Pressure effects on the superconducting transition in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>n</mml:mi><mml:mi>H</mml:mi><mml:mtext>-CaAlSi</mml:mtext></mml:mrow></mml:math>
Bibliographic record
Abstract
We present a combined experimental and theoretical study of the effects of pressure on ${T}_{c}$ of the hexagonal layered superconductors $nH\text{-CaAlSi}$ ($n=1$, 5, and 6), where $nH$ denotes the different stacking variants that were recently discovered. Experimentally, the pressure dependence of ${T}_{c}$ has been investigated by measuring the magnetic susceptibility of single crystals up to 10 kbars. In contrast to previous results on polycrystalline samples, single crystals with different stacking sequences display different pressure dependences of ${T}_{c}$. $1H\text{-CaAlSi}$ shows a decrease in ${T}_{c}$ with pressure, whereas $5H$- and $6H\text{-CaAlSi}$ exhibit an increase in ${T}_{c}$ with pressure. Ab initio calculations for $1H$-, $5H$-, and $6H\text{-CaAlSi}$ reveal that an ultrasoft phonon branch associated with out-of-plane vibrations of the Al-Si layers softens with pressure, leading to a structural instability at high pressures. For $1H\text{-CaAlSi}$, the softening is not sufficient to cause an increase in ${T}_{c}$, which is consistent with the present experiments but adverse to previous reports. For $5H$ and $6H$, the softening provides the mechanism to understand the observed increase in ${T}_{c}$ with pressure. Calculations for hypothetical $2H$ and $3H$ stacking variants reveal qualitative and quantitative differences.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.002 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.002 |
| Insufficient payload (model declined to judge) | 0.015 | 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; both teacher heads agree on what is shown here.
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".