High-resolution x-ray scattering studies of structural phase transitions in underdoped<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mi mathvariant="normal">La</mml:mi><mml:mrow><mml:mn>2</mml:mn><mml:mo>−</mml:mo><mml:mi>x</mml:mi></mml:mrow></mml:msub><mml:msub><mml:mi mathvariant="normal">Ba</mml:mi><mml:mi>x</mml:mi></mml:msub><mml:mi mathvariant="normal">Cu</mml:mi><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>4</mml:mn></mml:msub></mml:mrow></mml:math>
Bibliographic record
Abstract
We have studied structural phase transitions in high quality underdoped ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Ba}}_{x}\mathrm{Cu}{\mathrm{O}}_{4}$ single crystals using high-resolution x-ray scattering techniques. Critical properties associated with the continuous high temperature tetragonal (HTT) $(I4∕mmm)$ to middle temperature orthorhombic (MTO) $(Bmab)$ phase transition were investigated in single crystal samples with $x=0.125$, 0.095, and 0.08, and we find that all behavior is consistent with three-dimensional $XY$ criticality, as expected from theory. Power law behavior in the orthorhombic strain, $2(a\ensuremath{-}b)∕(a+b)$, is observed over a remarkably wide temperature range, spanning most of the MTO regime in the phase diagram. Low temperature measurements investigating the low temperature tetragonal (LTT) $(P{4}_{2}∕ncm)$ phase, below the strongly discontinuous $\mathrm{MTO}\ensuremath{\rightarrow}\mathrm{LTT}$ phase transition, in $x=0.125$ and $x=0.095$ samples show that the LTT phase is characterized by relatively broad Bragg scattering, compared with that observed at related wave vectors in the HTT phase. This shows that the LTT phase is either an admixture of tetragonal and orthorhombic phases or that it is orthorhombic with very small orthorhombic strain, consistent with the ``less orthorhombic'' low temperature structure previously reported in mixed ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x\ensuremath{-}y}{\mathrm{Ba}}_{y}\mathrm{Cu}{\mathrm{O}}_{4}$ single crystals. We compare the complex temperature-composition phase diagram for the location of structural and superconducting phase transitions in underdoped ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Ba}}_{x}\mathrm{Cu}{\mathrm{O}}_{4}$ and find good agreement with results obtained on polycrystalline samples.
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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 | 0.000 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 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".