Resistivity and Upper Critical Field in KFe2As2 Single Crystals

We report resistivity measurements performed on KFe2As2 single crystals down to T = 0.3 K and in magnetic fields up to 17.5T. The in-plane resistivity vs T curve has a convex shape down to similar to 50 K and shows a T-2 dependence below similar to 45 K. The ratio of the c-axis to in-plane resistivities is similar to 10 at room temperature and similar to 40 at 4.2 K. The superconducting upper critical field B-c2(T) has been determined from the resistivity data: B-c2(ab)(0) = 4.47T and B-c2(c)(0) = 1.25 T. The anisotropy parameter Gamma = B-c2(ab)/B-c2(c) increases with T and is 6.8 at T = T-c. The strong curvature of the B-c2(ab)(T) curve indicates the existence of strong spin paramagnetic effects.