Energy cascades in polaritonic systems with energetic disorder observed by ultrafast two-dimensional white-light spectroscopy

Abstract Exciton-polaritons are hybrid states formed when molecular excitons are strongly coupled to photons trapped in an optical cavity. These systems have many attractive properties, including large delocalization lengths, but questions regarding the role of energetic disorder remain unanswered. Here, we fabricate microcavities with two different layers of semiconducting carbon nanotubes as a way of controlling the energetic disorder and exploring its impact on energy transfer. Using ultrafast two-dimensional white-light spectroscopy, we observe a delayed growth of a cross peak between the upper- and lower-polariton states. Using Redfield theory, we assign the growth to cascading energy transfer down a manifold of new electronic states created by energetic disorder that is of comparable magnitude to the light-matter coupling. These results broaden our understanding of energy transfer dynamics in exciton-polariton systems beyond the Rabi contraction picture and enable control over how energy is transported in polaritonic systems.