Nonlinear optical probing of electric field induced oxygen migrations in Fe doped SrTiO$_{3}$

We report on our recent study of the electric field induced oxygen migration dynamics and defect states near the interface in Fe-doped SrTiO$_{3}$ single crystals by optical second harmonic generation (SHG) using a femtosecond Ti:sapphire laser at 800 nm wavelength. By varying both the incidence and the output angles, we identified a strong correlation between the measured SHG signals and the microscopic defect textures of the samples. Significant changes in SHG intensities and phases are explained by the formation and extension of oxygen vacancies and crystalline distortions near Fe defect centers. Our results show that the SHG technique is a powerful tool for detecting local environment near interfaces and oxygen migrations in ferroelectric structures.