Absence of large nanoscale electronic inhomogeneities in the Ba(Fe1-xCox)2As2 pnictide

75As NMR and susceptiblity were measured in a Ba(Fe1-xCox)2As2 single crystal for x=6% for various field H values and orientations. The sharpness of the superconducting and magnetic transitions demonstrates a homogeneity of the Co doping x better than +-0.25%. On the nanometer scale, the paramagnetic part of the NMR spectra is found very anisotropic and very narrow for H//ab which allows to rule out the interpretation of Ref.[6] in terms of strong Co induced electronic inhomogeneities. We propose that a distribution of hyperfine couplings and chemical shifts due to the Co effect on its nearest As explains the observed linewidths and relaxations. All these measurements show that Co substitution induces a very homogeneous electronic doping in BaFe2As2, from nano to micrometer lengthscales, on the contrary to the K doping.Comment: 6 pages, 4 figure

First-Principles Studies in Fe-Based Superconductors

[[abstract]]The discovery of high-temperature superconductivity in iron-based superconductors [1] has attracted intense recent research attention, especially given that these compounds contain no Cu atoms in comparison with the extensively studied cuprate families, the well-known high-temperature superconductors [2]. Similar to that in cuprate families, these systems show close proximity of superconductivity to the magnetic phase, and therefore the intimate relationship between these two seemingly exclusive phases is of great interest [3–15].[[notice]]補正完

Measurement of the higher-order anisotropic flow coefficients for identified hadrons in Au++Au collisions at sNN\sqrt{s_{_{NN}}} = 200 GeV

International audienceMeasurements of the anisotropic flow coefficients v2{Ψ2},v3{Ψ3},v4{Ψ4}, and v4{Ψ2} for identified particles (π±,K±, and p+p¯) at midrapidity, obtained relative to the event planes Ψm at forward rapidities in Au + Au collisions at sNN=200GeV, are presented as a function of collision centrality and particle transverse momenta pT. The vn coefficients show characteristic patterns consistent with hydrodynamical expansion of the matter produced in the collisions. For each harmonic n, a modified valence quark-number Nq scaling [plotting vn{Ψm}/(Nq)n/2 versus transverse kinetic energies (KET)/Nq] is observed to yield a single curve for all the measured particle species for a broad range of KET. A simultaneous blast-wave model fit to the observed vn{Ψm}(pT) coefficients and published particle spectra identifies radial flow anisotropies ρn{Ψm} and spatial eccentricities sn{Ψm} at freeze-out. These are generally smaller than the initial-state participant-plane geometric eccentricities ɛn{ΨmPP} as also observed in the final eccentricity from quantum interferometry measurements with respect to the event plane