2,689 research outputs found
Coupling of intrinsic Josephson oscillations in layered superconductors by charge fluctuations
The coupling of Josephson oscillations in layered superconductors is studied
with help of a tunneling Hamiltonian formalism. The general form of the current
density across the barriers between the superconducting layers is derived. The
induced charge fluctuations on the superconducting layers lead to a coupling of
the Josephson oscillations in different junctions. A simplified set of
equations is then used to study the non-linear dynamics of the system. In
particular the influence of the coupling on the current-voltage characteristics
is investigated and upper limits for the coupling strength are estimated from a
comparison with experiments on cuprate superconductors.Comment: To be published in proceedings of SPIE conference San Diego 199
Irrelevant Interactions without Composite Operators - A Remark on the Universality of Second Order Phase Transitions
We study the critical behaviour of symmetric theory including
irrelevant terms of the form in the bare action,
where is the UV cutoff (corresponding e.g. to the inverse lattice
spacing for a spin system). The main technical tool is renormalization theory
based on the flow equations of the renormalization group which permits to
establish the required convergence statements in generality and rigour. As a
consequence the effect of irrelevant terms on the critical behaviour may be
studied to any order without using renormalization theory for composite
operators. This is a technical simplification and seems preferable from the
physical point of view. In this short note we restrict for simplicity to the
symmetry class of the Ising model, i.e. one component theory. The
method is general, however.Comment: 13 page
Microscopic theory of the coupling of intrinsic Josephson oscillations and phonons
A microscopic theory for the coupling of intrinsic Josephson oscillations and
dispersive phonon branches in layered superconductors is developed. Thereby the
effect of phonons on the electronic c-axis transport enters through an
effective longitudinal dielectric function. This coupling provides an
explanation of recently observed subgap resonances in the --
curve of anisotropic cuprate superconductors forming a stack of short Josephson
junctions. Due to the finite dispersion these resonances can appear at
van-Hove-singularities of both optical and acoustical phonon branches,
explaining low-voltage structures in the I-V-characteristic, which are not
understood in phonon models without dispersion. In long junctions the
dispersion of collective electron-phonon modes parallel to the layers is
investigated.Comment: 4 pages, 3 figures, 1 table, espcrc2.sty, invited contribution to
"Materials and Mechanisms of Superconductivity and High Temperature
Superconductors VI - M2S-HTSC-VI", Houston, Texas, 20-25 Feb 2000, to appear
in Physica
Theory for the coupling between longitudinal phonons and intrinsic Josephson oscillations in layered superconductors
In this publication a microscopic theory for the coupling of intrinsic
Josephson oscillations in layered superconductors with longitudinal
c-axis-phonons is developed. It is shown that the influence of lattice
vibrations on the c-axis transport can be fully described by introducing an
effective longitudinal dielectric function. Resonances in the
I-V-characteristic appear at van Hove singularities of both acoustical and
optical longitudinal phonon branches. This provides a natural explanation of
the recently discovered subgap structures in the I-V-characteristic of highly
anisotropic cuprate superconductors. The effect of the phonon dispersion on the
damping of these resonances and the coupling of Josephson oscillations in
different resistive junctions due to phonons are discussed in detail.Comment: submitted to Phys. Rev. B, corrections following referee repor
Static Charge Coupling of Intrinsic Josephson Junction
A microscopic theory for the coupling of intrinsic Josephson oscillations due
to charge fluctuations on the quasi two-dimensional superconducting layers is
presented. Thereby in close analogy to the normal state the effect of the
scalar potential on the transport current is taken into account consistently.
The dispersion of collective modes is derived and an estimate of the coupling
constant is given. It is shown that the correct treatment of the quasiparticle
current is essential in order to get the correct position of Shapiro steps. In
this case the influence of the coupling on dc-properties like the -curve
is negligible.Comment: 6 pages latex, 5 figures, espcrc2.sty, Invited Contribution to "2nd
International Symposiom on Intrinsic Josephson Effects and Plasma
Oscillations in High-TC Superconductors", 22-24 August, Sendai, Japan, to be
published in Physica
Subgap structures in the current-voltage characteristic of the intrinsic Josephson effect due to phonons
A modified RSJ-model for the coupling of intrinsic Josephson oscillations and
c-axis phonons in the high-T_c superconductors Tl_2Ba_2Ca_2Cu_3O_{10+\delta}
and Bi_2Sr_2CaCu_2O_{8+\delta} is deveoped. This provides a very good
explanation for recently reported subgap structures in the I-V-characteristic
of the c-axis transport. It turns out that the voltages of these structures
coincide with the eigenfrequencies of longitudinal optical phonons, providing a
new measurement technique for this quantity. The significantly enhanced
microwave emission at the subgap structures in both the GHz and THz region is
discussed.Comment: correction of minor misprints, revtex, 3 pages, two postscript
figures, aps, epsf, Contributed Paper to the "International Symposion on the
Intrinsic Josphson effect and THz Plasma Oscillations", 22-25 February 1997,
Sendai, Japan; to be published in Physica
Coupling between phonons and intrinsic Josephson oscillations in cuprate superconductors
The recently reported subgap structures observed in the current-voltage
characteristic of intrinsic Josephson junctions in the high-T_c superconductors
Tl_2Ba_2Ca_2Cu_3O_{10+\delta} and Bi_2Sr_2CaCu_2O_{8+\delta} are explained by
the coupling between c-axis phonons and Josephson oscillations. A model is
developed where c-axis lattice vibrations between adjacent superconducting
multilayers are excited by the Josephson oscillations in a resistive junction.
The voltages of the lowest structures correspond well to the frequencies of
longitudinal c-axis phonons with large oscillator strength in the two
materials, providing a new measurement technique for this quantity.Comment: 4 pages, 3 figures, revtex, aps, epsf, psfig. submitted to Physical
Review Letters, second version improved in detai
Electronic compressibility and charge imbalance relaxation in cuprate superconductors
In the material SmLaSrCuO with alternating intrinsic
Josephson junctions we explain theoretically the relative amplitude of the two
plasma peaks in transmission by taking into account the spatial dispersion of
the Josephson Plasma Resonance in direction due to charge coupling. From
this and the magnetic field dependence of the plasma peaks in the vortex solid
and liquid states it is shown that the electronic compressibility of the
CuO layers is consistent with a free electron value. Also the London
penetration depth near can be
determined. The voltage response in the -curve of a
BiSrCaCuO mesa due to microwave irradiation or current
injection in a second mesa is related to the nonequilibrium charge imbalance of
quasiparticles and Cooper pairs and from our experimental data the relaxation
time is obtained.Comment: 2 pages, 2 figures, phc-proc4-auth.cls, to be published in Physica C
as a proceeding of M2S-HTSC Rio 200
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