Field and Temperature Dependence of the Superfluid Density in LaO_{1-x}F_xFeAs Superconductors: A Muon Spin Relaxation Study

TL;DR

This study investigates the superfluid density in LaO_{1-x}F_xFeAs superconductors using muon spin relaxation, revealing temperature and field dependencies that suggest unconventional superconductivity and providing key penetration depth measurements.

Contribution

First muSR study on LaO_{1-x}F_xFeAs showing temperature and field dependence of superfluid density and evidence for unconventional pairing mechanisms.

Findings

Superfluid density shows temperature dependence consistent with weak coupling BCS or dirty d-wave.

Field dependence indicates unconventional superconductivity.

Penetration depths are 254 nm and 364 nm for different doping levels.

Abstract

We present zero field and transverse field \muSR experiments on the recently discovered electron doped Fe-based superconductor LaO_{1-x}F_xFeAs. The zero field experiments on underdoped (x=0.075) and optimally doped (x=0.1) samples rule out any static magnetic order above 1.6 K in these superconducting samples. From transverse field experiments in the vortex phase we deduce the temperature and field dependence of the superfluid density. Whereas the temperature dependence is consistent with a weak coupling BCS s-wave or a dirty d-wave gap function scenario, the field dependence strongly evidences unconventional superconductivity. We obtain the in-plane penetration depth of \lambda_{ab} (0) = 254(2)nm for LaO_{0.9}F_{0.1}FeAs and \lambda_{ab} (0) = 364(8)nm for LaO_{0.925}F_{0.075}FeAs. Further evidence for unconventional superconductivity is provided by the ratio of T_c versus the superfluid density, which is close to the Uemura line of hole doped high-T_c cuprates.