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

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

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

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

An Enduring Philosophical Agenda. Worldview Construction as a Philosophical Method\ud

Is there such a thing as a philosophical method? It seems that there are as many philosophical methods as there are philosophies. A method is any procedure employed to achieve a certain aim. So, before proposing a method, we have to tackle the delicate question: “what is the aim of philosophy?”. At the origin of philosophy, there is a questioning about the world. The worldview approach developed by Leo Apostel elegantly explicit those fundamental questions. As we answer them, we come up with a worldview. Using this framework, this paper consider answering this enduring philosophical agenda as the primary aim of philosophy. We illustrate the approach by pointing out the limitations of both a strictly scientific worldview and a strictly religious worldview. We then argue that philosophical worldviews constitute a particular class of possible worldviews. With the help of three analogies, we give guidelines to construct such worldviews. The next step is to compare the relative strength of philosophical worldviews. Precise evaluation standards to compare and confront worldviews are proposed. Some problems for worldview diffusion are then expounded. We close with basic hypotheses to build a comprehensive philosophical worldview

An Enduring Philosophical Agenda. Worldview Construction as a Philosophical Method

Is there something like a philosophical method? It seems that there are as many methods as there are philosophies. A method is any procedure employed to attain a certain end. So, before going to a method, we have to ask: what is the aim of philosophy? At the origin of philosophy, there is a questioning about the world. Leo Apostel and Jan Van der Veken made more precise and explicit those fundamental questions (Apostel, Van der Veken 1991). The primarily aim of philosophy can be seen as answering this philosophical agenda; with the answers, one come up with a worldview. We'll argue that the philosophical worldviews constitute a particular class of the possible worldviews. With the help of three analogies, we'll give some guidelines to construct such worldviews. But, what are the best philosophical worldviews? We'll see how we can compare and confront them; and also some problems for their diffusion. The last section will propose some basic hypotheses to build such integrative worldviews

Entanglement Renormalization: an introduction

We present an elementary introduction to entanglement renormalization, a real space renormalization group for quantum lattice systems. This manuscript corresponds to a chapter of the book "Understanding Quantum Phase Transitions", edited by Lincoln D. Carr (Taylor & Francis, Boca Raton, 2010)Comment: v2: new format. 24 pages, 10 figures, 2 tables, chapter of the book "Understanding Quantum Phase Transitions", edited by Lincoln D. Carr (Taylor & Francis, Boca Raton, 2010