Strong Correlation Effects of A-site Ordered Perovskite CaCu3Ti4O12 revealed by Angle-Resolved Photoemission Spectroscopy

TL;DR

This study uses ARPES to reveal strong electron correlation effects in CaCu3Ti4O12, showing it as a Mott insulator with unexpected metallic states at the Fermi level.

Contribution

First ARPES investigation of CaCu3Ti4O12 demonstrating strong correlation effects and revealing its Mott-insulating nature with anomalous metallic states.

Findings

CaCu3Ti4O12 is a Mott insulator caused by strong Cu 3d electron correlations.

ARPES shows band shifts and narrowing compared to calculations.

Presence of small spectral weight at the Fermi level indicating metallic states.

Abstract

We report angle-resolved photoemission spectroscopy (ARPES) results of A-site ordered perovskite CaCu$_3$Ti$_4$O$_{12}$. 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 3$d^8$ final-states have been found around 8 - 13 eV. These results reveal that CaCu$_3$Ti$_4$O$_{12}$ is a Mott-type insulator caused by the strong correlation effects of the Cu 3$d$ electrons well hybridized with O 2$p$ states. Unexpectedly, there exist a very small spectral weight at the Fermi level in the insulator phase, indicating the existence of isolated metallic states.