We measured the optical properties of epitaxial thin films of the metastable hexagonal polymorph of LuFeO3 by absorption spectroscopy, magnetic circular dichroism, and photoconductivity. Comparison with complementary electronic structure calculations reveals a 1.1 eV direct gap involving hybridized excitations at the Γ and A points, with a higher energy direct gap at 2.0 eV. Both charge gaps nicely overlap the solar spectrum.
References
25 T in the Split-Florida Helix at the National High Magnetic Field Laboratory refers to the magnetic field strength within the sample volume at the magnet's mid-plane location. For MCD, which requires magneto-optical Faraday geometry, we have displaced the sample slightly above the mid-plane and thereby achieve field strengths as high as 30 T.
The calculated conduction bands are also more dispersive than those in the spinel ferrites.18,25
First, there is a feature in the DOS around −0.9 eV and from here it is ≈1.5 eV to the conduction band edge plus a rigid shift that is noted by the difference between theory and experiment (0.9 vs 1.1 eV band gap). Second, we see a feature in the DOS around −1.6 eV and from here it is ≈2.1 eV to the conduction band edge, which again via the rigid shift correlates to the smaller intensity feature in the MCD. Finally, we see a sharp rise in the DOS just after the −1.6 eV node. This results in a feature in the MCD that is not fully resolved but present none-the-less. If we take a qualitative look at the slopes for these three regions, we see that the first is a fairly strong slope which gives a strong intensity in the MCD response. The second is far less dispersed and thus has a significantly weaker contribution to the response. The final region has a steep slope and this is represented in the data as a significant increase in response.
