  Superionic conductors, or solid-state ion-conductors surpassing 0.01 S/cm in
conductivity, can enable more energy dense batteries, robust artificial ion
pumps, and optimized fuel cells. However, tailoring superionic conductors
require precise knowledge of ion migration mechanisms that are still not well
understood, due to limitations set by available spectroscopic tools. Most
spectroscopic techniques do not probe ion hopping at its inherent picosecond
timescale, nor the many-body correlations between the migrating ions, lattice
vibrational modes, and charge screening clouds--all of which are posited to
greatly enhance ionic conduction. Here, we develop an ultrafast technique that
measures the time-resolved change in impedance upon light excitation which
triggers selective ion-coupled correlations. We also develop a cost-effective,
non-time-resolved laser-driven impedance method that is more accessible for
lab-scale adoption. We use both techniques to compare the relative changes in
impedance of a solid-state Li+ conductor Li0.5La0.5TiO3 (LLTO) before and after
UV to THz frequency excitations to elucidate the corresponding
ion-many-body-interaction correlations. From our techniques, we determine that
electronic screening and phonon-mode interactions dominate the ion migration
pathway of LLTO. Although we only present one case study, our technique can
extend to O2-, H+, or other charge carrier transport phenomena where ultrafast
correlations control transport. Furthermore, the temporal relaxation of the
measured impedance can distinguish ion transport effects caused by many-body
correlations, optical heating, correlation, and memory behavior.
