^{75}As NMR study of the growth of paramagnetic-metal domains due to electron doping near the superconducting phase in LaFeAsO_{1-x}F_{x}

TL;DR

This study uses NMR to investigate how electron doping influences the growth of paramagnetic-metal domains near the superconducting transition in LaFeAsO_{1-x}F_{x}, revealing new insights into phase segregation.

Contribution

It provides evidence of PM domain growth linked to doping and pressure, challenging existing paradigms and supporting orbital fluctuation theory in high-T_c pnictides.

Findings

PM domains grow with doping and pressure

Superconductivity correlates with PM domain expansion

Existence of PM domains supports ferroquadrupole state

Abstract

We studied the electric and magnetic behavior near the phase boundary between antiferromagnetic (AF) and superconducting (SC) phases for a prototype of high-T_c pnictides LaFeAsO_{1-x}F_{x} by using nuclear magnetic resonance, and found that paramagnetic-metal (PM) domains segregate from AF domains. PM domains grow in size with increasing electron doping level and are accompanied by the onset of superconductivity, and thus application of pressure or increasing the doping level causes superconductivity. The existence of PM domains cannot be explained by the existing paradigm that focuses only on the relationship between superconductivity and antiferromagnetism. Based on orbital fluctuation theory, the existence of PM domains is evidence of the ferroquadrupole state.