Persistent Fe Moments In The Normal-State Collapsed-Tetragonal Phase Of The Pressure-Induced Superconductor Ca0.67sr0.33fe2as2

Using nonresonant Fe K beta 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 (AFe(2)As(2)). The evolution of T-c with pressure lends support to theories for superconductivity involving unconventional pairing mediated by magnetic fluctuations.