Fermi surface evolution and luttinger theorem in NaxCoO2:: A systematic photoemission study -: art. no. 146401

We report a systematic angle-resolved photoemission study on NaxCoO2 for a wide range of Na concentrations (0.3 <= x <= 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(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.