Band structure and Fermi surface of La0.6Sr0.4MnO3 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 La0.6Sr0.4MnO3 (LSMO) thin films grown on SrTiO3 (001) substrates by laser molecular beam epitaxy, and investigated the electronic structure near the Fermi level (E-F). 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 E-F. ARPES spectra around the Gamma point show a dispersive band near E-F indicative of an electron pocket centered at the Gamma point, although the suppression of spectral weight occurs in the vicinity of E-F. Compared with the band-structure calculation, the observed conduction band is assigned to the Mn 3de(g) 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 E-F 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.