Correlated Terahertz phonon-ion interactions dominate ion conduction in solid electrolyte Li0.5La0.5TiO3

Ionic conduction in solids that exceeds 0.01 S/cm is predicted to involve collective phonon-ion interactions in the crystal lattice. Here, we use theory and experiment to measure the contribution of possible collective phonon-ion modes to Li+ migration in Li0.5La0.5TiO3. The ab initio calculations reveal that only a few phonon modes, mostly TiO6 rocking modes below 6 Terahertz, provide over 40% of the energy required for the Li+ hop in Li0.5La0.5TiO3. Laser-driving the TiO6 rocking modes decreases the measured impedance ten-fold compared to exciting acoustic and optical phonons at similar energy densities. The decreased impedance persists on thermalization timescales. These findings provide new insights on phonon-coupled ion migration mechanisms, material design rules, and the potential for metastable states for opto-ionic materials.