Upper critical field and superconducting anisotropy of BaFe_2-xRu_xAs₂ (x=0.48 and 0.75) single crystals

The upper critical field (Hc2) was determined by applying a magnetic field along the ab plane and c axis for two single crystals of BaFe2-xRuxAs2 (x=0.48 and 0.75). The anisotropy of the Hc2(0), γ(0)=Hc2 ab(0)/Hc2 c(0), was ∼1.6 for x=0.48 and ∼2.3 for x=0.75. The angle-dependent resistance measured below Tc allowed perfect scaling features based on anisotropic Ginzburg-Landau theory, leading to consistent anisotropy values. Because only one fitting parameter γ is used in the scaling for each temperature, the validity of the γ value was compared with that determined from γ=Hc2 ab/Hc2 c. The γ obtained at a temperature close to Tc was 3.0 and decreased to 2.0 at low temperatures. Comparing to the anisotropy determined for electron- or hole-doped BaFe2As2 using the same method, the present results point to consistent anisotropy in Ru-doped BaFe2As2 with other electron- or hole-doped BaFe2As2.