Correlated Terahertz phonon-ion interactions control ion conduction in a solid electrolyte (2305.01632v3)

Abstract: Ionic conduction in solids that exceeds 1 mS/cm is predicted to involve collective phonon-ion interactions in the crystal lattice. Here, we use theory and experiment to measure the possible contribution of collective phonon-ion modes to Li+ migration in Li0.5La0.5TiO3 (LLTO). The ab initio calculations predict that the targeted excitation of individual TiO6 rocking modes can lead to a three order of magnitude increase in the Li+ jump rate as compared to the excitation of single vibrational modes in the lattice associated with heating. Experimentally, coherently driving the TiO6 rocking via terahertz (THz) illumination leads to a ten-fold decrease in the normalized impedance compared to the excitation of acoustic and optical phonons that are associated with heating. These findings provide new insights into phonon-coupled ion migration mechanisms and material design rules for ion conductors and opto-ionic materials.