Exploring light-induced ferroelectricity in SrTiO3: phonon-phonon coupling as a function of epitaxial strain*

Recent experiments have shown a transient ferroelectric phase is accessible through optical excitation of infrared active (IR) phonons in bulk, paraelectric SrTiO₃ [Science Vol 364, Issue 6445 pp. 1075-1079 and 1079-1082 (2016)]. One explanation for this behavior is that when the lowest frequency IR phonon is excited, a transient lattice strain induced by the displaced IR phonon stabilizes the ferroelectric phase [arXiv:2106.03957]. We further explore a complementary pathway of phonon-phonon coupling for stabilization of the ferroelectric phase using theory and first-principles calculations (see also [PRB 95, 134113 (2017)]). Our preliminary results suggest that epitaxial strain provides a handle for tuning the optically induced ferroelectric phase transition in SrTiO₃.