Fluctuation diamagnetism around the superconducting transition in a cuprate crystal with a reduced Meissner fraction

The magnetization around the superconducting transition was measured in a Tl$_{0.5}$Pb$_{0.5}$Sr$_2$CaCu$_2$O$_7$ crystal affected by a considerable reduction ($\sim$55%) of its effective superconducting volume fraction but still with a relatively sharp low-field Meissner transition, a behaviour that may be attributed to the presence of structural inhomogeneities. By taking into account these inhomogeneities just through the Meissner fraction, the observed diamagnetism may still be explained, consistently above and below the superconducting transition, in terms of the conventional Ginzburg-Landau approach with fluctuations of Cooper pairs and vortices.Comment: 4 pages, 4 figure

Magnetization vector in the reversible region of a highly anisotropic cuprate superconductor: anisotropy factor and the role of 2D vortex fluctuations

By using a high quality Tl2Ba2Ca2Cu3O10 (Tl-2223) single crystal as an example, the magnetization vector was probed in the reversible region of highly anisotropic cuprate superconductors. For that, we have measured its components along and transverse to the applied magnetic field for different crystal orientations. The analysis shows that the angular dependence of the perpendicular component of the magnetization vector follows the one predicted by a London-like approach which includes a contribution associated with the thermal fluctuations of the 2D vortex positions. For the Tl-2223 crystal studied here, a lower bound for the anisotropy factor was estimated to be about 190.Comment: 6 pages, 3 figure

Diamagnetism around the Meissner transition in a homogeneous cuprate single crystal

The in-plane diamagnetism around the Meissner transition was measured in a Tl$_2$Ba$_2$Ca$_2$Cu$_3$O$_{10}$ single crystal of high chemical and structural quality, which minimizes the inhomogeneity and disorder rounding effects on the magnetization. When analyzed quantitatively and consistently above and below the transition in terms of the Ginzburg-Landau (GL) approach with fluctuations of Cooper pairs and vortices, these data provide a further confirmation that the observed Meissner transition is a conventional GL superconducting transition in a homogeneous layered superconductor.Comment: 5 pages, including 3 figure

The diamagnetism above the superconducting transition in underdoped La(1.9)Sr(0.1)CuO(4) revisited: Chemical disorder or phase incoherent superconductivity?

The interplay between superconducting fluctuations and inhomogeneities presents a renewed interest due to recent works supporting an anomalous [beyond the conventional Gaussian-Ginzburg-Landau (GGL) scenario] diamagnetism above Tc in underdoped cuprates. This conclusion, mainly based in the observation of new anomalies in the low-field isothermal magnetization curves, is in contradiction with our earlier results in the underdoped La(1.9)Sr(0.1)CuO(4) [Phys. Rev. Lett. 84, 3157 (2000)]. These seemingly intrinsic anomalies are being presented in various influential works as a 'thermodynamic evidence' for phase incoherent superconductivity in the pseudogap regime, this last being at present a central and debated issue of the cuprate superconductors' physics. Here we have extended our magnetization measurements in La(1.9)Sr(0.1)CuO(4) to two samples with different chemical disorder, in one of them close to the one associated with the random distribution of Sr ions. For this sample, the corresponding Tc-distribution may be approximated as symmetric around the average Tc, while in the most disordered sample is strongly asymmetric. The comparison between the magnetization measured in both samples provides a crucial check of the chemical disorder origin of the observed diamagnetism anomalies, which are similar to those claimed as due to phase fluctuations by other authors. This conclusion applies also to the sample affected only by the intrinsic-like chemical disorder, providing then a further check that the intrinsic diamagnetism above the superconducting transition of underdoped cuprates is not affected by the opening of a pseudogap in the normal state. It is also shown here that once these disorder effects are overcome, the remaining precursor diamagnetism may be accounted at a quantitative level in terms of the GGL approach under a total energy cutoff.Comment: 13 pages, 7 figures. Minor corrections include

Comment on "High Field Studies of Superconducting Fluctuations in High-Tc Cuprates. Evidence for a Small Gap distinct from the Large Pseudogap"

By using high magnetic field data to estimate the background conductivity, Rullier-Albenque and coworkers have recently published [Phys.Rev.B 84, 014522 (2011)] experimental evidence that the in-plane paraconductivity in cuprates is almost independent of doping. In this Comment we also show that, in contrast with their claims, these useful data may be explained at a quantitative level in terms of the Gaussian-Ginzburg-Landau approach for layered superconductors, extended by Carballeira and coworkers to high reduced-temperatures by introducing a total-energy cutoff [Phys.Rev.B 63, 144515 (2001)]. When combined, these two conclusions further suggest that the paraconductivity in cuprates is conventional, i.e., associated with fluctuating superconducting pairs above the mean-field critical temperature.Comment: 9 pages, 1 figur

Anomalous precursor diamagnetism at low reduced magnetic fields and the role of Tc inhomogeneities in the superconductors Pb55In45 and underdoped La1.9Sr0.1CuO4

The magnetic field dependence of the magnetization was measured above the superconducting transition in a high-Tc underdoped cuprate La1.9Sr0.1CuO4 and in a low-Tc alloy (Pb55In45). Near the superconducting transition [typically for (T-Tc)/Tc<0.05] and under low applied magnetic field amplitudes [typically for H/Hc2(0)<0.01, where Hc2(0) is the corresponding upper critical field extrapolated to T=0 K] the magnetization of both samples presents a diamagnetic contribution much larger than the one predicted by the Gaussian Ginzburg-Landau (GGL) approach for superconducting fluctuations. These anomalies have been already observed in cuprate compounds by various groups and attributed to intrinsic effects associated with the own nature of these high-Tc superconductors. However, we will see here that our results in both high and low-Tc superconductors may be explained quantitatively, and consistently with the GGL behavior observed at higher fields, by just taking into account the presence in the samples of an uniform distribution of Tc inhomogeneities. These Tc inhomogeneities, which may be in turn associated with stoichiometric inhomogeneities, were estimated from independent measurements of the temperature dependence of the field-cooled magnetic susceptibility under low applied magnetic fields.Comment: 25 pages, including 6 figures and 1 table. Typos corrected. Compacte

High-temperature superconducting fault current microlimiters

High-temperature superconducting microbridges implemented with YBa(2)Cu(3)O(7-delta) thin-films are shown to be possible fault current limiters for microelectronic devices with some elements working at temperatures below the superconducting critical temperature and, simultaneously, under very low power conditions (below 1W). This is the case in the important applications of superconductors as SQUID based electronics, and technologies for communication or infrared detectors. In this paper it is shown that the good thermal behavior of these microlimiters allows working in a regime where even relatively small faults induce their transition to highly dissipative states, dramatically increasing their limitation efficiency. The conditions for optimal refrigeration and operation of these microlimiters are also proposed.Comment: 10 pages, 3 figures. LaTeX and EPS file