230 research outputs found
Thermodynamic Potential for Superfluid 3He in Aerogel
We present a free energy functional for superfluid 3He in the presence of
homogeneously distributed impurity disorder which extends the Ginzburg-Landau
free energy functional to all temperatures. We use the new free energy
functional to calculate the thermodynamic potential, entropy, heat capacity and
density of states for the B-phase of superfluid 3He in homogeneous, isotropic
aerogel.Comment: 10 pages, 4 figure
Theory of the Normal/Superfluid interface in population imbalanced Fermi gases
We present a series of theoretical studies of the boundary between a
superfluid and normal region in a partially polarized gas of strongly
interacting fermions. We present mean-field estimates of the surface energy in
this boundary as a function of temperature and scattering length. We discuss
the structure of the domain wall, and use a previously introduced
phenomonological model to study its influence on experimental observables.
Our microscopic mean-field calculations are not consistent with the magnitude
of the surface tension found from our phenomonological modelling of data from
the Rice experiments. We conclude that one must search for novel mechanisms to
explain the experiments.Comment: 15 pages, 9 figures (13 subfigures) -- v2: minor change
Reentrant vortex lattice transformation in four-fold symmetric superconductors
The physics behind the rhombicsquarerhombic flux line lattice
transformation in increasing fields is clarified on the basis of Eilenberger
theory. We demonstrate that this reentrance observed in LuNiBC is due
to intrinsic competition between superconducting gap and Fermi surface
anisotropies. The calculations reproduce not only it but also predict yet not
found lock-in transition to a square lattice with different orientation in
higher field. In view of physical origin given, this sequence of transitions is
rather generic to occur in four-fold symmetric superconductors.Comment: 5 pages, 4 figures,submitted to Phys. Rev. Let
Anisotropy of the upper critical field in superconductors with anisotropic gaps. Anisotropy parameters of MgB2
The upper critical field Hc2 is evaluated for weakly-coupled two-band
superconductors. By modeling the actual bands and the gap distribution of MgB2
by two Fermi surface spheroids with average parameters of the real material, we
show that H_{c2,ab}/H_{c2,c} increases with decreasing temperature in agreement
with available data.Comment: 4 pages, 2 figure
Supercurrent in a mesoscopic proximity wire
Recent experiments on the proximity induced supercurrent in mesoscopic normal
wires revealed a surprising temperature dependence. They suggest clean-limit
behavior although the wires are strongly disordered. We demonstrate that this
unexpected scaling is actually contained in the conventional description of
diffusive superconductors and find excellent agreement with the experimental
results. In addition we propose a SQUID-like proximity structure for further
experimental investigations of the effects in question.Comment: 6 pages LaTeX, 4 postscript figures; to appear in J. Low Temp. Phys.
(Proceedings of WSS '96
Mixed-State Thermodynamics of Superconductors with Moderately Large Paramagnetic Effects
Effects of Pauli paramagnetism on thermodynamic quantities in a vortex state,
such as the specific heat and magnetization , are studied using the
quasiclassical Eilenberger formalism. We demonstrate that with an increase of
paramagnetic depairing effect, the sigh of the curvature of the field
dependence of changes from negative to positive, and that the Maki
parameter becomes an increasing function of temperature. Our results
provide a natural explanation for the unusual field dependence of seen in
CeCoIn in terms of the paramagnetic effect.Comment: Published in J. Phys. Soc. Jpn. 74, 2181 (2005
- and -wave components induced around a vortex in -wave superconductors
Vortex structure of -wave superconductors is microscopically
analyzed in the framework of the quasi-classical Eilenberger equations. If the
pairing interaction contains an -wave (-wave) component in addition
to a -wave component, the -wave (-wave) component of
the order parameter is necessarily induced around a vortex in
-wave superconductors. The spatial distribution of the induced
-wave and -wave components is calculated. The -wave component has
opposite winding number around vortex near the -vortex core and
its amplitude has the shape of a four-lobe clover. The amplitude of
-component has the shape of an octofoil. These are consistent with
results based on the GL theory.Comment: RevTex,9 pages, 6 figures in a uuencoded fil
Hall Effect in the mixed state of moderately clean superconductors
The Hall conductivity in the mixed state of a clean () type-II
s-wave superconductor is determined from a microscopic calculation within a
quasiclassical approximation. We find that below the superconducting transition
the contribution to the transverse conductivity due to dynamical fluctuations
of the order parameter is compensated by the modification of the quasiparticle
contribution. In this regime the nonlinear behaviour of the Hall angle is
governed by the change in the effective quasiparticle scattering rate due to
the reduction in the density of states at the Fermi level. The connection with
experimental results is discussed
Entropy and Spin Susceptibility of s-wave Type-II Superconductors near
A theoretical study is performed on the entropy and the spin
susceptibility near the upper critical field of s-wave
type-II superconductors with arbitrary impurity concentrations. The changes of
these quantities through may be expressed as , for example, where is the average flux density
and denotes entropy in the normal state. It is found that the
slopes and at T=0 are identical, connected
directly with the zero-energy density of states, and vary from 1.72 in the
dirty limit to in the clean limit. This mean-free-path dependence
of and at T=0 is quantitatively the same as that
of the slope for the flux-flow resistivity studied
previously. The result suggests that and near
T=0 are convex downward (upward) in the dirty (clean) limit, deviating
substantially from the linear behavior . The specific-heat
jump at also shows fairly large mean-free-path dependence.Comment: 8 pages, 5 figure
A Two-dimensional Superconductor in a Tilted Magnetic Field - new states with finite Cooper-pair momentum
Varying the angle Theta between applied field and the conducting planes of a
layered superconductor in a small interval close to the plane-parallel field
direction, a large number of superconducting states with unusual properties may
be produced. For these states, the pair breaking effect of the magnetic field
affects both the orbital and the spin degree of freedom. This leads to pair
wave functions with finite momentum, which are labeled by Landau quantum
numbers 0<n<\infty. The stable order parameter structure and magnetic field
distribution for these states is found by minimizing the quasiclassical free
energy near H_{c2} including nonlinear terms. One finds states with coexisting
line-like and point-like order parameter zeros and states with coexisting
vortices and antivortices. The magnetic response may be diamagnetic or
paramagnetic depending on the position within the unit cell. The structure of
the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states at Theta=0 is reconsidered.
The transition n->\infty of the paramagnetic vortex states to the FFLO-limit is
analyzed and the physical reason for the occupation of higher Landau levels is
pointed out.Comment: 24 pages, 11 figure
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