Proceedings of September Meeting 2016 (NFM16)
Publication date: 14th June 2016
Solid knowledge of the electronic band structure of materials is a cornerstone of modern technology. In functional dielectrics and multiferroics, traditionally seen and used as insulating materials, electronic structures have been much less explored than in semiconductors. However, today, they gain in importance due to the growing interest for interactions of ferroic materials with light, namely in the context of unique photovoltaic or photoelectric properties.
In this study, we demonstrate how resonance Raman spectroscopy enables to probe electronic levels of the model multiferroic BiFeO3 (BFO). Using twelve different excitation wavelengths ranging from the blue (442 nm = 2.8 eV) to the near infrared (785 nm = 1.6 eV), we show that both the first- and second-order Raman signatures of the crystals show resonance phenomena that can be assigned to the direct and indirect band-gaps, and oxygen electronic defect levels. Temperature-dependent measurements provide the first experimental indication that the reported strong variation of the optical band-gap in BFO originates from a shrinking of the indirect electronic gap. More generally, our study suggests that Raman scattering at various wavelengths offers a powerful tool for the investigation of electronic excitations in multiferroic functional oxides (1).
(1) M. C. Weber, M. Guennou, C. Toulouse, M. Cazayous, Y. Gillet, X. Gonze and J. Kreisel, Physical Review B 93 125204 (2016).
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