75As-NQR and57Fe-NMR Studies on Heavily Overdoped LaFeAsO-Based Superconductors

Abstract

We report 75 As-nuclear quadrupole resonance (NQR) and 57 Fe-nuclear magnetic resonance (NMR) studies on heavily electron-doped LaFeAsO-based compounds with T c =5 and 8 K. The high quality of the samples was ensured by both narrow 57 Fe-NMR and 75 As-NQR spectra despite in the heavily overdoped state. Nuclear spin relaxation rate (1/ T 1 ) measurements by 75 As-NQR at zero field has revealed that a coherence peak just below T c partially recovers in heavily electron-overdoped regimes where the nesting condition of hole and electron Fermi surfaces (FSs) becomes significantly worse. This result suggests that the interband scattering between the hole and electron FSs is suppressed by the heavily electron-overdoping because the hole FSs become smaller.