Fermi Surface and Band Dispersions of M_xCoO₂ (M: Na, K, and Rb) Studied by Angle-Resolved Photoemission Spectroscopy

Abstract

We have performed angle-resolved photoemission spectroscopy (ARPES) on M_xCoO₂ (M: Na, K, and Rb) with both soft X-ray and ultraviolet light to clarify the electronic structure intrinsic to the bulk CoO₂ plane. We observed a large holelike a_1g Fermi surface centered at the Γ(A) point with no signatures for a theoretically predicted small e^′_g hole pocket around the K(H) point, irrespective of the species of alkali metal and its content (x). We also found that the band dispersion near the Fermi level shows a kink structure indicative of the band hybridization and/or the strong mass renormalization due to electron-phonon coupling.