Resistivity and upper critical field in KFe${}_2$As${}_2$ single crystals

Abstract

We report resistivity measurements performed on KFe${}_2$As${}_2$ single crystals down to $T$ = 0.3 K and in magnetic fields up to 17.5 T. The in-plane resistivity vs. $T$ curve has a convex shape down to $\sim$50 K and shows a $T^2$ dependence below $\sim$45 K. The ratio of the c-axis to in-plane resistivities is $\sim$10 at room temperature and $\sim$40 at 4.2 K. The superconducting upper critical field $B_{c2}(T)$ has been determined from the resistivity data: $B_{c2}^{ab}$(0) = 4.47 T and $B_{c2}^c$(0) = 1.25 T. The anisotropy parameter $\hat{I}“$ = $B_{c2}^{ab}$ / $B_{c2}^c$ 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.

After minor revision, accepted for publication in J. Phys. Soc. Jpn