Origin of the 2 eV peak in optical absorption spectra of LaMnO₃: An explanation based on the orbitally degenerate Hubbard model

We investigated the temperature-dependent optical absorption spectra of LaMnO₃ and NdMnO₃ epitaxial thin films. We found that both spectra have strong absorption features around 2 eV, and that the 2 eV peak of LaMnO₃ has a weak temperature dependence. As the La ions are replaced with Nd ions, the spectral weight of the peak becomes suppressed. From careful comparisons with the orbitally degenerate Hubbard model, we could explain most of the spectral features of the 2 eV peak observed in the absorption spectra. We also found a fine structure of three sub-peaks in the 2 eV peak, whose origin was considered based on currently available ideas.