Fundamental Absorption Edge of SrTiO3

Detailed measurements of the fundamental absorption edge of SrTi${\mathrm{O}}_3$ between 6 and 300 K are reported. Because these results provide the first detailed data below 82 K, several new properties of this material have been observed. The energies of the fundamental transitions are found to have unusually small temperature dependence. It is also observed that the strengths of the phonon-emission and impurity-induced absorption processes are more strongly temperature dependent than is found in other materials. In addition, we propose a different explanation for the prominent shoulder in the absorption at 3.40 eV: that it is merely the saturation of the phonon-assisted transitions.