Seminar Hanan Dery

Rochester University

Hexcitons and oxcitons in monolayer WSe2

Hydrogen-like bound states of photoexcited electron-hole pairs in semiconductors — that is, excitons — have been a focus of considerable study for more than half a century. In undoped direct-gap semiconductors, neutral excitons comprise the photogenerated electron and hole in the conduction and valence bands (CB and VB), respectively, and typically manifest as discrete optical resonances below the free-particle band-gap energy. More interesting states arise when electron-hole (e-h) pairs are photoexcited into doped semiconductors containing a Fermi-sea of mobile carriers.In the archetypal monolayer semiconductor WSe2, the distinct ordering of spin-polarized valleys (low-energy pockets) in the CB allows for studies of not only simple neutral excitons and chargedexcitons (i.e., trions), but also more complex many-body states that are predicted at higher electron densities [1]. I will discuss magneto-optical measurements of electron-rich WSe2 monolayers [2], and interpret the spectral lines that emerge at high electron doping as optical transitions of 6-body exciton states (“hexcitons”) and 8-body exciton states (“oxcitons”). These many-body states emerge when a photoexcited electron-hole pair interacts simultaneously with multiple Fermi seas, each having distinguishable spin and valley quantum numbers