Ultrafast Dynamics of Quasiparticle Formation in Structurally Tunable Materials

The formation of localized electronic states reflects the fundamental physics of coupling between electronic and lattice dynamics, as first noted by Landau who in 1933 described the process of polaron formation as “the electron digs its own hole” and is trapped there. Localization of electronic states plays a critical role in determining the properties of a wide range of materials: polaron formation has a profound impact on charge transport properties of electronic materials, and formation of self-trapped excitons, or exciton-polarons, dramatically changes optical properties and energy transport mechanisms. I will present time-resolved studies of the dynamics of the localization process, focusing on the formation and evolution of self-trapped excitons and polarons. The experiments are carried out in quasi-one-dimensional materials in which the strength of the electron-phonon coupling that drives the dynamics can be systematically tuned by varying the material composition [1]. The studies use a combination of ultrafast time-resolved techniques that are sensitive to the electronic, vibrational, and structural dynamics that accompany self-trapping, including femtosecond optical spectroscopy in the vibrationally impulsive limit, time-resolved terahertz spectroscopy, and time-resolved x-ray spectroscopy.​