  LiFeAs is one of the iron-based superconductors having multiple gaps with the
possible sign reversal. To clarify how those novel natures affect the energy
dissipation of magnetic vortices, we investigated the microwave surface
impedance of LiFeAs single crystals under finite magnetic fields. The flux-flow
resistivity enhanced rapidly at low magnetic fields, which is similar to the
case of MgB$_{2}$. This is probably the consequence of the multiple-gap nature
and the gap anisotropy. This suggest that the sign-reversal is not important
for the flux-flow even for multiple-gap superconductors. As for the electronic
state, the vortex core of LiFeAs turned out to be "moderately clean".
Furthermore, the mean free path inside the vortex core was much shorter than
that outside, and was close to the core radius. These results strongly suggest
a process specific to the core boundary is important for a scattering mechanism
inside the vortex core.
