Phonons and excitonic complex in a monolayer semiconductor

Abstract

The coupling between spin, charge, and lattice degrees of freedom plays an important role in a wide range of fundamental phenomena. Monolayer semiconductor is an emerging platform for studying these coupling effects due to unique spin-valley locking physics for hosting rich excitonic species and reduced screening for strong Coulomb interaction. In this talk, I will present the observation of both symmetry-allowed and -forbidden valley phonons, i.e. phonons with momentum vectors pointing to the corners of Brillouin zone, in a monolayer semiconductor WSe2. We unravel a series of photoluminescence peaks as valley phonon replicas of neutral and charged dark excitons, as well as intrinsic donor bound excitonic states with anomalously long population lifetime (> 5 µs).Our work shows monolayer WSe2 is a prime candidate for studying interactions between spin, pseudospin, and zone-edge phonons.