Measurements of the superconducting fluctuations in optimally doped BaFe_2−xNi_xAs₂ under high magnetic fields: probing the 3D-anisotropic Ginzburg–Landau approach

The superconducting fluctuations well inside the normal state of Fe-based superconductors were experimentally studied through the in-plane paraconductivity in several high-quality, optimally doped BaFe_2−xNi_xAs₂ crystals. These measurements were performed in magnetic fields with amplitudes up to 14 T, and different orientations relative to the c-axis of the crystals (θ=0^∘, 53^∘, and 90^∘). The results allowed a stringent check of the applicability of a recently proposed Ginzburg–Landau approach for the fluctuating electrical conductivity of three-dimensional (3D) anisotropic materials in the presence of finite applied magnetic fields. (papers)