Direct measurement of exciton valley coherence in monolayer WSe2

Kai Hao, Galan Moody, Fengcheng Wu, Chandriker Kavir Dass, Lixiang Xu, Chang Hsiao Chen, Liuyang Sun, Ming-yang Li, Lain-Jong Li, Allan H. MacDonald, Xiaoqin Li

Research output: Contribution to journalArticlepeer-review

231 Scopus citations

Abstract

In crystals, energy band extrema in momentum space can be identified by a valley index. The internal quantum degree of freedom associated with valley pseudospin indices can act as a useful information carrier, analogous to electronic charge or spin. Interest in valleytronics has been revived in recent years following the discovery of atomically thin materials such as graphene and transition metal dichalcogenides. However, the valley coherence time - a crucial quantity for valley pseudospin manipulation - is difficult to directly probe. In this work, we use two-dimensional coherent spectroscopy to resonantly generate and detect valley coherence of excitons (Coulomb-bound electron-hole pairs) in monolayer $WSe_{2}(refs,)$. The imposed valley coherence persists for approximately one hundred femtoseconds. We propose that the electron-hole exchange interaction provides an important decoherence mechanism in addition to exciton population recombination. This work provides critical insight into the requirements and strategies for optical manipulation of the valley pseudospin for future valleytronics applications.
Original languageEnglish (US)
Pages (from-to)677-682
Number of pages6
JournalNature Physics
Volume12
Issue number7
DOIs
StatePublished - Feb 29 2016

Bibliographical note

KAUST Repository Item: Exported on 2020-10-01
Acknowledgements: The theoretical and experimental collaboration is made possible by SHINES, an Energy Frontier Research Center funded by the US Derailment of Energy (DoE), Office of Science, Basic Energy-Science (BES) under award # DE-SC0012070. K.H., F.W., L.X., X.L. and A.H.M. have all received support from SHINES. Optical spectroscopy studies performed by K.H., C.K.D., L.S. and X.L. have been partially supported by NSF DMR-1306878 and Welch Foundation F-1662. A.H.M. also acknowledges support from Welch Foundation F-1473. L.J.L. is grateful for support from KAUST Saudi Arabia, Academia Sinica Taiwan, and AOARD FA23861510001 USA. C.-H.C. is grateful for support from the Ministry of Science and Technology Taiwan (MOST 104-2218-E-035-010 and 104-2628-E-035-002-MY3).

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