| NaxCoO2 · yH2O is one of very few transition metal oxides, besides high TC cuprates, to be superconducting at low temperature. This dissertation presents a systematic study on the electronic structure on its parent compound NaxCoO2 , by angle-resolved photoemission spectroscopy (ARPES).; We first present the measurement of the shallow core levels, where a surface state component for Na 2p core level is found. Then we focus on a comprehensive investigation on the low energy excitations of NaxCoO2 (0.30 < x, 0.72). The Fermi surface topology study and its Na content (carrier concentration) dependence is presented in details. Unlike what is predict by LDA band calculation, only one large hole-like Fermi surface centered at the zone center (Gamma point) is observed. The predicted small Fermi surface pockets near the zone corners (K points) do not exit. Instead, we found that the top of the "pocket" band sinks below the Fermi energy, even when the Na concentration x is reduce to 0.3. By following the size of the large Fermi surface, we found that the Luttinger theorem of electron counting is satisfied within the experimental uncertainties. At the end, a complete determination of the t2g band complex in Na xCoO2 (x = 0.3, 0.48, and 0.72) is extracted from our ARPES data. |
