Miniature Hall-probe arrays were used to measure the critical current densities for the three main directions of vortex motion in the stoichiometric LiFeAs superconductor. These correspond to vortices oriented along the c-axis moving parallel to the ab-plane, and to vortices in the ab-plane moving perpendicular to, and within the plane, respectively. The measurements were carried out in the low-field regime of strong vortex pinning, in which the critical current anisotropy is solely determined by the coherence length anisotropy parameter, { \epsilon}_{ \xi}. This allows extraction of { \epsilon}_{ \xi} at magnetic fields far below the upper critical field B_c2. We find that increasing magnetic field decreases the anisotropy of the coherence length.
Categories: cond-mat.supr-con