Nonlinear Phononics in Perovskite with Point Defects

Ultrafast light control of material properties is a novel route to dynamically control materials out-of-equilibrium. It is widely explored experimentally and several nonlinear phononic theories have been formulated. Generally, a pump light pulse will excite certain infrared (IR) active phonons; however, the phonons will dissipate the excitation and dephase owing to anharmonicity and coupling between other IR and Raman-active phonons. Here, we formulate and parameterize a physical model to study the evolution of these phonons and their excitations on point defects present in many perovskite oxides. We obtain phonon mode coupling parameters by fitting energy surfaces spanned by phonons calculated at the density functional theory (DFT) level. We then numerically solve the equations of motion to obtain the phonon dynamics, which we then correlate with defect dynamics by calculating changes in transition state energies to examine the effect of light-driven nonlinear phononics on defect kinetics.