Signature of multigap nodeless superconductivity in fluorine-doped NdFeAsO

TL;DR

This study reveals multigap nodeless superconductivity in fluorine-doped NdFeAsO through analysis of the lower critical field, supporting a two-band s-wave model and confirming the nodeless nature of the energy gap.

Contribution

First experimental evidence of multigap nodeless superconductivity in fluorine-doped NdFeAsO using $H_{c1}(T)$ measurements and two-band modeling.

Findings

Pronounced changes in $H_{c1}(T)$ curvature indicate multiband effects.

Data fits well with a two-band $s$-wave model.

Superconducting gap is confirmed to be nodeless.

Abstract

We investigate the temperature dependence of the lower critical field $H_{c1}(T)$, the field at which vortices penetrate into the sample, of a high-quality fluorine-doped NdFeAsO single crystal under static magnetic fields $H$ parallel to the $c$-axis. The temperature dependence of the first vortex penetration field has been experimentally obtained and pronounced changes of the $H_{c1}$(T) curvature are observed, which is attributed to the multiband superconductivity. Using a two-band model with $s$-wave-like gaps, the temperature-dependence of the lower critical field $H_{c1}(T)$ can be well described. These observations clearly show that the superconducting energy gap in fluorine-doped NdFeAsO is nodeless. The values of the penetration depth at $T$ = 0\,K have been determined and confirm that the pnictide superconductors obey an Uemura-style relationship between $T_{c}$ and $\lambda_{ab}(0)^{-2}$