Charge Order Evolution of Superconducting BaNi2As2 Under High Pressure
Bibliographic record
Abstract
BaNi$_2$As$_2$, a non-magnetic superconductor counterpart to BaFe$_2$As$_2$, has been shown to develop nematic order, multiple charge orders, and a dramatic six-fold enhancement of superconductivity via isovalent chemical substitution of Sr for Ba. Here we present high pressure single-crystal and powder x-ray diffraction measurements of BaNi$_2$As$_2$ to study the effects of tuning lattice density on the evolution of charge order in this system. Single-crystal X-ray experiments track the evolution of the incommensurate (Q=0.28) and commensurate (Q=0.33 and Q=0.5) charge orders, and the tetragonal-triclinic distortion as a function of temperature up to pressures of 10.4 GPa, and powder diffraction experiments at 300 K provide lattice parameters up to 17 GPa. We find that applying pressure to BaNi$_2$As$_2$ produces a similar evolution of structural and charge-ordered phases as found as a function of chemical pressure in Ba$_{1-x}$Sr$_{x}$Ni$_2$As$_2$ , with coexisting commensurate charge orders appearing on increasing pressure. These phases also exhibit a similar abrupt cutoff at a critical pressure of (9 $\pm$ 0.5) GPa, where powder diffraction experiments indicate a collapse of the tetragonal structure at higher temperatures. We discuss the relationship between this collapsed tetragonal phase and the discontinuous phase boundary observed at the optimal substitution value for superconductivity in Ba$_{1-x}$Sr$_{x}$Ni$_2$As$_2$
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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 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 0.002 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.005 | 0.001 |
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".