Resonant photoemission spectroscopy of layered triangular lattices Ag ₂MO₂ (M = Ni and Mn): Evidence for M 3d states at Fermi level

We report on the soft X-ray photoemission and absorption spectroscopy of Ag₂NiO₂ and Ag₂MnO₂, which consist of alternate stacks of (Ag₂)⁺ and (MO₂) ^- layers. The core-level photoemission and absorption spectra indicate mainly trivalent Ni³⁺ in Ag₂NiO₂, and trivalent Mn³⁺ with an admixture of Mn²⁺ states in Ag ₂MnO₂. The M 2p-3d resonant photoemission clearly shows that the density of states at the Fermi level includes the M 3d character in both compounds. The results indicate that the Ni 3d and Mn 3d states at the Fermi level are responsible for the significant mass enhancement of carriers, as seen in the transport properties of Ag₂NiO₂ and Ag ₂MnO₂.