Multiband effects on the upper critical field angular dependence of 122-family iron pnictide superconductors

Detailed measurements of the in-plane resistivity were performed in a high-quality Ba(Fe1-xCox)2As2 (x=0.065) single crystal, in magnetic fields up to 9 T and with different orientations theta relative to the crystal c axis. A significant rho (T)H,theta rounding is observed just above the superconducting critical temperature Tc due to Cooper pairs created by superconducting fluctuations. These data are analyzed in terms of a generalization of the Aslamazov-Larkin approach, that extends its applicability to high reduced-temperatures and magnetic fields. This method allows us to carry out a criterion-independent determination of the angular dependence of the upper critical field, Hc2(theta). In spite of the relatively small anisotropy of this compound, it is found that Hc2(theta) presents a significant deviation from the single-band 3D anisotropic Ginzburg-Landau (3D-aGL) approach, particularly for large theta (typically above similar to 60o). These results are interpreted in terms of the multiband nature of these materials, in contrast with other proposals for similar Hc2(theta) anomalies. Our results are also consistent with an effective anisotropy factor almost temperature independent near Tc, a result that differs from the ones obtained by using a single-band model.

Automated summary

Detailed measurements were performed on a high-quality Ba(Fe1-xCox)2As2 (x=0.065) single crystal, revealing a significant rounding of the resistivity above the superconducting critical temperature Tc due to Cooper pairs. The analysis indicates that the angular dependence of the upper critical field, Hc2(theta), deviates significantly from the single-band model, particularly for large angles.