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Direct Identification of Valley Coherence and Its Manipulation in Monolayer Two-Dimensional Semiconductor.
Haonan Wang1, Keisuke Shinokita1, Kenji Watanabe2
1Institute of Advanced Energy, Kyoto University, Uji, Kyoto 611-0011, Japan.
ACS Nano
|June 4, 2025
Summary
Researchers directly measured intervalley coherence in WSe2, revealing coherence times of 200-300 fs. Carrier doping extended this valley coherence, paving the way for quantum-state manipulation.
Area of Science:
- Condensed Matter Physics
- Materials Science
- Quantum Information Science
Background:
- Monolayer 2D semiconductors exhibit valley degrees of freedom due to broken inversion symmetry and spin-orbit coupling.
- Valley pseudospin in K and K' valleys holds potential for quantum-state manipulation.
- Direct time-domain probing of valley coherence is challenging due to intervalley decoherence during light emission.
Purpose of the Study:
- To demonstrate direct measurement of intervalley coherence between K and K' valley excitons.
- To investigate the influence of carrier doping and external bias on valley coherence time.
- To elucidate the mechanisms governing valley decoherence in 2D materials.
Main Methods:
- Utilized polarized interferometry in a monolayer WSe2 device.
- Measured intervalley coherence time as a function of excitation power and temperature.
- Applied external bias voltage for electron and hole carrier doping.
Main Results:
- Achieved direct measurement of intervalley coherence with times ranging from 200-300 fs.
- Observed asymmetric modulation of coherence time and polarization under carrier doping.
- Extended valley coherence time up to 400 fs under high electron doping.
Conclusions:
- Established a viable method for direct time-domain probing of valley coherence.
- Elucidated the dependence of valley decoherence on carrier polarity and doping.
- Provided insights for advancing quantum-state manipulation using valley pseudospin.
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