Electron-soft phonon scattering in n-type SrTiO3

SrTiO3 undergoes a cubic to tetragonal phase transition at T-c = 105-110 K, which can be described by a Brillouin zone corner Gamma(25) (111) soft phonon. Even though clear anomalies in specific heat, thermal expansion coefficient, and sound velocity have been observed, the correlation between phase transition and electronic transport properties in n-type doped SrTiO3 is still controversial. Here, we report phase transition induced electronic transport anomaly in temperature dependence of the temperature coefficient of resistance (TCR) consistently observed in a wide variety of SrTiO3-based systems by detailed transport measurements and first-principles calculations. The observed TCR anomaly, which can be well fitted with the electron-Gamma(25) soft phonon scattering around Tc, is found to be caused by anomalies in both mobility and carrier density, with the former taking the dominant role. Moreover, the magnitude of the anomaly is found to decrease with increasing carrier density. These findings demonstrate the role of the electron-Gamma(25) soft phonon scattering in the conduction mechanism in SrTiO3-based systems.