Theory of Exciton-Exciton Interactions in Monolayer Transition Metal Dichalcogenides

Two-dimensional layers of transition metal dichalcogenides (TMDCs) represent semiconductors with a complex single-particle bandstructure and reduce screening of the three-dimensional Coulomb interaction. The efficient Coulomb interaction causes optical excitations close to the band edge to be dominated by strongly correlated, bound electron-hole pairs, called excitons. Here, a theoretical formalism is presented to efficiently describe the optical dynamics of atomically thin TMDCs in a naturally adapted two particle exciton basis. As an example, Coulomb intravalley coupling, intervalley exchange, as well as intrinsic and Dexter-like intervalley interactions are discussed in Hartree-Fock approximation.