Microwave Surface Impedance Measurements of the Electronic State and Dissipation of Magnetic Vortices in Superconducting Iron-Based LiFeAs Single Crystals

摘要

LiFeAs is one of the iron-based superconductors having multiple gaps with thepossible sign reversal. To clarify how those novel natures affect the energydissipation of magnetic vortices, we investigated the microwave surfaceimpedance of LiFeAs single crystals under finite magnetic fields. The flux-flowresistivity enhanced rapidly at low magnetic fields, which is similar to thecase of MgB$_{2}$. This is probably the consequence of the multiple-gap natureand the gap anisotropy. This suggest that the sign-reversal is not importantfor the flux-flow even for multiple-gap superconductors. As for the electronicstate, the vortex core of LiFeAs turned out to be "moderately clean".Furthermore, the mean free path inside the vortex core was much shorter thanthat outside, and was close to the core radius. These results strongly suggesta process specific to the core boundary is important for a scattering mechanisminside the vortex core.