Observation of flat bands due to band hybridization in the 3d -electron heavy-fermion compound CaC u3 R u4 O12

Abstract

We report angle-resolved photoemission spectroscopy and first-principles numerical calculations for the band-structure evolution of the 3d heavy-fermion compound CaCu3Ru4O12. Below T∼200 K, we observed an emergent hybridization gap between the Cu 3d-electron-like band and the Ru 4d-hole-like band and the resulting flat band features near the Fermi level centered around the Brillouin-zone corner. Our results confirm the non-Kondo nature of the CaCu3Ru4O12, in which the Cu3dxy electrons are less correlated and not in the Kondo limit. Comparison between theory and experiment also suggests that other mechanisms may be needed to give a full quantitative explanation of the peculiar properties in this material.