Preeminent role of the Van Hove singularity in the strong-coupling analysis of scanning tunneling spectroscopy for two-dimensional cuprates

In two dimensions the non-interacting density of states displays a Van Hove singularity (VHS) which introduces an intrinsic electron-hole asymmetry, absent in three dimensions. We show that due to this VHS the strong-coupling analysis of tunneling spectra in high-$T_c$ superconductors must be reconsidered. Based on a microscopic model which reproduces the experimental data with great accuracy, we elucidate the peculiar role played by the VHS in shaping the tunneling spectra, and show that more conventional analyses of strong-coupling effects can lead to severe errors.Comment: 5 pages, 4 figure

Doping effects in bi-based superconductors : Vortex phase diagrams and scanning tunneling spectroscopy

La supraconductivité est un phénomène qui fut découvert en 1911. Il se caractérise par l'absence de toute résistance électrique en dessous d'un certaine température dite température critique. Cette super-conductivité est accompagnée de l'expulsion totale de tout champ magnétique hors du matériau. La supraconductivité à basse température critique (entre 0 et 20K) est bien décrite par la théorie BCS, développée en 1957, mais les supraconducteurs à haute température critique (jusqu'à 157K) sont encore mal compris..

Céramiques haute température: apports de la modélisation thermodynamique

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Levy de Castro et al. Reply

A Reply to the Comment by Flora Onufrieva and Pierre Pfeuty

Vortex phase diagram and temperature-dependent second-peak effect in overdoped Bi₂Sr₂CuO_6+δ crystals

We study the vortex phase diagram of the single-layer Bi2Sr2CuO6+δ (Bi2201) superconductor by means of bulk magnetization measurements on high-quality oxygen-overdoped crystals. In striking contrast with the results found in the moderately doped two- and three-layer Bi-based cuprates, Bi2201 exhibits a strong temperature-dependent second-peak effect. By means of measurements of the in-plane and out-of-plane first-penetration field we provide direct evidence that this phenomenon is mainly associated to an increase in the electromagnetic anisotropy on warming. The effect of oxygen-doping δ on the vortex phase diagram results in both the irreversibility and second-peak lines shifting to higher temperatures and fields. This enhanced stability of the Bragg glass phase suggests that the interlayer coupling between Cu-O layers increases with δ. In addition, we found that the critical temperature follows the parabolic relation with the number of holes per Cu-O plane that holds for most single- and two-layer cuprates

Scanning tunneling spectroscopy of high T_c cuprates

Tunneling spectroscopy played a central role in the experimental verification of the microscopic theory of superconductivity in the classical superconductors. In the case of high-temperature superconductors (HTS), the initial attempts to adopt the same approach were hampered by various problems related to the complexity of these materials. The progresses made in synthesizing high quality samples, and the use of scanning tunneling microscopy/spectroscopy (STM/STS) on these compounds allowed to overcome the main difficulties. In this review we present some of the experimental highlights obtained with STM/STS techniques over the last decade. Most of the results confirm the fact that this new class of materials differ noticeably from the conventional BCS superconductors, and provide convincing arguments towards the understanding of the microscopic mechanisms at the origin of high-temperature superconductivit

S100A8/A9 mRNA induction in an ex vivo model of endotoxin tolerance: roles of IL-10 and IFNγ.

Septic syndromes are the leading cause of death in intensive care units. They are characterized by the development of immune dysfunctions such as endotoxin tolerance (ET), whose intensity and duration are associated with increased risk of nosocomial infections and mortality. Alarmins S100A8 and S100A9 have been shown to be increased after septic shock. Importantly, a delayed S100A9 mRNA increase predicts hospital-acquired infection in patients. The aim of this study was to investigate the regulation of S100A8 and S100A9 mRNA expression in an ex vivo model of ET.ET was reproduced ex vivo by priming healthy peripheral blood mononuclear cells (number of donors  = 9 to 10) with low-dose endotoxin (2 ng/ml) before stimulation with high dose endotoxin (100 ng/ml). S100A8 and S100A9 mRNA levels were measured by quantitative real-time polymerase chain reactions.ET was established by observing decreased TNFα and increased IL-10 transcriptomic responses to two subsequent endotoxin challenges. Interestingly, ET was associated with increased S100A8 and S100A9 mRNA expression ex vivo. We showed that IL-10 played a role in this process, since S100A8 and S100A9 mRNA increases were significantly abrogated by IL-10 blockade in the model. Conversely, treatment with rIFN-γ, a pro-inflammatory and immunostimulating molecule known to block ET induction, was able to restore normal S100A8 and S100A9 mRNA in this model.In this ex vivo model, we observed that S100A8 and S100A9 mRNA expression was significantly increased during ET. This reproduced ex vivo the observations we had previously made in septic shock patients. Interestingly, IL-10 blockade and rIFN-γ treatment partially abrogated S100A8/A9 mRNA increases in this model. Pending confirmation in larger, independent clinical studies, these preliminary results suggest that S100A8 and S100A9 mRNA levels might be used as surrogate markers of ET and as stratification tools for personalized immunotherapy in septic shock patients

S100A8 and S100A9 mRNA level increases were significantly abrogated by rIFN-γ in endotoxin tolerance model.

<p>Messenger RNA (mRNA) level of TNFα, IL-10, S100A8 and S100A9 in an <i>ex vivo</i> model of endotoxin tolerance. The mRNA level was normalized to that of the reference gene peptidylpropylisomerase B and then compared to the control group. Black columns represent controls (cells without any lipopolysaccharide (LPS)), white columns represent LPS-unprimed cells (only stimulated once with 100 ng/ml LPS) and grey columns represent LPS-primed cells (stimulated three times: 2 ng/ml LPS followed by vehicle or IFN-γ followed by 100 ng/ml LPS). †p<0.01, ‡p<0.05, Wilcoxon paired test. Median (+/− interquartile range) data from 10 independent experiments are given.</p

Quantitative PCR and primers.

a<p>Top sequence is forward primer, bottom is reverse.</p

Endotoxin tolerance is associated with decreased TNFα and increased IL-10, S100A8 and S100A9 mRNA expressions.

<p><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0100909#pone-0100909-g002" target="_blank">Figures 2A, B, C and D</a>. Messenger RNA (mRNA) level of tolerizable gene (TNFα) and non-tolerizable genes (IL-10, S100A8 and S100A9) in an <i>ex vivo</i> model of endotoxin tolerance. The mRNA level was normalized to that of the reference gene peptidylpropylisomerase B (PPIB) and then compared to the control group. Black columns represent controls (cells without any lipopolysaccharide (LPS)), white columns represent LPS-unprimed cells (only stimulated once with 100 ng/ml LPS), light grey columns represent LPS-primed cells (stimulated twice: 2 ng/ml followed by 100 ng/ml) and dark grey columns represent cells stimulated once with 2 ng/ml LPS without any second stimulation. **<0.01, *<0.05, Wilcoxon signed-rank test. Median (+/− interquartile range) data from 10 independent experiments are given. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0100909#pone-0100909-g002" target="_blank">Figure 2E</a>. Correlation between S100A8 mRNA expression (x-axis) and S100A9 mRNA expression (y-axis) in the endotoxin tolerance model. S100A8 and S100A9 mRNA levels were normalized to that of PPIB. Data were obtained from the 10 independent experiments described above.</p