Microwave absorption in YBa[2]Cu[3]O[7-delta]-manganite superlattices

3 pages Erreur sur l'affiliation : CEA/DSM/IRAMIS et non CEA/DSM/DRECAMInternational audienceWe report on results of direct microwave absorption measurements of Re1−x Bx MnO3 /YBa2 Cu3 O7−δ half metal/d-wave superconductor superlattices (where Re - La and Pr) and (B - Sr and Ca) for microwave frequencies in the range from 9 to 20 GHz. The measurements of the entire heterostructure were performed mostly at temperatures below the superconducting transition. The obtained results strongly depend on the microwave frequency and can be qualitatively described within the theoretical model of high-frequency properties of Josephson junctions with a ferromagnetic barrier proposed by S. Takahashi, S. Hikino, M. Mori, J. Martinek, and S. Maekawa, Phys. Rev. Lett. 99, 057003 (2007)

In-plane field-induced vortex liquid correlations in underdoped Bi_2Sr_2CaCu_2O_8+\delta

The effect of a magnetic field component parallel to the superconducting layers on longitudinal Josephson plasma oscillations in the layered high temperature superconductor Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ is shown to depend on the thermodynamic state of the underlying vortex lattice. Whereas the parallel magnetic field component depresses the Josephson Plasma Resonance (JPR) frequency in the vortex solid phase, it may enhance it in the vortex liquid. There is a close correlation between the behavior of microwave absorption near the JPR frequency and the effectiveness of pancake vortex pinning, with the enhancement of the plasma resonance frequency occurring in the absence of pinning, at high temperature close to the vortex melting line. An interpretation is proposed in terms of the attraction between pancake vortices and Josephson vortices, apparently also present in the vortex liquid state.Comment: 8 pages, 7 Figures, submitted to Phys. Rev.

Electron irradiation of Co, Ni, and P-doped BaFe2As2 - type iron-based superconductors

17 pages, soumis pour publications dans les actes de M2S-2012International audienceHigh energy electron irradiation is used to controllably introduce atomic-scale point defects into single crystalline Ba(Fe_1-xCo_x)_2As_2, Ba(Fe_1-xNi_x)_2As_2, and BaFe_2(As_1-xP_x)_2. The appearance of the collective pinning contribution to the critical current density in BaFe_2(As_1-xP_x)_2, and the magnitude of its enhancement in Ba(Fe_1-xCo_x)_2As_2, conform with the hypothesis of quasi-particle scattering by Fe vacancies created by the irradiation. Whereas the insignificant modification of the temperature dependence of the superfluid density in Ba(Fe_1-xCo_x)_2As_2 and Ba(Fe_1-xNi_x)_2As_2 points to important native disorder present before the irradiation, the critical temperatures of these materials undergo a suppression equivalent to that observed in the much cleaner BaFe_2(As_1-xP_x)_2. This lends credence to the hypothesis of line nodes of the order parameter (at finite k_{z}) in the former two materials

Shear viscosity measurements at the vortex melting transition in confined geometry in optimally doped Bi2Sr2CaCu2O8

International audienceIn order to probe the vortex shear viscosity in the vortex liquid phase, we have introduced two types of vortex-confining structures in optimally doped Bi2Sr2CaCu2O8 single crystals. First, walls of strong vortex pinning separated by weakly pinning channels are fashioned by heavy ion irradiation through 25 um-thick Ni masks. Second, a low density of homogeneously distributed amorphous columnar defects is known to impose a polycrystalline structure to the vortex lattice. Resistivity measurements show that the inclusion of confining structures impede vortex flow in the liquid. The resistivity is remarkably well described by the Halperin-Nelson theory for the viscosity due to free two-dimensional vortex lattice dislocations

c-axis coupling in underdoped Bi(2)Sr(2)CaCu(2)O(8+δ) with varying degrees of disorder

c-axis coupling in underdoped Bi(2)Sr(2)CaCu(2)O(8+δ) with varying degrees of disorde

Disorder and cc-axis quasiparticle dynamics in underdoped Bi2Sr2CaCu2O8

Contribution à LT25International audienceWe present measurements of the Josephson plasma frequency and the in-plane penetration depth of underdoped single crystalline Bi2Sr2CaCu2O8 with varying degrees of disorder introduced by irradiation with 2.3 MeV electrons. Increasing disorder drives T_c down, in agreement with in all model descriptions of high T_c superconductivity. However, the manner in which the JPR frequency, the square of which represents the zero-frequency spectral weight of the c-axis conductivity in the superconducting state, is driven down by disorder depends more strongly on the model description. We show that only the model of impurity assisted quasiparticle hopping in a d-wave superconductor, together with strongly scattering point defects in the superconducting layers, can explain the disorder dependence of the c-axis plasma frequency, the in-plane penetration depth, and T_c consistently. From the data, we extract the energy scale governing nodal quasiparticle excitations, Delta_0 ~ 2.5 k_BT_c

Disorder and c-axis quasiparticle dynamics in underdoped Bi2Sr2CaCu2O8

Disorder and c-axis quasiparticle dynamics in underdoped Bi2Sr2CaCu2O