  Recent investigations of the superconducting iron-arsenide families have
highlighted the role of pressure, be it chemical or mechanical, in fostering
superconductivity. Here we report that CaFe2As2 undergoes a pressure-induced
transition to a non-magnetic, volume "collapsed" tetragonal phase, which
becomes superconducting at lower temperature. Spin-polarized total-energy
calculations on the collapsed structure reveal that the magnetic Fe moment
itself collapses, consistent with the absence of magnetic order in neutron
diffraction.
