Unraveling nonlinear formation and relaxation of excitons in atomically thin 2D semiconductors

Transition metal dichalcogenide semiconductors are layered van der Walls materials that exhibit exceptional optoelectronic properties in monolayer form. Their atomically thin nature and reduced long-range dielectric screening make them ideal systems in which to study many-body electronic states. Here, the dynamics of several higher-order exciton states in monolayer-WSe₂ are probed using temperature-, energy-, and power-dependent time-resolved optical spectroscopy. These studies reveal a complex interplay between multiexciton states and single-exciton states in 2D materials that depends on both the density and excitation energy of the initial exciton population. In addition, the presence of defect-bound excitons is found to drastically alter the formation of multiexciton states. This competition between exciton trapping and multiexciton formation highlights the need for high-quality materials to enhance multiexciton physics. Understanding these formation and relaxation dynamics of the rich manifold of exciton states is critical for leveraging this new class of 2D semiconductors for advanced technologies.