Angle-resolved photoemission study of superconducting cobalt oxide Na$_{x}$CoO$_{2}$ yH$_{2}$O

Superconducting cobalt oxide Na$_{x}$CoO$_{2}$ yH$_{2}$O is studied by angle-resolved photoemission spectroscopy. We report the Fermi surface topology and electronic structure near the Fermi level in the normal state of Na$_{x}$CoO$_{2}$ yH$_{2}$O. Our result indicates the presence of the hexagonal Fermi surfce centered at $\Gamma $ point, while the small pocket Fermi surfaces along $\Gamma $-K direction are absent, similar to Na$_{x}$CoO$_{2}$. The top of the e$_{g}$' band, which is expected in band calculations to form the small pocket FSs, extends to within $\sim $30 meV below Fermi level, more closer to Fermi level than in Na$_{x}$CoO$_{2}$. Its possible role in superconductivity will be discussed, comparing with other experimental and theoretical results.