Light-induce ferroelectric transition in SrTiO₃ from quantum simulations

Strontium titanate (STO) has been extensively investigated due to the persistent second-harmonic generation (SHG) signal observed following irradiation with a strong THz pulse, which has been associated with a light-induced ferroelectric transition. Theoretical validation of this process is challenging, as it requires incorporating nuclear effects into nonequilibrium dynamics — a task that has so far been feasible only in models with limited degrees of freedom.

In this work, we employ the time-dependent self-consistent harmonic approximation (TD-SCHA) to simulate nuclear quantum dynamics in a realistic STO supercell. Crucially, we introduce a method for deriving an analytic expression for the quantum forces acting on the system. This approach not only enhances the accuracy of integrating the TD-SCHA differential equations but also provides deeper insights into the influence of quantum effects on the material’s dynamics.

Our fully first-principles simulations on STO confirm that irradiation of high-frequency infrared-active modes with a strong resonant pulse leads to the quenching of low-frequency phonons fluctuations [1], potentially driving a light-induced phase transition.

[1] M. Fechner et al., Nature Materials 23 (2024)