Abstract
The Jahn–Teller (JT) distortion induced orbital order and optical-conductivity in Cs2AgF4are investigated by first-principle calculations. Cs2AgF4contains 4d9Ag2+, similar to 3d9Cu2+of La2CuO4. Although Cs2AgF4is an isoelectronic analogue of La2CuO4, their magnetisms are radically different: La2CuO4is antiferromagnetism (AFM), while Cs2AgF4is proposed to be ferromagnetism (FM) based on recent neutron scattering data. The great difference can be understood from the JT distortions in the AgF6octahedron, which favors the formation of staggered orbital order of dz2-x2and dz2-y2. Such orbital order favors FM state, according to Goodenough–Kanamori Rules. We find when the JT distortion is larger than 0.03, the ground state of Cs2AgF4is AFM. This antiferromagnetism might induce superconductivity, just as La2CuO4. In order to confirm such orbital order of Ag , we present the calculated optical-conductivity, which could be examined by experiment.
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