  Using non-resonant Fe K-beta x-ray emission spectroscopy, we reveal that
Sr-doping of 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 the superconducting critical temperature with pressure lends
support to theories for superconductivity involving unconventional pairing
mediated by magnetic fluctuations.
