Coherent injection and control of ballistic charge currents in single-walled carbon nanotubes and graphite
Bibliographic record
Abstract
We report results from a comprehensive set of experiments to study coherently controlled electrical current injection in single-walled carbon nanotubes (SWNTs) and graphite. Photocurrents were injected at room temperature through the quantum interference of single- and two-photon absorption pathways induced by 150-fs optical pulses with 660--980 and 1320--1960-nm central wavelengths, respectively, and with maximum intensities of 10 and 0.15 GW cm${}^{\ensuremath{-}2}$, respectively. Detection of the photocurrents was achieved via the emitted terahertz radiation. For bulk graphite samples and collinearly polarized 750- and 1500-nm pulses incident along the $c$ axis, injected current densities up to 12 kA cm${}^{\ensuremath{-}2}$ have been observed just under the surface, independent of crystal azimuthal orientation and comparable to those generated in InP or GaAs. Current densities are \ensuremath{\sim}5 times smaller for cross-polarized pulses. A vertically aligned forest of carbon nanotubes (tube diameters \ensuremath{\sim}2.5 \ifmmode\pm\else\textpm\fi{} 1.5 nm) illuminated with 700- and 1400-nm pulses collinearly polarized along the alignment direction yields a maximum current of 8 nA per tube (current density of 35 kA cm${}^{\ensuremath{-}2}$). Terahertz emission drops by only 3.5 times after 90\ifmmode^\circ\else\textdegree\fi{} sample rotation about the normal, which is explained in terms of an imperfect alignment distribution (angular spread \ensuremath{\sim}19.5\ifmmode^\circ\else\textdegree\fi{}) and sample birefringence. Unaligned arc discharge and HiPco SWNTs with diameters of 1.44 \ifmmode\pm\else\textpm\fi{} 0.15 and 0.96 \ifmmode\pm\else\textpm\fi{} 0.15 nm, respectively, were sorted into semiconducting and metallic tubes. Photocurrents injected with collinearly polarized 750- and 1500-nm pulses in such semiconducting SWNTs showed peak current magnitudes similar to those in the aligned nanotubes, while metallic tubes yielded currents at least ten times smaller. Semiconducting SWNT currents showed spectral features as the second-harmonic wavelength varied from 660 to 980 nm, which were more consistent with current injection based on band-band transitions than on excitonic absorption effects.
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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) | 0.000 | 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".