Hexagonal films have been studied using x-ray absorption and optical spectroscopy. The crystal splitting of is extracted as and , and a 2.0 eV optical bandgap is determined assuming a direct gap. First-principles calculations confirm the experiments that the relative energies of crystal field splitting states do follow with slightly underestimated values and a bandgap of 1.35 eV.
REFERENCES
The lattice constants of films on YSZ and on pt buffered are the same within the experimental uncertainty, due to the fast structural relaxation (see Ref. 3). Our measurements show similar XAS spectra for the two kinds of films, while those of have worse statistics due to the charging problem.
These multiplets are divided into groups due to the p-d interactions, which have an energy scale of 5 eV (Ref. 21).
Our first principle calculations show a fairly flat top for the valence band, indicating a mixture of direct and indirect nature of the bandgap. Here, we made the assumption that the part of optical absorption spectrum shown in Fig. 3 inset is related to a direct bandgap according to the strong absorption coefficient () above the gap. The tail below the gap in Fig. 3 is consistent with a typical experimental artifact on film samples due to the reflections.
A 500 eV planewave cutoff and 6 × 6 × 3 k points mesh are used.
The energy threshold separating the localized and nonlocalized electronic states is chosen to be −7Ry. The muffin-tin radii are 2.35 Bohr for Lu, 1.98 Bohr for Fe, and 1.65 Bohr for O. The criterion for the number of plane waves is chosen to be , and the number of k points is 8 × 8 × 2 for A-type antiferromagnetic calculation.
