Nodeless two-gap superconductivity in stoichiometric iron pnictide LiFeAs

TL;DR

This study investigates the superconducting properties of LiFeAs, revealing nodeless two-gap superconductivity and the influence of pairbreaking scattering, contributing to understanding the evolution of the superconducting gap in iron pnictides.

Contribution

It provides experimental evidence for nodeless two-gap superconductivity in LiFeAs and highlights the role of pairbreaking scattering in gap behavior deviations.

Findings

Superfluid density fits a two-gap model

Superconducting gap evolves from nodeless to nodal with doping

Pairbreaking scattering affects low-temperature behavior

Abstract

The variations of in- and inter- plane London penetration depths, $\Delta\lambda(T)$, were measured using a tunnel diode resonator in single crystals of the intrinsic pnictide superconductor LiFeAs. This compound appears to be in the clean limit with a residual resistivity of 4 ($T\to0$) to 8 ($T_c$) $\mu \Omega\cdot$cm and $RRR$ of 65 to 35, respectively. The superfluid density, $\rho_s(T)=\lambda^2(0)/\lambda^2(T)$, is well described by the self-consistent two-gap $\gamma-$model. Together with the previous data, our results support the universal evolution of the superconducting gap from nodeless to nodal upon departure from optimal doping. We also conclude that pairbreaking scattering plays an important role in the deviation of the low-temperature behavior of $\lambda(T)$ from exponential in Fe-based compounds.