Anisotropy of the coherence length from critical currents in the stoichiometric superconductor LiFeAs

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 vortex lines along the c axis moving parallel to the ab plane, and to vortex lines 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 _ξ. This allows for the extraction of _ξ at magnetic fields far below the upper critical field B _c2. We find that increasing the magnetic field decreases the anisotropy of the coherence length.