Hidden Charge Order in an Iron Oxide Square-Lattice Compound
Hidden Charge Order in an Iron Oxide Square-Lattice Compound
Since the discovery of charge disproportionation in the ${\mathrm{FeO}}_{2}$ square-lattice compound ${\mathrm{Sr}}_{3}{\mathrm{Fe}}_{2}{\mathrm{O}}_{7}$ by M\"ossbauer spectroscopy more than fifty years ago, the spatial ordering pattern of the disproportionated charges has remained ``hidden'' to conventional diffraction probes, despite numerous x-ray and neutron scattering studies. We have used neutron Larmor diffraction and Fe …