Realistic exciton-phonon coupling is too weak for Dyakonov-Perel motional narrowing in MoS2; full-Brillouin-zone intervalley scattering shortens valley depolarization 3–4× to ~50 fs (300 K) and ~130 fs (10 K).
Phonon-mediated exciton relaxation in two-dimensional semiconductors: selection rules and relaxation pathways
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abstract
Exciton-phonon coupling (ExPC) is crucial for energy relaxation in semiconductors, yet the first-principles calculation of such coupling remains challenging, especially for low-dimensional systems. Here, an accurate algorithm for calculating ExPC is developed and applied in exciton relaxation problems in monolayer WSe2. Considering the interplay between the exciton wave functions and electron-phonon coupling (EPC) matrix elements, we find that ExPC shows distinct selection rules from the ones of EPC. By employing the Wannier exciton model, we generalize these selection rules, which state that the angular quantum numbers of the exciton must match the winding numbers of the EPC matrix elements for the ExPC to be allowed. To verify our theory and algorithm, we calculate inter-valley exciton relaxation pathways, which agrees well with a recent experiment.
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cond-mat.mtrl-sci 1years
2026 1verdicts
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Exciton valley depolarization in monolayer MoS2: non-Markovian quantum dynamics, intervalley scattering, and the breakdown of the Dyakonov-Perel mechanism
Realistic exciton-phonon coupling is too weak for Dyakonov-Perel motional narrowing in MoS2; full-Brillouin-zone intervalley scattering shortens valley depolarization 3–4× to ~50 fs (300 K) and ~130 fs (10 K).