Possible Kondo physics near a metal-insulator crossover in the a-site ordered perovskite CaCu3Ir4O12. 
The A-site ordered perovskite (AA(3)')B(4)O(12) can accommodate transition metals on both A' and B sites in the crystal structure.  Because of this structural feature, it is possible to have narrow-band electrons interacting with broadband electrons from different sublattices.  Here we report a new A-site ordered perovskite (CaCu(3))Ir(4)O(12) synthesized under high pressure.  The coupling between localized spins on Cu(2+) and itinerant electrons from the Ir-O sublattice makes Kondo-like physics take place at a temperature as high as 80 K. Results from the local density approximation calculation have confirmed the relevant band structure.  The magnetization anomaly found at 80 K can be well rationalized by the two-fluid model.