904 research outputs found
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
Renormalization of the elementary excitations in hole- and electron-doped cuprates due to spin fluctuations
Extending our previous studies we present results for the doping-, momentum-,
frequency-, and temperature- dependence of the kink-like change of the
quasiparticle velocity resulting from the coupling to spin fluctuations. In the
nodal direction a kink is found in both the normal and superconducting state
while in the antinodal direction a kink occurs only below due to the
opening of the superconducting gap. A pronounced kink is obtained only for
hole-doped, but not for electron-doped cuprates and is characteristically
different from what is expected due to electron-phonon interaction. We further
demonstrate that the kink structure is intimately connected to the resonance
peak seen in inelastic neutron scattering. Our results suggest similar effects
in other unconventional superconductors like .Comment: revised version, 12 pages, 19 figures. accepted for publication in
PR
The Anomalous Infrared Emission of Abell 58
We present a new model to explain the excess in mid and near infrared
emission of the central, hydrogen poor dust knot in the planetary nebula (PN)
Abell 58. Current models disagree with ISO measurement because they apply an
average grain size and equilibrium conditions only. We investigate grain size
distributions and temperature fluctuations affecting infrared emission using a
new radiative transfer code and discuss in detail the conditions requiring an
extension of the classical description. The peculiar infrared emission of V605
Aql, the central dust knot in Abell 58, has been modeled with our code. V605
Aql is of special interest as it is one of only three stars ever observed to
move from the evolutionary track of a central PN star back to the post-AGB
state.Comment: 17 pages, 4 figures; accepted and to be published in Ap
Electronic States in the Antiferromagnetic Phase of Electron-Doped High-Tc Cuprates
We investigate the electronic states in the antiferromagnetic (AF) phase of
electron-doped cuprates by using numerically exact diagonalization technique
for a t-t'-t''-J model. When AF correlation develops with decreasing
temperature, a gaplike behavior emerges in the optical conductivity.
Simultaneously, the coherent motion of carriers due to the same sublattice
hoppings is enhanced. We propose that the phase is characterized as an AF state
with small Fermi surface around the momentum k=(\pi,0) and (0,\pi). This is a
remarkable contrast to the behavior of hole-doped cuprates.Comment: RevTeX, 5 pages, 4 figures, to appear in Phys. Rev. B Brief Report
Interplay between electron-phonon and Coulomb interactions in cuprates
Evidence for strong electron-phonon coupling in high-Tc cuprates is reviewed,
with emphasis on the electron and phonon spectral functions. Effects due to the
interplay between the Coulomb and electron-phonon interactions are studied. For
weakly doped cuprates, the phonon self-energy is strongly reduced due to
correlation effects, while there is no corresponding strong reduction for the
electron self-energy. Polaron formation is studied, focusing on effects of
Coulomb interaction and antiferromagnetic correlations. It is argued that
experimental indications of polaron formation in undoped cuprates are due to a
strong electron-phonon interaction for these systems.Comment: 43 pages and 22 figure
Doping dependence of the many-body effects along the nodal direction in the high-Tc cuprate (Bi,Pb)_2Sr_2CaCu_2O_8
Angle-resolved photoemission spectroscopy (ARPES) is used to study the doping
dependence of the lifetime and the mass renormalization of the low energy
excitations in the high-Tc cuprate (Bi,Pb)_2Sr_2CaCu_2O_8 along the zone
diagonal. We find a linear energy de-pendence of the scattering rate for the
underdoped samples and a quadratic energy depend-ence in the overdoped case.
The mass enhancement of the quasiparticles due to the many body effects at the
Fermi energy is found to be in the order of 2 and the renormalization extends
over a large energy range for both the normal and the superconducting state.
The much discussed kink in the dispersion around 70 meV is interpreted as a
small additional effect at low temperatures.Comment: 12 pages, 3 figure
Interplay of ferromagnetism and triplet superconductivity in a Josephson junction
In this paper we extend our earlier analysis of the novel Josephson effect in
triplet superconductor--ferromagnet--triplet superconductor (TFT) junctions [B.
Kastening \emph{et al.}, Phys. Rev. Lett. {\bf{96}}, 047009 (2006)]. In our
more general formulation of the TFT junction we allow for potential scattering
at the barrier and an arbitrary orientation of the ferromagnetic moment.
Several new effects are found upon the inclusion of these extra terms: for
example, we find that a Josephson current can flow even when there is vanishing
phase difference between the superconducting condensates on either side of the
barrier. The critical current for a barrier with magnetization parallel to the
interface is calculated as a function of the junction parameters, and is found
to display strong non-analyticities. Furthermore, the Josephson current
switches first identified in our previous work are found to be robust features
of the junction, while the unconventional temperature-dependence of the current
is very sensitive to the extra terms in the barrier Hamiltonian.Comment: 24 pages, 15 figure
Theory for phonon-induced superconductivity in MgB
We analyze superonductivity in MgB observed below K resulting
from electron-phonon coupling involving a mode at meV and
most importantly the in-plane B-B vibration at
meV. The quasiparticles originating from - and -states couple
strongly to the low-frequency mode and the -vibrations respectively.
Using two-band Eliashberg theory, and , we calculate the gap functions (,
).
Our results provide an explanation of recent tunneling experiments.
We get .Comment: revised version, accepted for publication in PR
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