284 research outputs found
Long-range order in the A-like phase of superfluid 3He in aerogel
A mutual action of the random anisotropy brought in the superfluid 3He by
aerogel and of the global anisotropy caused by its deformation is considered.
Strong global anisotropy tends to suppress fluctuations of orientation of the
order parameter and stabilizes ABM order parameter. In a limit of vanishing
anisotropy these fluctuations are getting critical. It is argued that still in
a region of small fluctuations the average order parameter can acquire "robust"
component. This component maintains a long-range order even in a limit of
vanishing global anisotropy.Comment: A contribution to QFS 2007 in Kazan, revised for publication in the
Proceeding
Anomalous Charge Dynamics in the Superconducting State of Underdoped Cuprates
We present fermi liquid expressions for the low temperature behavior of the
superfluid stiffness, explain why they differ from those suggested recently by
Lee and Wen, and discuss their applicability to data on high-
superconductors. We find that a consistent description requires a strong,
doping dependent anisotropy, which affects states near the zone corners much
more strongly than those near the zone diagonals
Superfluid states with moving condensate in nuclear matter
Superfluid states of symmetric nuclear matter with finite total momentum of
Cooper pairs (nuclear LOFF phase) are studied with the use of Fermi-liquid
theory in the model with Skyrme effective forces. It is considered the case of
four-fold splitting of the excitation spectrum due to finite superfluid
momentum and coupling of T=0 and T=1 pairing channels. It has been shown that
at zero temperature the energy gap in triplet-singlet (TS) pairing channel (in
spin and isospin spaces) for the SkM force demonstrates double-valued
behavior as a function of superfluid momentum. As a consequence, the phase
transition at the critical superfluid momentum from the LOFF phase to the
normal state will be of a first order. Behavior of the energy gap as a function
of density for TS pairing channel under increase of superfluid momentum changes
from one-valued to universal two-valued. It is shown that two-gap solutions,
describing superposition of states with singlet-triplet (ST) and TS pairing of
nucleons appear as a result of branching from one-gap ST solution. Comparison
of the free energies shows that the state with TS pairing of nucleons is
thermodynamically most preferable.Comment: Report on DAAD summer school "Dense matter in Particle- and
Astrophysics". Prepared with RevTeX4, 5p., 4 eps figure
Tilt Modulus and Angle-Dependent Flux Lattice Melting in the Lowest Landau Level Approximation
For a clean high-T superconductor, we analyze the Lawrence-Doniach free
energy in a tilted magnetic field within the lowest Landau level (LLL)
approximation. The free energy maps onto that of a strictly -axis field, but
with a reduced interlayer coupling. We use this result to calculate the tilt
modulus of a vortex lattice and vortex liquid. The vortex contribution
to can be expressed in terms of the squared -axis Josephson plasmon
frequency . The transverse component of the field has very
little effect on the position of the melting curve.Comment: 8 pages, 2 figures, accepted for publication in Physical Review B
(Rapid Communications
Hall effect and geometric phases in Josephson junction arrays
Since effectively the local contact vortex velocity dependent part of the Magnus force in a Josephson junction array is zero in the classical limit, we predict zero classical Hall effect. In the quantum limit because of the geometric phases due to the finite superfluid density at superconductor grains, rich and complex Hall effect is found in this quantum regime due to the Thouless-Kohmoto-Nightingale-den-Nijs effect
Josephson current in superconductor-ferromagnet structures with a nonhomogeneous magnetization
We calculate the dc Josephson current for two types of
superconductor-ferromagnet (S/F) Josephson junctions. The junction of the first
type is a S/F/S junction. On the basis of the Eilenberger equation, the
Josephson current is calculated for an arbitrary impurity concentration. If the expression for the Josephson critical current is reduced
to that which can be obtained from the Usadel equation ( is the exchange
energy, is the momentum relaxation time). In the opposite limit
the superconducting condensate oscillates with period and
penetrates into the F region over distances of the order of the mean free path
. For this kind of junctions we also calculate in the case when the F
layer presents a nonhomogeneous (spiral) magnetic structure with the period
. It is shown that for not too low temperatures, the -state which
occurs in the case of a homogeneous magnetization (Q=0) may disappear even at
small values of . In this nonhomogeneous case, the superconducting
condensate has a nonzero triplet component and can penetrate into the F layer
over a long distance of the order of . The junction
of the second type consists of two S/F bilayers separated by a thin insulating
film. It is shown that the critical Josephson current depends on the
relative orientation of the effective exchange field of the bilayers. In
the case of an antiparallel orientation, increases with increasing .
We establish also that in the F film deposited on a superconductor, the
Meissner current created by the internal magnetic field may be both diamagnetic
or paramagnetic.Comment: 13 pages, 11 figures. To be published in Phys. Rev.
Analytical solution of the Gross-Neveu model at finite density
Recent numerical calculations have shown that the ground state of the
Gross-Neveu model at finite density is a crystal. Guided by these results, we
can now present the analytical solution to this problem in terms of elliptic
functions. The scalar potential is the superpotential of the non-relativistic
Lame Hamiltonian. This model can also serve as analytically solvable toy model
for a relativistic superconductor in the Larkin-Ovchinnikov-Fulde-Ferrell
phase.Comment: 5 pages, no figures, revtex; vs2: appendix with analytical proof of
self-consistency adde
Magnetoresistance and dephasing in a two-dimensional electron gas at intermediate conductances
We study, both theoretically and experimentally, the negative
magnetoresistance (MR) of a two-dimensional (2D) electron gas in a weak
transverse magnetic field . The analysis is carried out in a wide range of
zero- conductances (measured in units of ), including the range
of intermediate conductances, . Interpretation of the experimental
results obtained for a 2D electron gas in GaAs/InGaAs/GaAs single
quantum well structures is based on the theory which takes into account terms
of higher orders in , stemming from both the interference contribution and
the mutual effect of weak localization (WL) and Coulomb interaction. We
demonstrate that at intermediate conductances the negative MR is described by
the standard WL "digamma-functions" expression, but with a reduced prefactor
. We also show that at not very high the second-loop corrections
dominate over the contribution of the interaction in the Cooper channel, and
therefore appear to be the main source of the lowering of the prefactor,
. We further analyze the regime of a "weak insulator",
when the zero- conductance is low due to the localization at low
, whereas the Drude conductance is high, In this regime, while the
MR still can be fitted by the digamma-functions formula, the experimentally
obtained value of the dephasing rate has nothing to do with the true one. The
corresponding fitting parameter in the low- limit is determined by the
localization length and may therefore saturate at , even though the
true dephasing rate vanishes.Comment: 36 pages, 16 figure
Elastic Chain in a Random Potential: Simulation of the Displacement Function and Relaxation
We simulate the low temperature behaviour of an elastic chain in a random
potential where the displacements are confined to the {\it longitudinal}
direction ( parallel to ) as in a one dimensional charge density
wave--type problem. We calculate the displacement correlation function and the size dependent average square displacement
. We find that with
at short distances and at intermediate
distances. We cannot resolve the asymptotic long distance dependence of
upon . For the system sizes considered we find with . The exponent is in agreement
with the Random Manifold exponent obtained from replica calculations and the
exponent is consistent with an exact solution for the chain
with {\it transverse} displacements ( perpendicular to ).The
distribution of nearest distances between pinning wells and chain-particles is
found to develop forbidden regions.Comment: 19 pages of LaTex, 6 postscript figures available on request,
submitted to Journal of Physics A, MAJOR CHANGE
Detection of Striped Superconductors Using Magnetic Field Modulated Josephson Effect
In a very interesting recent Letter\cite{berg}, the authors suggested that a
novel form of superconducting state is realized in LaBaCuO with
close to 1/8. This suggestion was based on experiments\cite{li} on this
compound which found predominantly two-dimensional (2D) characters of the
superconducting state, with extremely weak interplane coupling. Later this
specific form of superconducting state was termed striped
superconductors\cite{berg08}. The purpose of this note is to point out that the
suggested form\cite{berg} of the superconducting order parameter can be
detected directly using magnetic field modulated Josephson effect.Comment: Expanded version as appeared in prin
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