1s-intraexcitonic dynamics in monolayer MoS2 probed by ultrafast mid-infrared spectroscopy

• DOI: 10.1038/ncomms10768
• Publication Date: 2016-02-25T10:30:00Z
• Authors: Soonyoung Cha; Ji Ho Sung; Sangwan Sim; Jun Park; Hoseok Heo; Moon-Ho Jo; Hyunyong Choi
• Keywords: GIANT BANDGAP RENORMALIZATION; Science; Q; TERAHERTZ; TRANSITIONS; CARRIER DYNAMICS; 01 natural sciences; Article; ENERGY; STATES; EXCITATION; 0103 physical sciences; DISULFIDE; MONO LAYER; GENERATION

AbstractThe 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.