Energy dissipation via the lattice in nonlinear phononics: coupling pathways and scattering rates from first principles in LaAlO₃

The nonlinear phononics mechanism involves the coherent optical excitation of infrared-active phonons that, via anharmonic coupling, induce large quasistatic, unidirectional displacement of Raman-active phonons. This process occurs on sub-picosecond timescales. On longer timescales, the motion of the IR phonon is damped and the system reaches a higher temperature via several energy and momentum transferring processes: electron-electron, phonon-phonon, and defect scattering. What are the pathways by which an excited IR-active phonon transfers energy to the other lattice degrees of freedom? We use first-principles theory together with symmetry considerations to explore phonon-phonon scattering in LaAlO3, an experimentally important nonlinear phononics material. We explore ways to quantify the contribution of low frequency modes in energy transfer, and attempt to better understand the time scales at play for different pathways so as to gain insight into ultrafast optical control of the crystal lattice.