  The electronic structure of Na2Ti2Sb2O, a parent compound of the newly
discovered titanium-based oxypnictide superconductors, is studied by photon
energy and polarization dependent angle-resolved photoemission spectroscopy
(ARPES). The obtained band structure and Fermi surface agree well with the band
structure calculation of Na2Ti2Sb2O in the non-magnetic state, which indicating
that there is no magnetic order in Na2Ti2Sb2O and the electronic correlation is
weak. Polarization dependent ARPES results suggest the multi-band and
multi-orbital nature of Na2Ti2Sb2O. Photon energy dependent ARPES results
suggest that the electronic structure of Na2Ti2Sb2O is rather two-dimensional.
Moreover, we find a density wave energy gap forms below the transition
temperature and reaches 65 meV at 7 K, indicating that Na2Ti2Sb2O is likely a
weakly correlated CDW material in the strong electron-phonon interaction
regime.
