Journal
NATURE PHYSICS
Volume 12, Issue 7, Pages 677-+Publisher
NATURE RESEARCH
DOI: 10.1038/NPHYS3674
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Funding
- US Derailment of Energy (DoE), Office of Science, Basic Energy-Science (BES) [DE-SC0012070]
- SHINES
- NSF [DMR-1306878]
- Welch Foundation [F-1662, F-1473]
- KAUST Saudi Arabia, Academia Sinica Taiwan
- AOARD USA [FA23861510001]
- Ministry of Science and Technology Taiwan [MOST 104-2218-E-035-010, 104-2628-E-035-002-MY3]
- Direct For Mathematical & Physical Scien
- Division Of Materials Research [1306878] Funding Source: National Science Foundation
- U.S. Department of Energy (DOE) [DE-SC0012070] Funding Source: U.S. Department of Energy (DOE)
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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(1-4). Interest in valleytronics has been revived in recent years following the discovery of atomically thin materials such as graphene and transition metal dichalcogenides(5-7). 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 WSe2 (refs 8,9). 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.
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