Single-quasiparticle stability and quasiparticle-pair decay in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">YBa</mml:mi></mml:mrow><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mrow><mml:mi mathvariant="normal">Cu</mml:mi></mml:mrow><mml:mn>3</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mrow><mml:mn>6.5</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>
Bibliographic record
Abstract
We report results and analysis of time-resolved photoinduced reflectivity experiments on the cuprate superconductor ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{6.5}$. The sample, which has ${T}_{c}=45\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, was characterized by a high degree of purity and Ortho II ordering. The change in reflectivity $\ensuremath{\Delta}R$ was induced and probed using pulses of $100$ femtosecond duration and photon energy $1.55\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ from a $\mathrm{Ti}$:Sapphire laser. We provide a detailed picture of the decay rate $\ensuremath{\gamma}$ of $\ensuremath{\Delta}R$ as a function of temperature $T$ and pump intensity $I$. At low $T$, $\ensuremath{\gamma}$ decreases linearly with decreasing $I$, extrapolating to nearly zero in the limit that $I$ tends to zero. At higher temperature $\ensuremath{\gamma}$ has the same linear dependence, but with nonzero limit as $I\ensuremath{\rightarrow}0$. In the interpretation of these results we assume that $\ensuremath{\Delta}R$ is proportional to the nonequilibrium quasiparticle density created by the laser. From an analysis of the $\ensuremath{\gamma}$ vs $I$ we estimate $\ensuremath{\beta}$, the coefficient of proportionality relating the quasiparticle decay rate to the density. The intercept of $\ensuremath{\gamma}$ vs $I$ yields the thermal equilibrium quasiparticle decay rate. In a discussion section, we argue that the quasiparticles induced by the laser occupy primarily states near the antinodal regions of the Brillouin zone. We explain the divergence of the lifetime of these particles as $T$ and $I$ both tend to zero as a consequence of momentum and energy conservation in electron-electron scattering. Next, we discuss the significance of the measured value of $\ensuremath{\beta}$, which is $\ensuremath{\approx}0.1\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{2}\phantom{\rule{0.3em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$ . We point out that the natural unit for $\ensuremath{\beta}$ in a two-dimensional superconductor is $\ensuremath{\hbar}∕{m}^{*}$, and define a dimensionless constant $C$ such that $\ensuremath{\beta}\ensuremath{\equiv}C\ensuremath{\hbar}∕{m}^{*}$. If the decay process is one in which quasiparticles return to the condensate with emission of a phonon, then $C$ is a measure of the electron-phonon interaction. Alternatively, expressing the marginal Fermi liquid scattering in the normal state in terms of an effective $\ensuremath{\beta}$ implies $C=1∕\ensuremath{\pi}$, which is in excellent agreement with the experimentally determined value in the superconducting state.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.023 | 0.002 |
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".