Signatures of nematic quantum critical fluctuations in the Raman spectra of lightly doped cuprates

We consider the lightly doped cuprates Y$_{0.97}$Ca$_{0.03}$BaCuO$_{6.05}$ and La$_{2-x}$Sr$_x$CuO$_4$ (with $x=0.02$,0.04), where the presence of a fluctuating nematic state has often been proposed as a precursor of the stripe (or, more generically, charge-density wave) phase, which sets in at higher doping. We phenomenologically assume a quantum critical character for the longitudinal and transverse nematic, and for the charge-ordering fluctuations, and investigate the effects of these fluctuations in Raman spectra. We find that the longitudinal nematic fluctuations peaked at zero transferred momentum account well for the anomalous Raman absorption observed in these systems in the $B_{2g}$ channel, while the absence of such effect in the $B_{1g}$ channel may be due to the overall suppression of Raman response at low frequencies, associated with the pseudogap. While in Y$_{0.97}$Ca$_{0.03}$BaCuO$_{6.05}$ the low-frequency lineshape is fully accounted by longitudinal nematic collective modes alone, in La$_{2-x}$Sr$_x$CuO$_4$ also charge-ordering modes with finite characteristic wavevector are needed to reproduce the shoulders observed in the Raman response. This different involvement of the nearly critical modes in the two materials suggests a different evolution of the nematic state at very low doping into the nearly charge-ordered state at higher doping.Comment: 12 pages with 10 figures, to appear in Phys. Rev. B 201

Extended paraconductivity regime in underdoped cuprates

We reconsider transport experiments in strongly anisotropic superconducting cuprates and we find that universal Aslamazov-Larkin (AL) paraconductivity in two dimensions is surprisingly robust even in the underdoped regime below the pseudogap crossover temperature T^*. We also establish that the underlying normal state resistivity in the pseudogap phase is (almost) linear in temperature, with all the deviations being quantitatively accounted by AL paraconductivity. The disappearence of paraconductivity is governed by the disappearence of gaussian pair fluctuations at an energy scale related to T^*.Comment: 5 pages and 2 figure

Organic Acids and Nature Identical Compounds Can Increase the Activity of Conventional Antibiotics Against Clostridium Perfringens and Enterococcus Cecorum In Vitro

SUMMARY In a global context of increased antibiotic resistance, feed additives with enhanced antimicrobial properties are a useful and increasingly needed strategy. Organic acids (OA) and botanical molecules such as nature identical compounds (NIC) have been shown to be effective against bacterial infections based on their antimicrobial activity. The aim of this study was to evaluate whether the combination of OA or NIC with conventional antibiotics in poultry could increase antibiotic efficacy against Clostridium perfringens and Enterococcus cecorum. These organisms are the major poultry pathogens responsible for necrotic enteritis and bacterial chondronecrosis with osteomyelitis, respectively, and they have developed resistance to several antibiotics worldwide. A set of antimicrobial tests showed that both species had variable antibiotic sensitivity. Alternatively, OA and NIC were always effective in a dose-dependent manner, even when the antibiotics failed. For several strains, selected combinations of OA or NIC with antibiotics increased the bacterial sensitivity to antibiotics. Therefore, OA and NIC have potential to enhance the efficacy of conventional antibiotics against C. perfringens andE. cecorum

Doping-dependent competition between superconductivity and polycrystalline charge density waves

From systematic analysis of the high pulsed magnetic field resistance data of La$_{2-x}$Sr$_x$CuO$_{4}$ thin films, we extract an experimental phase diagram for several doping values ranging from the very underdoped to the very overdoped regimes. Our analysis highlights a competition between charge density waves and superconductivity which is ubiquitous between $x=0.08$ and $x=0.19$ and produces the previously observed double step transition. When suppressed by a strong magnetic field, superconductivity is resilient for two specific doping ranges centered around respectively $x\approx 0.09$ and $x\approx 0.19$ and the characteristic temperature for the onset of the competing charge density wave phase is found to vanish above $x = 0.19$. At $x=1/8$ the two phases are found to coexist exactly at zero magnetic field.Comment: 13 figures. Changes from previous version are in red. A few clarifications and a discussion about the different materials were added together with additional reference