Fermi surface evolution and luttinger theorem in NaxCoO2: A systematic photoemission study

We report a systematic angle-resolved photoemission study on Na{sub x}CoO{sub 2} for a wide range of Na concentrations (0.3 {le} x {le} 0.72). In all the metallic samples at different x, we observed (i) only a single holelike Fermi surface centered around {Gamma} and (ii) its area changes with x according to the Luttinger theorem. We also observed a surface state that exhibits a larger Fermi surface area. The e{prime}{sub g} band and the associated small Fermi surface pockets near the K points predicted by band calculations are found to sink below the Fermi energy in a manner almost independent of the doping and temperature.