Regensburg 2007 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 22: Low-dimensional Systems - Materials

TT 22.8: Vortrag

Donnerstag, 29. März 2007, 11:30–11:45, H18

Orbital Ordering in Cs₂AgF₄ - an electronic structure study — •Deepa Kasinathan¹, Klaus Koepernik^1,2, and Helge Rosner¹ — ¹Max Planck Institute for Chemical Physics of Solids, Dresden, Germany — ²IFW Dresden, P.O. Box 270016, D-01171, Germany

The argentate Cs₂AgF₄, first synthesized in 1974 has many similarities to the high-T_c cuprates, featuring AgF₂ sheets in place of CuO₂ sheets. While the undoped cuprates are antiferromagnetic, this argentate is ferromagnetic with a T_Curie of about 15 K. Density functional calculations in the proposed tetragonal structure produce an itenerant half-metallic ferromagnet. Recent inelastic neutron scattering experiments have suggested an orthorhombic structure that allows an orbitally ordered ferromagnetic ground state. We performed electronic structure calculations using the LDA+U method on this system and were able to obtain an orbitally ordered ground state, not only for the newly proposed orthorhombic lattice but also for the orginal tetragonal lattice by constraining the bravais lattice and allowing the change of the atomic basis. In specific, very small changes in the position of the in-plane fluorine atoms already trigger an orbital ordering. Our calculated energy scale shows that this orbitally ordered state should be stable for all temperatures, consistent with the experiment.