66 research outputs found

    Impact of the Spin Density Wave Order on the Superconducting Gap of Ba(Fe1−x_{1-x}Cox_x)2_2As2_2

    Full text link
    We report a doping dependent electronic Raman scattering measurements on iron-pnictide superconductor Ba(Fe1−x_{1-x}Cox_x)2_2As2_2 single crystals. A strongly anisotropic gap is found at optimal doping for x=0.065 with Δmax∼5Δmin\Delta_{max}\sim 5\Delta_{min}. Upon entering the coexistence region between superconducting (SC) and spin-density-wave (SDW) orders, the effective pairing energy scale is strongly reduced. Our results are interpreted in terms of a competition between SC and SDW orders for electronic state at the Fermi level. Our findings advocate for a strong connection between the SC and SDW gaps anisotropies which are both linked to interband interactions.Comment: 4 pages, 3 figure

    Spin-Density-Wave Gap with Dirac Nodes and Two-Magnon Raman Scattering in BaFe2As2

    Full text link
    Raman selection rules for electronic and magnetic excitations in BaFe2As2 were theoretically investigated and applied them to the separate detection of the nodal and anti-nodal gap excitations at the spin density wave (SDW) transition and the separate detection of the nearest and the next nearest neighbor exchange interaction energies. The SDW gap has Dirac nodes, because many orbitals participate in the electronic states near the Fermi energy. Using a two-orbital band model the electronic excitations near the Dirac node and the anti-node are found to have different symmetries. Applying the symmetry difference to Raman scattering the nodal and anti-nodal electronic excitations are separately obtained. The low-energy spectra from the anti-nodal region have critical fluctuation just above TSDW and change into the gap structure by the first order transition at TSDW, while those from the nodal region gradually change into the SDW state. The selection rule for two-magnon scattering from the stripe spin structure was obtained. Applying it to the two-magnon Raman spectra it is found that the magnetic exchange interaction energies are not presented by the short-range superexchange model, but the second derivative of the total energy of the stripe spin structure with respect to the moment directions. The selection rule and the peak energy are expressed by the two-magnon scattering process in an insulator, but the large spectral weight above twice the maximum spin wave energy is difficult to explain by the decayed spin wave. It may be explained by the electronic scattering of itinerant carriers with the magnetic self-energy in the localized spin picture or the particle-hole excitation model in the itinerant spin picture. The magnetic scattering spectra are compared to the insulating and metallic cuprate superconductors whose spins are believed to be localized.Comment: 38 pages, 11 figure

    Hippocampal-Dependent Spatial Memory in the Water Maze is Preserved in an Experimental Model of Temporal Lobe Epilepsy in Rats

    Get PDF
    Cognitive impairment is a major concern in temporal lobe epilepsy (TLE). While different experimental models have been used to characterize TLE-related cognitive deficits, little is known on whether a particular deficit is more associated with the underlying brain injuries than with the epileptic condition per se. Here, we look at the relationship between the pattern of brain damage and spatial memory deficits in two chronic models of TLE (lithium-pilocarpine, LIP and kainic acid, KA) from two different rat strains (Wistar and Sprague-Dawley) using the Morris water maze and the elevated plus maze in combination with MRI imaging and post-morten neuronal immunostaining. We found fundamental differences between LIP- and KA-treated epileptic rats regarding spatial memory deficits and anxiety. LIP-treated animals from both strains showed significant impairment in the acquisition and retention of spatial memory, and were unable to learn a cued version of the task. In contrast, KA-treated rats were differently affected. Sprague-Dawley KA-treated rats learned less efficiently than Wistar KA-treated animals, which performed similar to control rats in the acquisition and in a probe trial testing for spatial memory. Different anxiety levels and the extension of brain lesions affecting the hippocampus and the amydgala concur with spatial memory deficits observed in epileptic rats. Hence, our results suggest that hippocampal-dependent spatial memory is not necessarily affected in TLE and that comorbidity between spatial deficits and anxiety is more related with the underlying brain lesions than with the epileptic condition per se

    Disability Policies in France: Changes and Tensions between the Category-based, Universalist and Personalized Approaches

    Get PDF
    In this article, the authors show that the current French disability policy is traversed by conflicts between three different approaches to disability which came about at different periods in history. They begin by looking at the origins of disability policy in France. This policy was developed during the 20th century, from notions of repair, indemnification and compensation through rehabilitation. It became institutionalized in 1975, when two laws were passed, giving it the form of a category-based policy. Between 1970 and 2000, affected by the international situation, this policy came into conflict with a universalist policy. More recently there has been a desire to develop a personalized approach. Finally, the authors use two examples (taken from recent debates on the implementation in France of the new law of 11 February 2005) to show the tensions that have led to the coexistence of these three approaches within current disability policy
    • …
    corecore