Photoemission study of AgTO2 delafossites (T=Fe, Co, Ni)

The electronic structures of the AgTO2 delafossites (T = Fe, Co, Ni) have been investigated using photoemission spectroscopy. T 2p spectra exhibit satellite structures around 6 eV below main peaks, reflecting the strong on-site 3d Coulomb interaction. T 2p spectra of AgTO2 (T=Fe, Co, Ni) are similar to those of alpha-Fe2O3, CoO, and NiO, respectively, suggesting the strong covalent bonding in AgTO2. The valence-band spectrum of Ag0.75CoO2 shows negligible spectral weight near E-F, consistent with its semiconducting behavior. The extracted Ag 4d and Co 3d partial spectral weight (PSW) distributions of Ag0.75CoO2 reveal a Small overlap between these two states, while the O 2p PSW shows a significant overlap with the Co 3d PSW. Such trends in the PSWs are consistent with those in the calculated partial densities of states of AgCoO2.