Coexistence of Supercondcutivity and Magnetism in LaFeAs(O0.94F0.06) Probed by Muon Spin Relaxation

TL;DR

This study uses muon spin relaxation to reveal that LaFeAs(O0.94F0.06) exhibits phase separation into magnetic and superconducting regions near the phase boundary, indicating a close relationship between magnetism and superconductivity.

Contribution

It provides experimental evidence of coexistence and phase separation of magnetism and superconductivity in LaFeAs(O0.94F0.06), highlighting their interplay near the phase boundary.

Findings

Phase separation into magnetic and superconducting phases occurs at x=0.06.

Both phases develop below a common Tc of approximately 18 K.

Magnetism and superconductivity coexist near the phase boundary, suggesting a close relationship.

Abstract

Recent discovery of oxypnictide superconductor LaFeAs(O,F) (LFAO-F) with the critical temperature (Tc) of 26 K and succeeding revelation of much increased Tc upon substitution of La for other rare earth elements (such as Sm, leading to ~43 K) and application of pressure for LFAO-F (~ 43 K) has triggered broad interest in the mechanism yielding relatively high Tc in this new class of compounds. While they share a feature with high-Tc cuprates that superconductivity occurs upon carrier doping to pristine compound which exhibits magnetism, they also resemble the heavy-fermion compounds in the sense that superconductivity appears in the vicinity of magnetic phase. Investigation of electronic states near the boundary between these two phases might provide some useful information on the mechanism of superconductivity, as it has been proved to be the case in many exotic superconductors. Here we show by muon experiment in the LFAO-F compound that a macroscopic phase separation into superconducting and spin glass-like magnetic phases occurs at x=0.06 that is near the phase boundary, where both the magnetism and superconductivity develop simultaneously below a common Tc ~ 18 K. This accordance strongly suggests intimate relationship between magnetism and superconductivity typically found in heavy-fermion systems near the quantum critical point.