Competition/Coexisitence of Magnetism and Superconductivity in Iron Pnictides Probed by Muon Spin Rotation

Abstract

The presence of macroscopic phase separation into superconducting and magnetic phases in LaFeAsO${}_{1-x}$F${}_x$ (LFAOF) and CaFe${}_{1-x}$Co${}_x$AsF (CFCAF) is demonstrated by muon spin rotation (muSR) measurement across their phase boundaries ($x=0.06$ for LFAOF and $x=0.075$--0.15 for CFCAF). In LFAOF, both magnetism and superconductivity develop simultaneously below a common critical temperature, $T_m=T_c=18$ K, where the magnetism is characterized by strong randomness. A similar, but more distinct segregation of these two phases is observed in CFCAF, where the magnetic phase retains $T_m$ as close to that of the parent compound ($T_c<<T_m=80$--120 K) and the superconducting volume fraction is proportional to the Co content $x$. The close relationship between magnetism and superconductivity is discussed based on these experimental observations. Concerning superconducting phase, an assessment is made on the anisotropy of order parameter in the superconducting state of LFAOF, CFCAF, and Ba${}_{1-x}$K${}_x$Fe${}_2$As${}_2$ (BKFA, $x=0.4$) based on the temperature dependence of superfluid density [$n_s(T)$] measured by muSR. The gap parameter, $2\Delta /k_B{T}_c$, determined from $n_s(T)$ exhibits a tendency that hole-doped pnictides (BKFA) is much greater than those in electron-doped ones (LFAOF, CFCAF), suggesting difference in the coupling to bosons mediating the Cooper pairs between relevant $d$ electron bands.

20 pages, 11 figures

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Cited by in corpus (9)

• Homogeneous vs. inhomogeneous coexistence of magnetic order and superconductivity probed by NMR in Co and K doped iron pnictides
• Presure-Induced Superconducting State of Antiferromagnetic CaFe${}_2$As${}_2$
• Effects of cobalt doping and three-dimensionality in $BaF{e}_{2}A{s}_2$
• Superfluid Density and Field-Induced Magnetism in Ba(Fe1-xCox)2As2 and Sr(Fe1-xCox)2As2 Measured with Muon Spin Relaxation
• Pseudogap-less high T${}_c$ superconductivity in BaCo${}_x$Fe${}_{2-x}$As${}_2$
• Superfluid density and superconducting gaps of RbFe_{2}As_{2} as a function of hydrostatic pressure
• Superconducting gap structure in ambient-pressure-grown $\mathrm{La}{\mathrm{O}}_{0.5}{\mathrm{F}}_{0.5}\mathrm{Bi}{\mathrm{S}}_2$
• Homogeneous coexistence of SDW and SC states in CaFe(1-x)Co(x)AsF studied by nuclear magnetic resonance
• Interplay of magnetism and superconductivity in 2D extended Hubbard model