Electronic structure of MnO studied by angle-resolved and resonant photoemission.

Abstract

Results are reported from angle-integrated, angle-resolved, and resonant photoemission measurements on cleaved MnO single crystals using synchrotron radiation. Normal-emission spectra from a cleaved (100) surface indicate that the relative dispersion of Mn 3d states in the valence band is less than \ifmmode\pm\else\textpm\fi{}0.1 eV along \ensuremath{\Gamma}--\ensuremath{\Delta}--X in the Brillouin zone, which supports the view of highly localized 3d electrons on the ${\mathrm{Mn}}^{2+}$ cations. The results of polarization-dependent and off-normal-emission measurements are also consistent with a localized Mn 3d orbital picture. To explain the presence of satellite photoemission peaks, a hybridization between Mn 3d and O 2p valence states must be invoked. The degree of hybridization is evident from resonant-photoemission measurements at the Mn 3p\ensuremath{\rightarrow}3d absorption threshold. The antiresonant behavior of the 3d-derived states near the top of the valence band in constant-initial-state spectra suggests that MnO is a charge transfer rather than a Mott insulator. The experimental results are discussed in the context of recent cluster and band theories which have been proposed to explain the insulating nature and electronic structure of MnO.