Magnetoelastic coupling and charge correlation lengths in a twin domain of Ba(Fe₁₋ₓCoₓ)₂As₂ (x=0.047): A high-resolution X-ray diffraction study

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The interplay between structure, magnetism and superconductivity in single crystal Ba(Fe₁₋ₓCoₓ)₂As₂ (x=0.047) has been studied using high-resolution X-ray diffraction by monitoring charge Bragg reflections in each twin domain separately. The emergence of the superconducting state is correlated with the suppression of the orthorhombic distortion around TC, exhibiting competition between orthorhombicity and superconductivity. Above Tₛ, the in-plane charge correlation length increases with the decrease of temperature, possibly induced by nematic fluctuations in the paramagnetic tetragonal phase. Upon cooling, anomalies in the in-plane charge correlation lengths along a (ξₐ) and b axes (ξb) are observed at Tₛ and also at Tₙ indicative of strong magnetoelastic coupling. The in-plane charge correlation lengths are found to exhibit anisotropic behavior along and perpendicular to the in-plane component of stripe-type AFM wave vector (101) O below around Tₙ. The temperature dependence of the out-of-plane charge correlation length shows a single anomaly at Tₙ, reflecting the connection between Fe-As distance and Fe local moment. The origin of the anisotropic in-plane charge correlation lengths ξₐ and ξb is discussed on the basis of the antiphase magnetic domains and their dynamic fluctuations.