Ultrafast exciton dynamics in transition metal dichalcogenides: role of phonons and Coulomb interactions

Underlying relaxation processes following light excitation in semiconductors are key in materials-based quantum information science. These processes are broadly studied in transition metal dichalcogenides (TMDs), where constructed atomistic design allows for tunable excited-state properties, lifetime, and stability. In this talk, I will describe our new ab initio theoretical approach to compute exciton decomposition in these systems, paving a route to explore microscopic processes occurring between optical absorption and emission. Our approach, based on a Lindblad density matrix formalism, captures quantum many-body effects by combining predictive assessment of the exciton states and a band-resolved analysis of their scattering with phonons as well as Coulomb scattering. We explore the effect of mixed exciton states on both momentum and spin transitions, demonstrated on a commensurate MoSe₂-WSe₂ heterobilayer and study how these vary as a function of time and initial excitation conditions. Our findings supply an understanding of the underlying exciton relaxation mechanisms, offering new insights into the concept of excitons as stable quantum states in functional materials.