Electronic structure of hexagonal rare-earth manganites RMnO$_3$

The optical spectra of single crystals of hexagonal rare-earth manganites RMnO$_3$ (R=Sc, Y, Er) are studied in the range from 0.7 to 5.4 eV. It is found that the spectra substantially differ from the spectra of orthorhombic manganites in both the positions of spectral features and their polarization anisotropy. It is shown that the optical absorption edge is determined by an abnormally strong ($k\simeq 1$) and narrow electric dipole transition with the center at approximately 1.6 eV with light polarization in the basal plane of the crystal. This transition can be treated with confidence as charge transfer from oxygen to manganese. The experimental results are in many instances substantially different from the first-principles calculations of the electronic structure of YMnO$_3$ published recently and, hence, may serve as a reliable basis for the further improvement of computational methods.