Coupling of fully symmetric As phonon to magnetism in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>Ba</mml:mi><mml:msub><mml:mrow><mml:mo>(</mml:mo><mml:msub><mml:mi>Fe</mml:mi><mml:mrow><mml:mn>1</mml:mn><mml:mo>−</mml:mo><mml:mi>x</mml:mi></mml:mrow></mml:msub><mml:msub><mml:mi>Au</mml:mi><mml:mi>x</mml:mi></mml:msub><mml:mo>)</mml:mo></mml:mrow><mml:mn>2</mml:mn></mml:msub></mml:mrow><mml:msub><mml:mi>As</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math>
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Bibliographic record
Abstract
We study the coupling of the fully symmetric vibration mode of arsenic atoms to magnetism in a $\mathrm{Ba}{({\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Au}}_{x})}_{2}{\mathrm{As}}_{2}$ system by polarization-resolved Raman spectroscopy and neutron diffraction. In this system, there are two phase transitions: a tetragonal-to-orthorhombic structural phase transition at temperature ${T}_{S}$ and a magnetic phase transition into collinear spin-density wave (SDW) state at temperature ${T}_{N}$ ($\ensuremath{\le}{T}_{S}$). ${T}_{S}$ and ${T}_{N}$ almost coincide in the pristine compound, whereas they differ by as much as 8 K for compounds with dilute gold substitution for iron. Raman coupling to the ${A}_{g}$(As) phonon is forbidden for the $XY$ scattering geometry in the tetragonal phase above ${T}_{S}$, whereas it becomes allowed in the orthorhombic phase below ${T}_{S}$: The emerging mode's intensity indicates the lattice orthorhombicity. We find that upon cooling below ${T}_{S}$, first, weak ${A}_{g}$(As) phonon mode intensity appears in the $XY$ scattering geometry spectra; however, the mode's intensity is significantly enhanced in the magnetic phase below ${T}_{N}$. The ${A}_{g}$(As) phonon also shows an asymmetric line shape below ${T}_{N}$ and an anomalous linewidth broadening upon Au doping. We describe the anomalous behavior of the ${A}_{g}$(As) mode in the $XY$ scattering geometry using a Fano model involving the ${A}_{g}$(As) phonon interacting with the ${B}_{2g}({D}_{4h}$)-symmetry-like electron-hole continuum. We conclude that the temperature dependence of light coupling amplitude to the ${A}_{g}$(As) phonon follows the evolution of the magnetic order parameter $M(T)$. We propose that the intensity enhancement of the ${A}_{g}$(As) phonon in the $XY$ scattering geometry below ${T}_{N}$ is due to electronic anisotropy induced by the collinear SDW order parameter.
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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 | 0.011 | 0.017 |
| Meta-epidemiology (narrow) | 0.005 | 0.010 |
| Meta-epidemiology (broad) | 0.002 | 0.011 |
| Bibliometrics | 0.004 | 0.011 |
| Science and technology studies | 0.007 | 0.009 |
| Scholarly communication | 0.007 | 0.007 |
| Open science | 0.014 | 0.012 |
| Research integrity | 0.009 | 0.010 |
| Insufficient payload (model declined to judge) | 0.842 | 0.019 |
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 it