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Probing many-body interactions through excitons in monolayer transition-metal dichalcogenides

Advances in spintronics over the past decade are largely driven by manifestations of the spin-orbit coupling in crystals with reduced symmetries. In this talk, I will focus on exciton optical transitions in monolayer transition-metal dichalcogenides. The spin-split energy bands in these materials offer unique opportunities to study rich manybody physics. After reviewing recent experimental results of the photoluminescence and absorption in gated monolayer WSe2 and MoSe2, I will explain the behavior of neutral excitons in the presence of gate-induced charge density. I will then focus on peculiar spectral peaks that emerge at elevated charge density. These features have no counterparts in typical semiconductor quantum wells. To elucidate their nature, I will discuss the role of the intervalley Coulomb interaction and its resulting plasma excitations. The inclusion of this interaction seems to provide a self-consistent explanation for the optical properties in these materials when subjected to strong photoexcitation or elevated electron densities.