We have performed angle-resolved photoemission spectroscopy (ARPES) on MxCoO2 (M: Na, K, and Rb) to clarify electronic structure essential to the bulk CoO2 plane. By the bulk-sensitive ARPES measurement of Na0.72CoO2 using soft X-ray (hν = 600 eV) as a excitation source, we found a large holelike a1g Fermi surface centered at Γ(A) point but not around K(H) point, quite similar to the previous ARPES results using ultraviolet light. By elucidating the alkali-metal dependence of Fermi surface, we also found that appearance of large a1g Fermi surface and the absence of eg′ pocket is a common feature of MxCoO2, irrespective of the alkali metal.
- Cobalt oxide
- Electronic structure