Orbital orderings and optical conductivity in cs₂agf₄

The JahnTeller (JT) distortion induced orbital order and optical-conductivity in Cs₂AgF₄ are investigated by first-principle calculations. Cs₂AgF₄ contains 4d ⁹ Ag²⁺, similar to 3d⁹ Cu²⁺ of La₂CuO₄. Although Cs₂AgF₄ is an isoelectronic analogue of La₂CuO₄, their magnetisms are radically different: La₂CuO₄ is antiferromagnetism (AFM), while Cs₂AgF₄ is proposed to be ferromagnetism (FM) based on recent neutron scattering data. The great difference can be understood from the JT distortions in the AgF₆ octahedron, which favors the formation of staggered orbital order of dz²-x² and d z ²-y². Such orbital order favors FM state, according to GoodenoughKanamori Rules. We find when the JT distortion is larger than 0.03, the ground state of Cs₂AgF₄ is AFM. This antiferromagnetism might induce superconductivity, just as La ₂CuO₄. In order to confirm such orbital order of Ag, we present the calculated optical-conductivity, which could be examined by experiment.