Band structure and Fermi surface of La0.6 Sr0.4 MnO3 thin films studied by in situ angle-resolved photoemission spectroscopy

We have performed an in situ angle-resolved photoemission spectroscopy (ARPES) on single-crystal surfaces of La0.6 Sr0.4 MnO3 (LSMO) thin films grown on SrTiO3 (001) substrates by laser molecular beam epitaxy, and investigated the electronic structure near the Fermi level (EF). The experimental results were compared with the band-structure calculation based on local density approximation + U. The band structure of LSMO thin films consists of several highly dispersive O 2p derived bands in the binding energy range of 2.0-6.0 eV and Mn 3d derived bands near EF. ARPES spectra around the Γ point show a dispersive band near EF indicative of an electron pocket centered at the Γ point, although the suppression of spectral weight occurs in the vicinity of EF. Compared with the band-structure calculation, the observed conduction band is assigned to the Mn 3d eg majority-spin band responsible for the half-metallic nature of LSMO. We have found that the estimated size of the Fermi surface is consistent with the prediction of the band-structure calculation, while the band width becomes significantly narrower than the calculation. Also, the intensity near EF is strongly reduced. The origin of these discrepancies between the experiment and the calculation is discussed based on the strong electron correlation and the strong electron-phonon coupling.