Upper critical field study of a LiFeAs single crystal grown by Sn flux

Temperaturedependence of the upper critical fields $H_{c2}(T)$ was investigated in a LiFeAs single crystal by measuring resistivity at a fixed magnetic field up to 36 T. $H_{c2}^{ab}$(0) and $H_{c2}^{ab}$ (0) values are obtained as 30 and 17.2 T respectively. $H_{c2}^{ab}$(0) is lower than expected one from the orbital limiting field $H_{c2}^{orb}$(0) because of the presence of a moderate Pauli limiting effect; upon fitting $H_{c2}^{ab}(T)$ with the WHH formula, the Maki parameter \textit{$\alpha $} = 0.65. For $H_{c2}^{c }$(T), rather a linearly increasing behavior of $H_{c2}(T)$ could be explained by a two-band model in a dirty limit. The anisotropy $H_{c2}^{ab}$ /$ H_{c2}^{c}$ ($T)$ is $\sim $2.3 near $T_{c }$and decreases with temperature being lowered to reaches $\sim $1.3 at $T$ = 0. We also compare $H_{c2}$ (T) of this 111 system with those of other Fe-based superconductors and conclude that the moderateness of the spin-paramagnetic effect is related with rather a weak slope of $H_{c2}(T)$ near $T_{c}$, which is inversely proportional to the Fermi velocity and mean free path. Thus, the comparison of the slope of $H_{c2}$ supports that LiFeAs is located in a rather clean limit among the Fe-based superconductors.