Electronic states and magnetic properties of edge-sharing Cu-O chains

The electronic states and magnetic properties for the copper oxides containing edge-sharing Cu-O chains such as Li₂CuO₂, La₆Ca₈Cu₂₄O₄₁, and CuGeO₃ are systematically studied. The optical conductivity σ(ω) and the temperature dependence of the magnetic susceptibility χ(T) for single-crystalline samples Li₂CuO₂ are measured as a reference system and analyzed by using the exact diagonalization method for small Cu-O clusters. It is shown that the spectral distribution of σ(ω) is different between edge-sharing and corner-sharing Cu-O-Cu bonds. The charge transfer gap in edge-sharing chains is larger than that of high-Tc cuprates. The exchange interaction between nearest-neighbor copper ions in edge-sharing chains J₁ depends sensitively on the Cu-O-Cu bond angles. In addition to J₁, the exchange interaction between next-nearest-neighbor copper ions J₂ has sufficient contribution to the magnetic properties. We calculate J₁ and J₂ for all the copper oxides containing edge-sharing Cu-O chains and discuss the magnetic properties.