Muon-spin rotation study of the in-plane magnetic penetration depth of FeSe_0.85: evidence for nodeless superconductivity

TL;DR

This study uses muon-spin rotation to investigate the magnetic penetration depth in FeSe_0.85, providing evidence that its superconducting gap is nodeless and compatible with multi-gap or anisotropic s-wave models.

Contribution

It presents the first muon-spin rotation measurements of mbda_{ab} in FeSe_0.85, demonstrating a nodeless superconducting gap and exploring its possible gap structures.

Findings

mbda_{ab}^{-2}(T) suggests no nodes in the gap

Data compatible with two-gap or anisotropic s-wave models

Superconducting gap in FeSe_0.85 is nodeless

Abstract

The in-plane magnetic penetration depth \lambda_{ab} of the iron selenide superconductor with the nominal composition FeSe_0.85 was studied by means of muon-spin rotation. The measurements of \lambda_{ab}^{-2}(T) are inconsistent with the presence of nodes in the gap as well as with a simple isotropic s-wave type of the order parameter, but can be equally well described within a two-gap (s+s) and an anisotropic s-wave gap picture. This implies that the superconducting energy gap in FeSe_0.85 contains no nodes.