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 ε_ξ. This allows for the extraction of ε_ξ at magnetic fields far below the upper critical field Bc2. We find that increasing the magnetic field decreases the anisotropy of the coherence length.