title: 1s-intraexcitonic dynamics in monolayer MoS2 probed by ultrafast mid-infrared spectroscopy.
abstract: The 1s exciton--the ground state of a bound electron-hole pair--is central to understanding the photoresponse of monolayer transition metal dichalcogenides. Above the 1s exciton, recent visible and near-infrared investigations have revealed that the excited excitons are much richer, exhibiting a series of Rydberg-like states. A natural question is then how the internal excitonic transitions are interrelated on photoexcitation. Accessing these intraexcitonic transitions, however, demands a fundamentally different experimental tool capable of probing optical transitions from 1s 'bright' to np 'dark' states. Here we employ ultrafast mid-infrared spectroscopy to explore the 1s intraexcitonic transitions in monolayer MoS2. We observed twofold 1s→3p intraexcitonic transitions within the A and B excitons and 1s→2p transition between the A and B excitons. Our results revealed that it takes about 0.7 ps for the 1s A exciton to reach quasi-equilibrium; a characteristic time that is associated with a rapid population transfer from the 1s B exciton, providing rich characteristics of many-body exciton dynamics in two-dimensional materials.
authors.affiliation: School of Electrical and Electronic Engineering, Yonsei University, Seoul 120-749, Korea.
authors.forename: Soonyoung
authors.initials: S
authors.lastname: Cha
authors.affiliation: Center for Artificial Low Dimensional Electronic Systems, Institute for Basic Science (IBS), Pohang University of Science and Technology (POSTECH), Pohang 790-784, Korea.|Division of Advanced Materials Science, Pohang University of Science and Technology (POSTECH), Pohang 790-784, Korea.
authors.forename: Ji Ho
authors.initials: JH
authors.lastname: Sung
authors.affiliation: School of Electrical and Electronic Engineering, Yonsei University, Seoul 120-749, Korea.
authors.forename: Sangwan
authors.initials: S
authors.lastname: Sim
authors.affiliation: School of Electrical and Electronic Engineering, Yonsei University, Seoul 120-749, Korea.
authors.forename: Jun
authors.initials: J
authors.lastname: Park
authors.affiliation: Center for Artificial Low Dimensional Electronic Systems, Institute for Basic Science (IBS), Pohang University of Science and Technology (POSTECH), Pohang 790-784, Korea.|Division of Advanced Materials Science, Pohang University of Science and Technology (POSTECH), Pohang 790-784, Korea.
authors.forename: Hoseok
authors.initials: H
authors.lastname: Heo
authors.affiliation: Center for Artificial Low Dimensional Electronic Systems, Institute for Basic Science (IBS), Pohang University of Science and Technology (POSTECH), Pohang 790-784, Korea.|Division of Advanced Materials Science, Pohang University of Science and Technology (POSTECH), Pohang 790-784, Korea.
authors.forename: Moon-Ho
authors.initials: MH
authors.lastname: Jo
authors.affiliation: School of Electrical and Electronic Engineering, Yonsei University, Seoul 120-749, Korea.
authors.forename: Hyunyong
authors.initials: H
authors.lastname: Choi