in the dirty case the Aslamazov-Larkin, Maki-Thomson and Density of States
contributions are of the same order. At extremely low temperature, the total
fluctuation correction to the normal conductivity is negative in the dirty
limit and depends on the external magnetic field logarithmically. In the
non-local clean limit, the Aslamazov-Larkin contribution to conductivity is
evaluated with the aid of the Helfand-Werthamer theory. The longitudinal and
Hall conductivities are found. The fluctuating magnetization is calculated in
the one-loop and two-loop approximations.Comment: 12 pages, 4 figures, submitted to Phys. Rev.
Temperature dependence of the upper critical field of an anisotropic singlet superconductivity in a square lattice tight-binding model in parallel magnetic fields
Upper critical field parallel to the conducting layer is studied in
anisotropic type-II superconductors on square lattices. We assume enough
separation of the adjacent layers, for which the orbital pair-breaking effect
is suppressed for exactly aligned parallel magnetic field. In particular, we
examine the temperature dependence of the critical field H_c(T) of the
superconductivity including the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO or LOFF)
state, in which the Cooper pairs have non-zero center-of-mass momentum q. In
the system with the cylindrically symmetric Fermi-surface, it is known that
H_c(T) of the d-wave FFLO state exhibits a kink at a low temperature due to a
change of the direction of q in contrast to observations in organic
superconductors. It is shown that the kink disappears when the Fermi-surface is
anisotropic to some extent, since the direction of q is locked in an optimum
direction independent of the temperature.Comment: 5 pages, 5 figures, revtex.sty, submitted to J.Phys.Soc.Jp
Metals in high magnetic field: a new universality class of Fermi liquids
Parquet equations, describing the competition between superconducting and
density-wave instabilities, are solved for a three-dimensional isotropic metal
in a high magnetic field when only the lowest Landau level is filled. In the
case of a repulsive interaction between electrons, a phase transition to the
density-wave state is found at finite temperature. In the opposite case of
attractive interaction, no phase transition is found. With decreasing
temperature , the effective vertex of interaction between electrons
renormalizes toward a one-dimensional limit in a self-similar way with the
characteristic length (transverse to the magnetic field) decreasing as
( is a cutoff). Correlation functions have
new forms, previously unknown for conventional one-dimensional or
three-dimensional Fermi-liquids.Comment: 13 pages + 4 figures (included
Structure of the Fulde-Ferrell-Larkin-Ovchinnikov state in two-dimensional superconductors
Nonuniform superconducting state due to strong spin magnetism is studied in
two-dimensional type-II superconductors near the second order phase transition
line between the normal and the superconducting states. The optimum spatial
structure of the orderparameter is examined in systems with cylindrical
symmetric Fermi surfaces. It is found that states with two-dimensional
structures have lower free energies than the traditional one-dimensional
solutions, at low temperatures and high magnetic fields. For s-wave pairing,
triangular, square, hexagonal states are favored depending on the temperature,
while square states are favored at low temperatures for d-wave pairing. In
these states, orderparameters have two-dimensional structures such as square
and triangular lattices.Comment: 11 pages (LaTeX, revtex.sty), 3 figures; added reference
Diversity of Raft-Like Domains in Late Endosomes
BACKGROUND: Late endosomes, the last sorting station in the endocytic pathway before lysosomes, are pleiomorphic organelles composed of tubular elements as well as vesicular regions with a characteristic multivesicular appearance, which play a crucial role in intracellular trafficking. Here, we have investigated whether, in addition to these morphologically distinguishable regions, late endosomal membranes are additionally sub-compartmentalized into membrane microdomains. METHODOLOGY/PRINCIPAL FINDINGS: Using sub-organellar fractionation techniques, both with and without detergents, combined with electron microscopy, we found that both the limiting membrane of the organel and the intraluminal vesicles contain raft-type membrane domains. Interestingly, these differentially localized domains vary in protein composition and physico-chemical properties. CONCLUSIONS/SIGNIFICANCE: In addition to the multivesicular organization, we find that late endosomes contain cholesterol rich microdomains both on their limiting membrane and their intraluminal vesicles that differ in composition and properties. Implications of these findings for late endosomal functions are discussed
Magnetic-Field Variations of the Pair-Breaking Effects of Superconductivity in (TMTSF)2ClO4
We have studied the onset temperature of the superconductivity Tc_onset of
the organic superconductor (TMTSF)2ClO4, by precisely controlling the direction
of the magnetic field H. We compare the results of two samples with nearly the
same onset temperature but with different scattering relaxation time tau. We
revealed a complicated interplay of a variety of pair-breaking effects and
mechanisms that overcome these pair-breaking effects. In low fields, the linear
temperature dependences of the onset curves in the H-T phase diagrams are
governed by the orbital pair-breaking effect. The dips in the in-plane
field-angle phi dependence of Tc_onset, which were only observed in the
long-tau sample, provides definitive evidence that the field-induced
dimensional crossover enhances the superconductivity if the field direction is
more than about 19-degrees away from the a axis. In the high-field regime for
H//a, the upturn of the onset curve for the long-tau sample indicates a new
superconducting state that overcomes the Pauli pair-breaking effect but is
easily suppressed by impurity scatterings. The Pauli effect is also overcome
for H//b' by a realization of another state for which the maximum of
Tc_onset(phi) occurs in a direction different from the crystalline axes. The
effect on Tc_onset of tilting the applied field out of the conductive plane
suggests that the Pauli effect plays a significant role in determining
Tc_onset. The most plausible explanation of these results is that (TMTSF)2ClO4
is a singlet superconductor and exhibits Fulde-Ferrell-Larkin-Ovchinnikov
(FFLO) states in high fields.Comment: 12 pages, 10 figures. To be published in J. Phys. Soc. Jpn. (vol.77,
2008
Larkin-Ovchinnikov-Fulde-Ferrell state in quasi-one-dimensional superconductors
The properties of a quasi-one-dimensional (quasi-1D) superconductor with {\it
an open Fermi surface} are expected to be unusual in a magnetic field. On the
one hand, the quasi-1D structure of the Fermi surface strongly favors the
formation of a non-uniform state (Larkin-Ovchinnikov-Fulde-Ferrell (LOFF)
state) in the presence of a magnetic field acting on the electron spins. On the
other hand, a magnetic field acting on an open Fermi surface induces a
dimensional crossover by confining the electronic wave-functions wave-functions
along the chains of highest conductivity, which results in a divergence of the
orbital critical field and in a stabilization at low temperature of a cascade
of superconducting phases separated by first order transistions. In this paper,
we study the phase diagram as a function of the anisotropy. We discuss in
details the experimental situation in the quasi-1D organic conductors of the
Bechgaard salts family and argue that they appear as good candidates for the
observation of the LOFF state, provided that their anisotropy is large enough.
Recent experiments on the organic quasi-1D superconductor (TMTSF)ClO
are in agreement with the results obtained in this paper and could be
interpreted as a signature of a high-field superconducting phase. We also point
out the possibility to observe a LOFF state in some quasi-2D organic
superconductors.Comment: 24 pages+17 figures (upon request), RevTex, ORSAY-LPS-24109
Ginzburg-Landau-Gor'kov Theory of Magnetic oscillations in a type-II 2-dimensional Superconductor
We investigate de Haas-van Alphen (dHvA) oscillations in the mixed state of a
type-II two-dimensional superconductor within a self-consistent Gor'kov
perturbation scheme. Assuming that the order parameter forms a vortex lattice
we can calculate the expansion coefficients exactly to any order. We have
tested the results of the perturbation theory to fourth and eight order against
an exact numerical solution of the corresponding Bogoliubov-de Gennes
equations. The perturbation theory is found to describe the onset of
superconductivity well close to the transition point . Contrary to
earlier calculations by other authors we do not find that the perturbative
scheme predicts any maximum of the dHvA-oscillations below . Instead we
obtain a substantial damping of the magnetic oscillations in the mixed state as
compared to the normal state. We have examined the effect of an oscillatory
chemical potential due to particle conservation and the effect of a finite
Zeeman splitting. Furthermore we have investigated the recently debated issue
of a possibility of a sign change of the fundamental harmonic of the magnetic
oscillations. Our theory is compared with experiment and we have found good
agreement.Comment: 39 pages, 8 figures. This is a replacement of supr-con/9608004.
Several sections changed or added, including a section on the effect of spin
and the effect of a conserved number of particles. To be published in Phys.
Rev.
Crystalline Color Superconductivity
In any context in which color superconductivity arises in nature, it is
likely to involve pairing between species of quarks with differing chemical
potentials. For suitable values of the differences between chemical potentials,
Cooper pairs with nonzero total momentum are favored, as was first realized by
Larkin, Ovchinnikov, Fulde and Ferrell (LOFF). Condensates of this sort
spontaneously break translational and rotational invariance, leading to gaps
which vary periodically in a crystalline pattern. Unlike the original LOFF
state, these crystalline quark matter condensates include both spin zero and
spin one Cooper pairs. We explore the range of parameters for which crystalline
color superconductivity arises in the QCD phase diagram. If in some shell
within the quark matter core of a neutron star (or within a strange quark star)
the quark number densities are such that crystalline color superconductivity
arises, rotational vortices may be pinned in this shell, making it a locus for
glitch phenomena.Comment: 40 pages, LaTeX with eps figs. v2: New paragraph on Ginzburg-Landau
treatment of LOFF phase in section 5. References added. v3: Small changes
only. Version to appear in Phys. Rev.
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