No anomalous spin fluctuation in optimally doped and overdoped iron-based oxypnictide superconductors LaFeAsO$_{1-x}$F$_x$ probed by muon spin relaxation

TL;DR

This study used muon spin relaxation to investigate magnetic fluctuations in optimally doped and overdoped LaFeAsO$_{1-x}$F$_x$ superconductors, finding no evidence of magnetic fluctuation within the muons' time window.

Contribution

It provides the first muon spin relaxation measurements showing no magnetic fluctuation in these superconductors, suggesting other factors like multiband effects are key to pairing.

Findings

No magnetic fluctuation detected in muon time window

Magnetic fluctuations observed by neutron scattering are not present in muon measurements

Multiband effects may be crucial for superconductivity

Abstract

Zero field and longitudinal field muon spin relaxation measurements have been performed in optimally doped and overdoped superconductors LaFeAsO$_{1-x}$F$_x$ in order to investigate the magnetic fluctuation over a wide range of temperature and longitudinal field. We have observed no sign of magnetic fluctuation against temperature in the muons' time window (10$^{-5}\sim$ 10$^{-9}$s). Considering the current results and other results, i.e., spin fluctuation observed by neutron scattering, pseudogap-like behaviors by NMR and photoemission spectroscopy, it is suggested that not only the spin fluctuation but also the multiband character with several different orbital contributions at the Fermi surface may play an important role in the superconducting pairing mechanism of LaFeAsO$_{1-x}$F$_x$.