Strong correlation effects in the A-site ordered perovskite CaCu3Ti4O12 revealed by angle-resolved photoemission spectroscopy.

We report angle-resolved photoemission spectroscopy results of A-site ordered perovskite CaCu3Ti4O12. We have observed the clear band dispersions, which are shifted to the higher energy by 1.7 eV and show the band narrowing around 2 eV in comparison with the local density approximation calculations. In addition, the high-energy multiplet structures of Cu 3d8 final states have been found around 8-13 eV. These results reveal that CaCu3Ti4O12 is a Mott-type insulator caused by the strong correlation effects of the Cu 3d electrons well hybridized with O 2p states. Unexpectedly, there exists a very small spectral weight at the Fermi level in the insulator phase, indicating the existence of isolated metallic states. [ABSTRACT FROM AUTHOR]