title: Coherent and Incoherent Coupling Dynamics between Neutral and Charged Excitons in Monolayer MoSe2.
abstract: The optical properties of semiconducting transition metal dichalcogenides are dominated by both neutral excitons (electron-hole pairs) and charged excitons (trions) that are stable even at room temperature. While trions directly influence charge transport properties in optoelectronic devices, excitons may be relevant through exciton-trion coupling and conversion phenomena. In this work, we reveal the coherent and incoherent nature of exciton-trion coupling and the relevant time scales in monolayer MoSe2 using optical two-dimensional coherent spectroscopy. Coherent interaction between excitons and trions is definitively identified as quantum beating of cross peaks in the spectra that persists for a few hundred femtoseconds. For longer times up to 10 ps, surprisingly, the relative intensity of the cross peaks increases, which is attributed to incoherent energy transfer likely due to phonon-assisted up-conversion and down-conversion processes that are efficient even at cryogenic temperature.
authors.affiliation: Department of Physics and Center for Complex Quantum Systems, University of Texas at Austin , Austin, Texas 78712, United States.
authors.forename: Kai
authors.initials: K
authors.lastname: Hao
authors.affiliation: Department of Physics and Center for Complex Quantum Systems, University of Texas at Austin , Austin, Texas 78712, United States.
authors.forename: Lixiang
authors.initials: L
authors.lastname: Xu
authors.affiliation: Department of Physics, University of Regensburg , Regensburg 93040, Germany.
authors.forename: Philipp
authors.initials: P
authors.lastname: Nagler
authors.affiliation: Department of Physics and Center for Complex Quantum Systems, University of Texas at Austin , Austin, Texas 78712, United States.
authors.forename: Akshay
authors.initials: A
authors.lastname: Singh
authors.affiliation: Department of Physics and Center for Complex Quantum Systems, University of Texas at Austin , Austin, Texas 78712, United States.
authors.forename: Kha
authors.initials: K
authors.lastname: Tran
authors.affiliation: Department of Physics and Center for Complex Quantum Systems, University of Texas at Austin , Austin, Texas 78712, United States.
authors.forename: Chandriker Kavir
authors.initials: CK
authors.lastname: Dass
authors.affiliation: Department of Physics, University of Regensburg , Regensburg 93040, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Schüller
authors.affiliation: Department of Physics, University of Regensburg , Regensburg 93040, Germany.
authors.forename: Tobias
authors.initials: T
authors.lastname: Korn
authors.affiliation: Department of Physics and Center for Complex Quantum Systems, University of Texas at Austin , Austin, Texas 78712, United States.
authors.forename: Xiaoqin
authors.initials: X
authors.lastname: Li
authors.affiliation: National Institute of Standards & Technology , Boulder, Colorado 80305, United States.
authors.forename: Galan
authors.initials: G
authors.lastname: Moody
keywords: Quantum beats; coherent coupling; exciton; trion; two-dimensional materials