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

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.

11 pages, 2 figures, 2 tables

References in corpus (3)

• Magnetic Order versus superconductivity in the Iron-based layered La(O1-xFx)FeAs systems
• Superconductivity at 43 K in Samarium-arsenide Oxides $SmFeAs{O}_{1-x}{F}_x$
• Very High Field Two-Band Superconductivity in LaFeAsO_0.89F_0.11

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• Nuclear magnetic relaxation and superfluid density in Fe-pnictide superconductors: An anisotropic \pm s-wave scenario
• Enhancement of Superfluid Stiffness, Suppression of Superconducting T_c and Field-induced Magnetism in the Pnictide Superconductor LiFeAs
• Evidence for multiple gaps in specific heat of LiFeAs crystals
• Insular superconductivity in Co-doped iron pnictide CaFe${}_{1-x}$Co${}_x$AsF
• Full Gap Superconductivity in Ba${}_{0.6}$K${}_{0.4}$Fe${}_2$As${}_2$ Probed by Muon Spin Rotation
• Systematic ^{75}As NMR study of the dependence of low-lying excitations on F doping in the iron oxypnictide LaFeAs(O_{1-x}F_{x})
• Competition/Coexisitence of Magnetism and Superconductivity in Iron Pnictides Probed by Muon Spin Rotation
• Determination of characteristic muon precession and relaxation signals in FeAs and FeAs2, possible impurity phases in pnictide superconductors