225 research outputs found
Intrinsic Josephson Effect and Violation of the Josephson Relation in Layered Superconductors
Equations describing the resistive state of a layered superconductor with
anisotropic pairing are derived. The similarity with a stack of Josephson
junctions is found at small voltages only, when current density in the
direction perpendicular to the layers can be interpreted as a sum of the
Josephson superconducting, the Ohmic dissipative and the interference currents.
In the spatially uniform state differential conductivity at higher voltages
becomes negative. Nonuniformity of the current distribution generates the
branch imbalance and violates the Josephson relation between frequency and
voltage.Comment: 11 pages, no figures, revtex, to be published in Phys. Rev. Let
Linear response and collective oscillations in superconductors with d-wave pairing
Simple and physically transparent equations for the linear response of
layered superconductors with d-wave symmetry of the order parameter are derived
by means of the quasiclassic kinetic theory of superconductivity. Responses to
solenoidal and potential electric fields have different frequency dependencies.
The conductivity describing the response to the solenoidal field is limited by
the momentum relaxation, like in a normal metal. The response to the potential
electric field depends, in addition, on the branch imbalance relaxation rate.
The damping of plasma oscillations of superconducting electrons is determined
by dielectric relaxation and is small. Relaxation of branch imbalance
determined by elastic scattering is large enough to make the Carlson-Goldman
mode in d-wave superconductors overdamped.Comment: 11 pages, latex, no figures, submitted to Physical Review
On Effect of Equilibrium Fluctuations on Superfluid Density in Layered Superconductors
We calculate suppression of inter- and intralayer superconducting currents
due to equilibrium phase fluctuations and find that, in contrast to a recent
prediction, the effect of thermal fluctuations cannot account for linear
temperature dependence of the superfluid density in high-Tc superconductors at
low temperatures. Quantum fluctuations are found to dominate over thermal
fluctuations at low temperatures due to hardening of their spectrum caused by
the Josephson plasma resonance. Near Tc sizeable thermal fluctuations are found
to suppress the critical current in the stack direction stronger, than in the
direction along the layers. Fluctuations of quasiparticle branch imbalance make
the spectral density of voltage fluctuations at small frequencies non zero, in
contrast to what may be expected from a naive interpretation of Nyquist
formula.Comment: 5 pages, LaTeX, RevTeX, Submitted to PR
Convective Term and Transversely Driven Charge-Density Waves
We derive the convective terms in the damping which determine the structure
of the moving charge-density wave (CDW), and study the effect of a current
flowing transverse to conducting chains on the CDW dynamics along the chains.
In contrast to a recent prediction we find that the effect is orders of
magnitude smaller, and that contributions from transverse currents of electron-
and hole-like quasiparticles to the force exerted on the CDW along the chains
act in the opposite directions. We discuss recent experimental verification of
the effect and demonstrate experimentally that geometry effects might mimic the
transverse current effect.Comment: RevTeX, 9 pages, 1 figure, accepted for publications in PR
Reflectivity and Microwave Absorption in Crystals with Alternating Intrinsic Josephson Junctions
We compute the frequency and magnetic field dependencies of the reflectivity
in layered superconductors with two alternating intrinsic Josephson
junctions with different critical current densities and quasiparticle
conductivities for the electric field polarized along the c-axis. The parameter
describing the electronic compressibility of the layers and the charge
coupling of neighboring junctions was extracted for the
SmLaSrCuO superconductor from two independent
optical measurements, the fit of the loss function at zero magnetic
field and the magnetic field dependence of the peak positions in .
The experiments are consistent with a free electron value for near
the Josephson plasma frequencies.Comment: 4 pages, 4 postscript figures, misprints in table correcte
Coupling of the lattice and superlattice deformations and hysteresis in thermal expansion for the quasi one-dimensional conductor TaS
An original interferometer-based setup for measurements of length of
needle-like samples is developed, and thermal expansion of o-TaS crystals
is studied. Below the Peierls transition the temperature hysteresis of length
is observed, the width of the hysteresis loop being up to . The behavior of the loop is anomalous: the length changes so
that it is in front of its equilibrium value. The hysteresis loop couples with
that of conductivity. The sign and the value of the length hysteresis are
consistent with the strain dependence of the charge-density waves (CDW) wave
vector. With lowering temperature down to 100 K the CDW elastic modulus grows
achieving a value comparable with the lattice Young modulus. Our results could
be helpful in consideration of different systems with intrinsic
superstructures.Comment: 4 pages, 3 figures. Phys. Rev. Lett., accepted for publicatio
Optical Properties of Crystals with Spatial Dispersion: Josephson Plasma Resonance in Layered Superconductors
We derive the transmission coefficient, , for grazing incidence of
crystals with spatial dispersion accounting for the excitation of multiple
modes with different wave vectors for a given frequency . The
generalization of the Fresnel formulas contains the refraction indices of these
modes as determined by the dielectric function . Near
frequencies , where the group velocity vanishes, depends
also on an additional parameter determined by the crystal microstructure. The
transmission is significantly suppressed, if one of the excited modes is
decaying into the crystal. We derive these features microscopically for the
Josephson plasma resonance in layered superconductors.Comment: 4 pages, 2 figures, epl.cls style file, minor change
Non-equilibrium current noise in mesoscopic disordered SNS junctions
Current noise in superconductor-normal metal-superconductor (SNS) junctions
is calculated within the scattering theory of multiple Andreev reflections
(MAR). It is shown that the noise exhibits subharmonic gap singularities at
, both in single-mode junctions with arbitrary
transparency and in multi-mode disordered junctions. The subharmonic
structure is superimposed with monotonic increase of the effective transferred
charge with decreasing bias voltage. Other features of the
noise include a step-like increase of in junctions with small , and a
divergence at small voltages and excess noise , where is the excess current, at large voltages, in
junctions with diffusive transport.Comment: 5 page
Adiabatic Dynamics of Superconducting Quantum Point Contacts
Starting from the quasiclassical equations for non-equilibrium Green's
functions we derive a simple kinetic equation that governs ac Josephson effect
in a superconducting quantum point contact at small bias voltages. In contrast
to existing approaches the kinetic equation is valid for voltages with
arbitrary time dependence. We use this equation to calculate
frequency-dependent linear conductance, and dc characteristics with
and without microwave radiation for resistively shunted quantum point contacts.
A novel feature of the characteristics is the excess current
appearing at small voltages. An important by-product of our
derivation is the analytical proof that the microscopic expression for the
current coincides at arbitrary voltages with the expression that follows from
the Bogolyubov-de Gennes equations, if one uses appropriate amplitudes of
Andreev reflection which contain information about microscopic structure of the
superconductors.Comment: 12 Pages, REVTEX 3.0, 3 figures available upon reques
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