Degradation of superconductivity and spin fluctuations by electron over-doping in LaFeAsO$_{1-x}$F$_{x}$

TL;DR

This study investigates how electron over-doping in LaFeAsO$_{1-x}$F$_{x}$ suppresses superconductivity and spin fluctuations, highlighting the importance of spin dynamics in the superconducting mechanism.

Contribution

It provides experimental evidence linking the suppression of spin fluctuations to the decline of superconductivity in over-doped LaFeAsO$_{1-x}$F$_{x}$, supporting theories of spin fluctuation-mediated pairing.

Findings

Spin fluctuations are present in superconducting samples.

Spin fluctuations are suppressed in heavily over-doped, non-superconducting samples.

Results support the role of spin fluctuations in superconductivity.

Abstract

Low energy spin fluctuations are studied for the electron-doped Fe-based superconductor LaFeAsO(1-x)F(x) by inelastic neutron scattering up to the energy transfer of w = 15 meV using polycrystalline samples. Superconducting samples (x=0.057, Tc=25 K and x=0.082, Tc=29 K) show dynamical spin susceptibility chi"(w) almost comparable with the parent sample's. However chi"(w) is almost vanished in the x=0.158 sample where the superconductivity is highly suppressed. These results are compatible with the theoretical suggestions that the spin fluctuation plays an important role for the superconductivity.