1,208 research outputs found
Theory of fluctuation conductivity from interband pairing in pnictide superconductors
We derive the effective action for superconducting fluctuations in a
four-band model for pnictides, discussing the emergence of a single critical
mode out of a dominant interband pairing mechanism. We then apply our model to
calculate the paraconductivity in two-dimensional and layered three-dimensional
systems, and compare our results with recent resistivity measurements in
SmFeAsOFComment: 4 pages, 1 figure; final versio
Effect of mesoscopic inhomogeneities on local tunnelling density of states
We carry out a theoretical analysis of the momentum dependence of the
Fourier-transformed local density of states (LDOS) in the superconducting
cuprates within a model considering the interference of quasiparticles
scattering on quenched impurities. The impurities introduce an external
scattering potential, which is either nearly local in space or it can acquire a
substantial momentum dependence due to a possible strong momentum dependence of
the electronic screening near a charge modulation instability. The key new
effect that we introduce is an additional mesoscopic disorder aiming to
reproduce the inhomogeneities experimentally observed in scanning tunnelling
microscopy. The crucial effect of this mesoscopic disorder is to give rise to
point-like spectroscopic features, to be contrasted with the curve-like shape
of the spectra previously calculated within the interfering-quasiparticle
schemes. It is also found that stripe-like charge modulations play a relevant
role to correctly reproduce all the spectral features of the experiments.Comment: 11 pages and 5 figure
Signatures of nematic quantum critical fluctuations in the Raman spectra of lightly doped cuprates
We consider the lightly doped cuprates YCaBaCuO
and LaSrCuO (with ,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 channel, while the absence of such effect in the channel
may be due to the overall suppression of Raman response at low frequencies,
associated with the pseudogap. While in YCaBaCuO the
low-frequency lineshape is fully accounted by longitudinal nematic collective
modes alone, in LaSrCuO 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
Charge-fluctuation contribution to the Raman response in superconducting cuprates
We calculate the Raman response contribution due to collective modes, finding
a strong dependence on the photon polarizations and on the characteristic
wavevectors of the modes. We compare our results with recent Raman spectroscopy
experiments in underdoped cuprates, and
, where anomalous low-energy peaks are
observed, which soften upon lowering the temperature. We show that the specific
dependence on doping and on photon polarizations of these peaks is only
compatible with charge collective excitations at finite wavelength.Comment: 5 pages, 3 figure
Wo3 and ionic liquids: A synergic pair for pollutant gas sensing and desulfurization
This review deals with the notable results obtained by the synergy between ionic liquids (ILs) and WO3 in the field of pollutant gas sensing and sulfur removal pretreatment of fuels. Starting from the known characteristics of tungsten trioxide as catalytic material, many authors have proposed the use of ionic liquids in order to both direct WO3 production towards controllable nanostructures (nanorods, nanospheres, etc.) and to modify the metal oxide structure (incorporating ILs) in order to increase the gas adsorption ability and, thus, the catalytic efficiency. Moreover, ionic liquids are able to highly disperse WO3 in composites, thus enhancing the contact surface and the catalytic ability of WO3 in both hydrodesulfurization (HDS) and oxidative desulfurization (ODS) of liquid fuels. In particular, the use of ILs in composite synthesis can direct the hydrogenation process (HDS) towards sulfur compounds rather than towards olefins, thus preserving the octane number of the fuel while highly reducing the sulfur content and, thus, the possibility of air pollution with sulfur oxides. A similar performance enhancement was obtained in ODS, where the high dispersion of WO3 (due to the use of ILs during the synthesis) allows for noteworthy results at very low temperatures (50â—¦ C)
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
A novel role for the Receptor for Advanced Glycation End-products in neural progenitor cells derived from adult SubVentricular Zone
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