Coherent charge-phonon correlations and exciton dynamics in orthorhombic CH3NH3PbI3 measured by ultrafast multi-THz spectroscopy
Bibliographic record
Abstract
We use time-resolved multi-terahertz spectroscopy for the range 4–40 meV to probe coherent and incoherent ultrafast charge carrier and exciton dynamics in the low temperature orthorhombic phase of the hybrid metal halide perovskite CH3NH3PbI3. Time- and energy-resolved terahertz reflectivity maps reveal strongly damped but coherent oscillations in the 2–4 THz reststrahlen band, indicating charge coupling to a distribution of low energy phonon modes centered at 0.9 THz (3.7 meV or 30 cm−1). First-principles calculations reveal that these modes are entirely of mixed organic/inorganic sublattice character, with the power spectrum of the coherent oscillations showing a high frequency cutoff just at the onset of organic cation-only vibrations. Two anomalous reflectivity signatures are observed which are not phonon related, which we assign to a free exciton at 12 meV appearing on a 0.5 ps time scale and a defect bound exciton at 29–32 meV appearing on slower 1 ps time scale. Our measurements reveal the coherent coupling of charges to low energy vibrations of mixed sublattice character and the presence of two distinct populations of free and bound excitons at low temperatures.
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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".