XY magnetism, Kitaev exchange, and long-range frustration in the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>J</mml:mi><mml:mi>eff</mml:mi></mml:msub><mml:mo>=</mml:mo><mml:mfrac><mml:mn>1</mml:mn><mml:mn>2</mml:mn></mml:mfrac></mml:math> honeycomb cobaltates
Bibliographic record
Abstract
The quest for Kitaev quantum spin liquids has led to great interest in honeycomb quantum magnets with strong spin-orbit coupling. It has been recently proposed that even Mott insulators with $3d$ transition-metal ions, having nominally weak spin-orbit coupling, can realize such exotic physics. Motivated by this, we study the rhombohedral honeycomb cobaltates ${\mathrm{CoTiO}}_{3},$ ${\mathrm{BaCo}}_{2}{({\mathrm{PO}}_{4})}_{2}$, and ${\mathrm{BaCo}}_{2}{({\mathrm{AsO}}_{4})}_{2}$, using ab initio density-functional theory, which takes into account realistic crystal-field distortions and chemical information, in conjunction with exact diagonalization numerics. We show that these ${\mathrm{Co}}^{2+}$ magnets host ${J}_{\mathrm{eff}}=1/2$ local moments with highly anisotropic $g$ factors, and we extract their full spin Hamiltonians including longer-range and anisotropic exchange couplings. For ${\mathrm{CoTiO}}_{3}$, we find a nearest-neighbor easy-plane ferromagnetic $XXZ$ model with additional bond-dependent anisotropies and interlayer exchange, which supports three-dimensional Dirac nodal line magnons. In contrast, for ${\mathrm{BaCo}}_{2}{({\mathrm{PO}}_{4})}_{2}$ and ${\mathrm{BaCo}}_{2}{({\mathrm{AsO}}_{4})}_{2}$, we find a strongly suppressed interlayer coupling, and significant frustration from additional third-neighbor antiferromagnetic exchange mediated by P or As. Such bond-anisotropic ${J}_{1}\text{\ensuremath{-}}{J}_{3}$ spin models can support collinear zigzag or coplanar spiral ground states. We discuss their dynamical spin correlations which reveal a gapped Goldstone mode and argue that the effective parameters of the pseudospin-$1/2$ models in these two materials may be strongly renormalized by coupling to a low-energy spin exciton. Our results call for reexamining proposals for realizing Kitaev spin liquids in the honeycomb cobaltates.
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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 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| 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".