Magnetic torque analysis including vortex core contributions for Ba(Fe,Co)2As2 single crystal

Abstract

Superconducting torque measurements for a Ba(Fe,Co)2As2 iron arsenic superconductor have been carried out to obtain anisotropy in 1kG at 10K as well as in 10kG at 22K. We found that the anisotropy in penetration depth γλ and the anisotropy in coherence length γξ in the multi-band Kogan analysis are modest or almost isotropic. Theoretical calculation suggests the anisotropy of carrier mass γλ is approximated as 3 in BaFe2As2 system. The γλ value changes from 1 to 3 obtained by the torque analyses, and is in good agreement with the theoretical prediction. The torque curve was also analyzed by our new torque theory, which takes into account the vortex core contribution properly. We conclude that our Ba(Fe,Co)2As2 single crystal is almost isotropic in marked contrast with high-Tc cuprates.