Chen, Hao-YuHao-YuChenHsu, Hung-ChangHung-ChangHsuHuang, Chuan-ChunChuan-ChunHuangLi, Ming-YangMing-YangLiLi, Lain-JongLain-JongLiYA-PING CHIU2023-07-182023-07-182022-06-2819360851https://scholars.lib.ntu.edu.tw/handle/123456789/633929Resolving the momentum degree of freedom of photoexcited charge carriers and exploring the excited-state physics in the hexagonal Brillouin zone of atomically thin semiconductors have recently attracted great interest for optoelectronic technologies. We demonstrate a combination of light-modulated scanning tunneling microscopy and the quasiparticle interference (QPI) technique to offer a directly accessible approach to reveal and quantify the unexplored momentum-forbidden electronic quantum states in transition metal dichalcogenide (TMD) monolayers. Our QPI results affirm the large spin-splitting energy at the spin-valley-coupled Q valleys in the conduction band (CB) of a tungsten disulfide monolayer. Furthermore, we also quantify the photoexcited carrier density-dependent band renormalization at the Q valleys. Our findings directly highlight the importance of the excited-state distribution at the Q valley in the band renormalization in TMDs and support the critical role of the CB Q valley in engineering the quantum electronic valley degree of freedom in TMD devices.enatomically thin semiconductors; band renormalization; momentum degree of freedom; quasiparticle interference technique; scanning tunneling microscopy; transition metal dichalcogenidesjournal article10.1021/acsnano.2c02981355845482-s2.0-85131511670https://api.elsevier.com/content/abstract/scopus_id/85131511670