1,053 research outputs found
Properties of the phonon-induced pairing interaction in YBaCuO within the local density approximation
The properties of the phonon-induced interaction between electrons are
studied using the local density approximation (LDA). Restricting the electron
momenta to the Fermi surface we find generally that this interaction has a
pronounced peak for large momentum transfers and that the interband
contributions between bonding and antibonding band are of the same magnitude as
the intraband ones. Results are given for various symmetry averages of this
interaction over the Fermi surface. In particular, we find that the
dimensionless coupling constant in the d-wave channel , relevant for
superconductivity, is only 0.022, i.e., even about ten times smaller than the
small value of the s-wave channel. Similarly, the LDA contribution to the
resistivity is about a factor 10 times smaller than the observed resistivity
suggesting that phonons are not the important low-energy excitations in
high-T oxides.Comment: 6 pages, 7 figure
Critical dynamics, duality, and the exact dynamic exponent in extreme type II superconductors
The critical dynamics of superconductors is studied using renormalization
group and duality arguments. We show that in extreme type II superconductors
the dynamic critical exponent is given exactly by . This result does not
rely on the widely used models of critical dynamics. Instead, it is shown that
follows from the duality between the extreme type II superconductor and
a model with a critically fluctuating gauge field. Our result is in agreement
with Monte Carlo simulations.Comment: 7 pages, no figures; version accepted for publication in PR
Selfconsistent gauge-invariant theory of in-plane infrared response of high-Tc cuprate superconductors involving spin fluctuations
We report on results of our theoretical study of the in-plane infrared
conductivity of the high-Tc cuprate superconductors using the model where
charged planar quasiparticles are coupled to spin fluctuations. The
computations include both the renormalization of the quasiparticles and the
corresponding modification of the current-current vertex function (vertex
correction), which ensures gauge invariance of the theory and local charge
conservation in the system. The incorporation of the vertex corrections leads
to an increase of the total intraband optical spectral weight (SW) at finite
frequencies, a SW transfer from far infrared to mid infrared, a significant
reduction of the SW of the superconducting condensate, and an amplification of
characteristic features in the superconducting state spectra of the inverse
scattering rate 1/tau. We also discuss the role of selfconsistency and propose
a new interpretation of a kink occurring in the experimental low temperature
spectra of 1/tau around 1000cm^{-1}.Comment: 9 pages with 6 figures, submitted to Physical Review
Electronic theory for superconductivity in SrRuO: triplet pairing due to spin-fluctuation exchange
Using a two-dimensional Hubbard Hamiltonian for the three electronic bands
crossing the Fermi level in SrRuO we calculate the band structure and
spin susceptibility in quantitative agreement with
nuclear magnetic resonance (NMR) and inelastic neutron scattering (INS)
experiments. The susceptibility has two peaks at {\bf Q}
due to the nesting Fermi surface properties and at {\bf q}
due to the tendency towards ferromagnetism. Applying spin-fluctuation exchange
theory as in layered cuprates we determine from ,
electronic dispersions, and Fermi surface topology that superconductivity in
SrRuO consists of triplet pairing. Combining the Fermi surface topology
and the results for we can exclude and wave
symmetry for the superconducting order parameter. Furthermore, within our
analysis and approximations we find that -wave symmetry is slightly favored
over p-wave symmetry due to the nesting properties of the Fermi surface.Comment: 5 pages, 5 figures, misprints correcte
Effect of Nonmagnetic Impurity in Nearly Antiferromagnetic Fermi Liquid: Magnetic Correlations and Transport Phenomena
In nearly antiferromagnetic (AF) metals such as high-Tc superconductors
(HTSC's), a single nonmagnetic impurity frequently causes nontrivial widespread
change of the electronic states. To elucidate this long-standing issue, we
study a Hubbard model with a strong onsite impurity potential based on an
improved fluctuation-exchange (FLEX) approximation, which we call the GV^I-FLEX
method. This model corresponds to the HTSC with dilute nonmagnetic impurity
concentration. We find that (i) both local and staggered susceptibilities are
strongly enhanced around the impurity. By this reason, (ii) the quasiparticle
lifetime as well as the local density of states (DOS) are strongly suppressed
in a wide area around the impurity (like a Swiss cheese hole), which causes the
``huge residual resistivity'' beyond the s-wave unitary scattering limit. We
stress that the excess quasiparticle damping rate caused by impurities has
strong momentum-dependence due to non-s-wave scatterings induced by many-body
effects, so the structure of the ``hot spot/cold spot'' in the host system
persists against impurity doping. This result could be examined by the ARPES
measurements. In addition, (iii) only a few percent of impurities can causes a
``Kondo-like'' upturn of resistivity () at low temperatures when
the system is very close to the AF quantum critical point (QCP). The results
(i)-(iii) obtained in the present study, which cannot be derived by the simple
FLEX approximation, naturally explains the main impurity effects in HTSC's. We
also discuss the impurity effect in heavy fermion systems and organic
superconductors.Comment: 22 pages, to be published in PR
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