(Ca,Sr)Fe2As2-XES

Using non-resonant Fe Kβ x-ray emission spectroscopy, we reveal that Sr substitution into CaFe₂As₂ decouples the Fe moment from the volume collapse transition, yielding a collapsed-tetragonal, paramagnetic normal state out of which superconductivity develops. X-ray diffraction measurements implicate the c-axis lattice parameter as the controlling criterion for the Fe moment, promoting a generic description for the appearance of pressure- induced superconductivity in the alkaline-earth-based 122 ferropnictides (AFe₂As₂). The evolution of T_c with pressure lends support to theories for superconductivity involving unconventional pairing mediated by magnetic fluctuations. This work appeared in Physical Review B 90, 144506 (2014).