First-principles study of the linear electro-optical response in strained SrTiO3

We report a density functional theory study of the Pockels effect (linear electro-optical effect) in epitaxially strained SrTiO3. The electro-optical response is calculated for biaxial strain values ranging from -2.0 to 2.0% relative to the theoretically optimized lattice constant. Under 1.0% tensile strain, the Pockels tensor components increase dramatically, with the largest components reaching maximum values of r(111) = r(222) = 505.64 pm/V. Under 1.2% compressive strain, the Pockels tensor exhibits a similarly large peak with a maximum value of r(333) = 236.55 pm/V. These peaks in the electro-optical response originate from the softening of the phonon modes associated with ferroelectric phase transitions that result in the loss of inversion symmetry. Our results suggest that under the right circumstances SrTiO3 can yield a very large electro-optical response, comparable to that of BaTiO3, which has one of the largest known responses.