302 research outputs found
Comment on ''Field-Enhanced Diamagnetism in the Pseudogap State of the Cuprate Bi2Sr2CaCu2O8+\delta Superconductor in an Intense Magnetic Field''
In the above mentioned letter by Wang et al. [Phys. Rev. Lett, 95, 247002
(2005)], magnetization measurements on two Bi_2Sr_2caCu_2O_8+delta samples are
reported. They claim that these experimental results support the vortex
scenario for the loss of phase coherence at Tc. On the contrary, we show in
this comment that they can be explained by means of the Ginzburg Landau theory
(under a total-enery cutoff) for the superconducting fluctuations above Tc.Comment: Final versio
Breakdown by a magnetic field of the superconducting fluctuations in the normal state: A simple phenomenological explanation
We first summarize our recent observations, through magnetization
measurements in different low-Tc superconductors, of a rather sharp
disappearance of the superconducting fluctuations in the normal state when the
magnetic field approaches Hc2(0), the upper critical field extrapolated to
T=0K. We propose that a crude phenomenological description of the observed
effects may be obtained if the quantum limits associated with the uncertainty
principle are introduced in the Gaussian-Ginzburg-Landau description of the
fluctuation-induced magnetization.Comment: LaTeX, 8 pages, including 2 eps figures. Proceedings of SNS'04,
Sitges, Spai
On the dilemma between percolation processes and fluctuating pairs as the origin of the enhanced conductivity above the superconducting transition in cuprates
The confrontation between percolation processes and superconducting
fluctuations to account for the observed enhanced in-plane electrical
conductivity above but near in cuprates is revisited. The cuprates
studied here, LaSrCuO,
BiSrCaCuO, and TlBaCaCuO, have
a different number of superconducting CuO layers per unit-cell length and
different Josephson coupling between them, and are optimally-doped to minimize
-inhomogeneities. The excellent chemical and structural quality of these
samples also contribute to minimize the effect of extrinsic
-inhomogeneities, a crucial aspect when analyzing the possible presence of
intrinsic percolative processes. Our analyses also cover the so-called high
reduced-temperature region, up to the resistivity rounding onset
. By using the simplest form of the effective-medium
theory, we show that possible emergent percolation processes alone cannot
account for the measured enhanced conductivity. In contrast, these measurements
can be quantitatively explained using the Gaussian-Ginzburg-Landau (GGL)
approach for the effect of superconducting fluctuations in layered
superconductors, extended to by including a total energy
cutoff, which takes into account the limits imposed by the Heisenberg
uncertainty principle to the shrinkage of the superconducting wavefunction. Our
analysis confirms the adequacy of this cutoff, and that the effective
periodicity length is controlled by the relative Josephson coupling between
superconducting layers. These conclusions are reinforced by analyzing one of
the recent works that allegedly discards the superconducting fluctuations
scenario while supporting a percolative scenario for the enhanced conductivity
above in cuprates.Comment: 13 pages, 7 figure
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