Microwave surface-impedance measurements of the electronic state and dissipation of magnetic vortices in superconducting LiFeAs single crystals

Abstract

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 MgB2. This is probably the consequence of the multiple-gap nature and the gap anisotoropy. 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.

Vortex motion and flux-flow resistivity in dirty multiband superconductors

“…Several recent experiments [1][2][3][4][5][6] confirm that behaviour. For MgB 2 we have obtained a quantitative agreement with experimental results 6 choosing the ratio of diffusivities in two bands D 2 /D 1 = 2.5.…”

“…In strong magnetic fields H c2 − B H c2 the motion of dense vortex lattices has been extensively studied with the help of linear response theory [11][12][13] . In these works the slope of flux-flow resistivity S = (H c2 /ρ n )(dρ f /dB) (2) has been shown to have a universal temperature dependence in the dirty limit. It is characterized by a monotonic increase from S(T = 0) = 1.72 to S(T = T c ) = 5 12 .…”

“…Recent transport experiments reveal quite unusual behaviour of the flux-flow resistive states in multiband superconductors [1][2][3][4][5][6] . The magnetic field dependencies of flux-flow resistivity ρ f (B) were found to be qualitatively different from that observed in single-band superconductors 7 .…”

“…At small d the critical field is determined by the second band which has the smallest diffusivity H c2 = H (2) c2 . Then with increasing d the superconductivity changes the host band so that H c2 = H (1) c2 .…”

Low-temperature-compatible tunneling-current-assisted scanning microwave microscope utilizing a rigid coaxial resonator

“…In fact, cryogenic SMM has revealed that intrinsic inhomogeneity is related to the metal-insulator transition [19,20] and phase separation [21,22]. Additionally, SMM is expected to serve as a tool for locally studying inhomogeneous superconductors such as high-T c cuprate in the pseudogap phase [23,24] and vortex matter [25,26] because the microwave response directly reflects the low-energy quasiparticle dynamics [27,28].…”