Variation of strong correlation effects in A-site ordered perovskites CaCu3Ti4-xRuxO12: Photoemission and inverse photoemission studies

TL;DR

This study investigates how strong correlation effects evolve in A-site ordered perovskites CaCu3Ti4-xRuxO12 using photoemission and inverse photoemission spectroscopy, revealing the role of Ti and Ru in electronic structure and metal-insulator transition.

Contribution

It provides systematic spectroscopic analysis of correlation effects across different Ru doping levels, highlighting the impact of Ti and Ru on electronic states and phase transition.

Findings

Cu 3d states remain stable for x=0,1,3.5 but split at x=4

Ru doping reduces localization of Cu 3d states

Metal-insulator transition occurs between x=1 and x=3.5

Abstract

We have systematically studied the strong correlation effects in A-site ordered perovskites CaCu3Ti4-xRuxO12 (x = 0, 1, 3.5, and 4) by using photoemission and inverse photoemission spectroscopies. In x = 0, 1, 3.5, the peak positions of the strongly correlated Cu 3d states around -3.8 eV and Ti 3d states around 3.6 eV little change. On the other hand, in x = 4, the Cu 3d states split into two peaks around -2.5 and -4 eV. These indicate that Ti plays an important role to retain the strong correlation effects. In addition, the multiplet structures of Cu 3d final states from -8 to -14 eV become weak as Ru increases, indicating the reduction of the localized characters of Cu 3d states. At the Fermi level, we observe the absence of spectral weight in x = 0, 1 and the development of Ru 4d in-gap states in x = 3.5, 4, which give rise to the metal-insulator transition between x = 1 and x = 3.5.