Microwave Surface Impedance Measurements of LiFeAs Single Crystals

TL;DR

This study uses microwave surface impedance measurements to reveal that LiFeAs is a multi-gap, nodeless superconductor with enhanced quasiparticle relaxation below its critical temperature, providing insights into its superconducting properties.

Contribution

It presents the first microwave impedance analysis of LiFeAs, demonstrating its multi-gap, nodeless superconductivity and quasiparticle dynamics.

Findings

LiFeAs has a nodeless superconducting gap.

LiFeAs exhibits multiple isotropic gaps.

Quasiparticle relaxation time increases rapidly below T_c.

Abstract

We report results of microwave surface impedance measurements of LiFeAs single crystals. The in-plane penetration depth depends on temperature exponentially at low temperatures, which strongly suggests that this material has the nodeless superconducting gap. The temperature dependence of the superfluid density indicates that LiFeAs is a multi-gap superconductor with at least two isotropic gaps. In addtion, the real part of the microwave conductivity exhibits a large enhancement below $T_\mathrm{c}$, indicating that the quasi-particle relaxation time, $\tau$, increases rapidly below $T_\mathrm{c}$. We believe that this enhancement is rather common to all superconductors where an inelastic scattering is dominant above $T_\mathrm{c}$, irrespective of the strength of the electron correlation.