Exciton dynamics in marginally twisted <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>WS</mml:mi> <mml:msub> <mml:mi mathvariant="normal">e</mml:mi> <mml:mn>2</mml:mn> </mml:msub> </mml:mrow> </mml:math> homobilayer: Role of interlayer coupling, phonons, and intervalley scattering
Bibliographic record
Abstract
In moir\'e materials, excitons serve as optical probes because of the sensitivity to both valley-dependent electronic structure and many-body excitonic interactions. For angle-tuned twisted bilayers, lattice reconstruction becomes significant at marginal twist angles, raising interesting questions about the optical characteristics of excitons both in the steady-state and nonequilibrium regimes. In this work, we investigate both the steady-state and the ultrafast transient exciton behaviors in a twisted ${\mathrm{WSe}}_{2}$ homobilayer (t-${\mathrm{WSe}}_{2}$) using reflection contrast, polarization-resolved photoluminescence, and ultrafast pump--probe spectroscopy. We report the emergence of two distinct intralayer excitons in the lattice reconstructed t-${\mathrm{WSe}}_{2}$, which are used to probe local electronic asymmetries and interlayer coupling in moir\'e domains. These excitons possess distinct temperature- and doping-dependent valley coherence and population dynamics, arising from the asymmetric interlayer coupling. Theoretical modeling via the Lindblad master equation highlights that the pure dephasing rate increases with hole doping, attributed to the enhanced electron-hole interactions. Ultrafast degenerate pump-probe spectroscopy reveals distinct fast decaying dynamics ($<1$ ps) for the two intralayer excitonic absorption species, ${X}_{1}$ and ${X}_{2}$, where the asymmetric interlayer coupling contributes more to the faster ${X}_{1}$ decay than ${X}_{2}$. Optical-pump and white-light probe spectroscopy further unveils a biexponential decay, where the fast component (${\ensuremath{\tau}}_{\mathrm{fast}}\phantom{\rule{4pt}{0ex}}\ensuremath{\approx}\phantom{\rule{4pt}{0ex}}0.7--0.9\phantom{\rule{0.28em}{0ex}}\mathrm{ps}$) signifies rapid radiative recombination with repopulation effects in the optical light cone. The slow component (${\ensuremath{\tau}}_{\mathrm{slow}}\phantom{\rule{4pt}{0ex}}\ensuremath{\approx}\phantom{\rule{4pt}{0ex}}100--300\phantom{\rule{0.28em}{0ex}}\mathrm{ps}$) is linked to exciton-phonon scattering and population relaxation via interlayer breathing phonons. We also present that intervalley scattering pathways, i.e., mediated by the $KQ$ transitions, are distinct from the monolayer counterpart. This work provides detailed insights into the exciton population dynamics in twisted homobilayers, highlighting the role of intervalley and exciton-phonon interactions in the transient multiple exciton complex behaviors.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".