Probing nematicity and magnetism with combined tunable strain and x-ray scattering/fluorescence techniques

In this talk I will review our recent progress at the Advanced Photon Source in combining in situ tunable uniaxial stress with simultaneous transport measurements and several synchrotron x-ray techniques to perform unique characterizations of several iron-based superconductors. In Co-doped BaFe₂As₂ we use x-ray diffraction (XRD) to carefully monitor the strain detwinning of the orthorhombic structural domains and make a precise determination of the spontaneous resistivity anisotropy across temperature within the nematic phase. In EuFe₂As₂ we use x-ray magnetic circular dichroism (XMCD) to make the first observation of a magnetic field-induced spin flip transition of antiferromagnetic Eu moments in a strain-detwinned sample. In Co-doped EuFe₂As₂ we use XMCD to monitor the magnetic field-induced reorientation of ferromagnetic Eu moments from out of plane to in-plane, which we correlate with a strain-tunable field-induced superconductivity. Finally, in FeSe we combine XRD and x-ray linear dichroism (XLD) to observe the nematic orbital polarization anisotropy within the nematic phase across a range of strain and detwinning values. This unique combination of tuning and probing techniques has so far given new insight into these interesting materials and presents a new approach to answering unresolved questions in iron-based superconductors and beyond.