Angle-resolved photoemission spectroscopy (ARPES) of Na0.7CoO2

Detailed study of the electronic structure of the layered Na0.7CoO2, doped Mott insulator with triangular Co lattice is performed by angle-resolved photoemission spectroscopy (ARPES). At low temperature Fermi surface is a centered hole pocket of hexagonal character shape in agreement with LDA. A broad valence band satellite at higher energies showing resonant enhancement at the 2p, 3p -> 3d excitations indicates large on-site Hubbard-U similar to 5 eV. A momentum dependent quasiparticle band near Fermi level that is flat and vanished at energies already above 70 meV or 80 meV gives a value of the single particle hopping t < 10 meV. This band is defined only in the region of non - Fermi liquid transport with linear growth of resistivity up to 120 K.