Photoemission and x-ray absorption study of the two-dimensional triangular lattice superconductor Na0.35CoO2•1.3H2O -: art. no. 012508

We have investigated the electronic structure of a triangular lattice superconductor Na0.35CoO2.1.3H(2)O (T(c)similar to5 K) by photoemission and x-ray absorption spectroscopy. The Co 2p x-ray absorption and Co 2p-3d resonant photoemission clarified that the valence band near the Fermi level is mainly constructed by the narrow Co 3d t(2g) states at the binding energy of 1.0 eV with the low-spin configuration. In the resonant photoemission, Auger features coexist with the resonant enhancements, while the charge-transfer satellites are observed in the photoemission spectra of a Co 2p core levels. It is also expected that the narrow t(2g) band reflects on the importance of an electron-phonon coupling. Besides, O 1s and Co 1s x-ray absorption spectroscopy reveal that intercalated water condenses into a two-dimensional ice and showing no influence on a carrier doping.