Temperature evolution of the band gap inBiFeO3traced by resonant Raman scattering

Abstract

Knowledge of the electronic band structure of multiferroic oxides, crucial for the understanding and tuning of photoinduced effects, remains very limited even in the model and thoroughly studied ${\mathrm{BiFeO}}_{3}$. Here, we investigate the electronic band structure of ${\mathrm{BiFeO}}_{3}$ using Raman scattering with twelve different excitation wavelengths ranging from the blue to the near infrared. We show that resonant Raman signatures can be assigned to direct and indirect electronic transitions, as well as in-gap electronic levels, most likely associated with oxygen vacancies. Their temperature evolution establishes that the remarkable and intriguing variation of the optical band gap can be related to the shrinking of an indirect electronic band gap, while the energies for direct electronic transitions remains nearly temperature independent.