Coupled orthorhombic distortion, antiferromagnetism, and superconductivity in a single twin domain of Ba(Fe$_{\mathrm{1-x}}$Co$_{\mathrm{x}})_{2}$As$_{2}$ (x$=$0.047)*

The interplay between structure, magnetism, and superconductivity in single crystal Ba(Fe$_{\mathrm{1-x}}$Co$_{\mathrm{x}})_{2}$As$_{2}$ (x$=$0.047) has been studied using high-resolution X-ray diffraction by monitoring charge Bragg peaks in each twin domain separately. The emergence of superconducting state is correlated with the suppression of theorthorhombic distortion around $T_{C}$, exhibiting the competition between orthorhombicity and superconductivity. Above $T_{S}$, the Bragg peak widths gradually broaden, possibly induced by orthorhombic (nematic) fluctuations in the paramagnetic tetragonal phase. Upon cooling, anomalies in the peak width are observed at $T_{S}$ and also $T_{N}$ indicative of strong magnetoelastic coupling. Using the capability to study individual twin domains, the peak widths in the \textit{ab}-plane are found to exhibit anisotropic behavior along and perpendicular to the stripe-type AFM wave vector. In contrast, the temperature dependencies of the out-of-plane peak width showan anomaly at $T_{N}$, reflecting the connection between Fe-As distance and Fe local moment.