Optical Properties of SrTiO3under Applied Stress and Electric Field

Motivated by recent experiments on the effects of uniaxial stress on the superconducting transition and normal-state transport properties of SrTi${\mathrm{O}}_3$, we have carried out a symmetry analysis, obtaining the perturbed band structure and optical selection rules for the cases of uniaxial stress along the [111] and [001] axes and of static electric field along [001]. A comparison of the last case with BaTi${\mathrm{O}}_3$ in the $C_{4v}$ ferroelectric phase suggests a model with a reversal in the order of the valence bands in SrTi${\mathrm{O}}_3$ relative to that proposed earlier. Selection rules for polarized light are obtained for both models and criteria for deciding experimentally which is correct are stated. An example is given of how the sign of the relative energy shift of the conduction valleys with stress may be determined optically.