Anisotropic superconducting properties of MgB₂ single crystals probed by in-plane electrical transport measurements

We report on the study of the electronic anisotropy of the MgB2 superconductor using the in-plane resistivity measurements in the magnetic field applied perpendicular and parallel to Mg and B planes of MgB₂ single crystals. The results show the temperature dependent anisotropy of the upper critical field with the anisotropy ratio γ = H_c2∥/H_c2⊥ increasing from 2.2 close to T_c up to about 3 below 30 K. Our estimation of the in-plane and out-of-plane coherence length of about ξ_ab(0) = 68 Å and ξ_c(0) = 23 Å and the electronic mean-free path l_ab = 240 ̊, and l_c = 60 ̊, respectively, indicates MgB₂ single crystal approaches the clean limit type-II superconductor.