The latest discovery of high temperature superconductivity near 80K in
La3Ni2O7 under high pressure has attracted much attention. Many proposals are
put forth to understand the origin of superconductivity. The determination of
electronic structures is a prerequisite to establish theories to understand
superconductivity in nickelates but is still lacking. Here we report our direct
measurement of the electronic structures of La3Ni2O7 by high-resolution
angle-resolved photoemmission spectroscopy. The Fermi surface and band
structures of La3Ni2O7 are observed and compared with the band structure
calculations. A flat band is formed from the Ni-3dz2 orbitals around the zone
corner which is 50meV below the Fermi level. Strong electron correlations are
revealed which are orbital- and momentum-dependent. Our observations will
provide key information to understand the origin of high temperature
superconductivity in La3Ni2O7.Comment: 18 pages, 4 figure