{"id":"42c440de-ff6f-4822-a856-3d91cf484528","arxiv_id":"2411.11025","paper_version":1,"verdict":"ACCEPT","confidence":"HIGH","novelty_score":2.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":6,"one_line_summary":"Antiferromagnetic perovskites with GdFeO3-type octahedral rotation are reviewed as altermagnets, giving spin-split bands, spin-current generation, and symmetry-selected anomalous Hall effects.","lead":"Many perovskite oxides and fluorides, usually classified as ordinary antiferromagnets, are argued to be altermagnets: their spin order combined with octahedral rotations produces spin-split bands and spin currents without spin-orbit coupling, and an anomalous Hall effect when spin-orbit coupling is added. This review collects the theoretical evidence and names specific compounds where these effects should be observable.","discovery_kind":"review","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The load-bearing risk is the rigid-octahedra tight-binding parametrization of the GdFeO3-type distortion: if the actual d-d hopping inequalities differ, the material-specific spin-current and AHE predictions in Table III could fail.","rationale":"The reader's weakest assumption correctly identifies the tight-binding parametrization as the main uncertainty. My independent reading reaches the same conclusion: the symmetry arguments (Table II) are robust, but the bridge from generic symmetry to specific materials is the microscopic hopping pattern in Figs. 3(c)-3(e), which is not checked against ab initio results for the candidate perovskites. This concern does not undermine the review's value as a synthesis of existing theoretical work; the underlying model calculations are self-consistent and reproduce early first-principles findings (Refs. [28-30]). The risk is that the quantitative predictions for real materials—spin-current sign, magnitude, and the exact AHE component—may not survive a realistic parametrization. A DFT Wannier-function test for one representative compound, CaCrO3, would settle whether the assumed hopping inequalities hold. I therefore keep the verdict unchanged: the review is acceptable, with the caveat already noted by the reader. The concern is load-bearing but not fatal, because the paper is a review of a theoretical mechanism, not a claim of experimental verification.","tokens_in":15611,"tokens_out":7182,"duration_ms":107949,"concrete_test":"Perform DFT+U calculations for CaCrO3 in the experimental Pbnm structure (B-X-B angle ≈160°); construct maximally-localized Wannier functions for the Cr t2g bands; extract the NN and NNN hopping integrals in the local x'y'z' basis. Verify the direction-dependent inequalities of Figs. 3(c)-3(d) (z'x'(B1)-x'y'(B2) along [1-10] > y'z'(B1)-x'y'(B2) along [110], with the opposite on B2-B1 bonds). Then compute the spin-current conductivity χxy from the Wannier-interpolated bands using Boltzmann transport with a constant relaxation time and compare sign and magnitude with the model result at φ≈25°. If the extracted hoppings or χxy differ qualitatively, the paper's material-specific claim for CaCrO3 fails.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The review's central claim—that distorted perovskites with C-type AFM order exhibit non-relativistic spin splitting, spin-current generation, and SOC-induced AHE—rests on the microscopic model of Sec. III, Eq. (1). The model's key ingredient is the sublattice-dependent anisotropic NN and NNN d-d transfer integrals generated by the GdFeO3-type distortion, shown in Figs. 3(c)-3(d), with the tilt angle ψ fixed by the rotation angle φ (Ref. [32]). These integrals are not validated against first-principles calculations for the specific candidate compounds; they are derived from a rigid-octahedra geometric construction using ligand p-orbital mediation. Real perovskites have independent rotation and tilting amplitudes, A-site dependence, and possible Jahn-Teller distortions that are not captured by a single-parameter geometry. If, e.g., in CaCrO3 the inter-orbital hoppings between z'x'(B1) and x'y'(B2) along [1-10] are not larger than those between y'z'(B1) and x'y'(B2) along [110] (and vice versa on B2-B1-B2 bonds), the d-wave spin splitting and the sign of the spin-current conductivity χxy could change or vanish. The symmetry analysis in Table II and Sec. VI would remain valid, but the material-specific predictions in Table III would lose quantitative support. This is the weakest load-bearing point because the qualitative existence of altermagnetic behavior is symmetry-protected, while the candidate assignment depends on the tight-binding parametrization.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"This manuscript reviews the authors' and others' theoretical work on altermagnetism in perovskite-structure oxides, with emphasis on the microscopic mechanism by which GdFeO3-type octahedral rotations combine with collinear antiferromagnetic order (particularly C-type order in d2 systems) to produce non-relativistic spin splitting and electric-field-driven spin currents, and, in the presence of spin-orbit coupling, component-specific anomalous Hall effects. The review introduces a multiorbital Hubbard model with nearest- and next-nearest-neighbor ligand-mediated d-d hoppings, summarizes model results for the C-type antiferromagnetic phase, establishes a symmetry-based selection rule for the anomalous Hall effect in the four AFM patterns compatible with Pbnm symmetry (Table II), and compiles a candidate-material table with predicted cross-correlation phenomena (Table III).","tokens_in":15921,"tokens_out":7475,"duration_ms":86461,"significance":"The review's main contribution is a clear synthesis: the symmetry-based Table II connects the four allowed AFM patterns in the Pbnm perovskite structure to the corresponding anomalous Hall conductivity components, and it is consistent both with the earlier ab initio results of Solovyev (Ref. [30]) and with the authors' own model calculations. The paper also makes a useful pedagogical point by separating the symmetry-allowed existence of spin splitting and AHE from the model-dependent microscopic mechanisms (anisotropic sublattice-dependent hoppings for spin currents; next-nearest-neighbor triangular-loop fictitious flux for the AHE). The candidate table (Table III) provides a practical guide for experimental searches. A notable strength is that the model calculations are parameter sweeps rather than circular fits, so they yield falsifiable predictions (nonzero χ_xy in metallic C-type AFM phases, σ_yz in the FxCyGz state, and so on). The main limitation is that the quantitative magnitudes and signs of χ_xy and σ_yz are derived from a rigid-octahedra tight-binding parametrization (Sec. III, Eq.","major_comments":[],"minor_comments":[{"comment":"The abstract contains the typo \"Altermagneticsm\" and the main text contains several misspellings (e.g., \"orbtial\" in Sec. I, \"perovkite\" in Sec. I, \"interation\" in Sec. IV, \"canditate\" in Sec. VII, \"comoponents\" in the Table III caption, \"electic\" in Sec. VIII); these should be corrected.","section":"Abstract and throughout"},{"comment":"The notation \"NN∑\" and \"NNN∑\" is unconventional and potentially confusing; please replace it with standard sums over nearest-neighbor and next-nearest-neighbor pairs, such as Σ_{⟨ij⟩} and Σ_{⟨⟨ij⟩⟩}, with a brief definition.","section":"Sec. III, Eq. (1)"},{"comment":"The statement that \"the additional tilting ψ is uniquely determined by φ [32]\" is a strong geometric simplification; real perovskites often exhibit independent rotation and tilting amplitudes, so the manuscript should specify the assumed Glazer tilt system or justify why a single-parameter description is adequate for the model.","section":"Sec. III, after Eq. (1)"},{"comment":"Please replace \"constantly zero\" with \"identically zero\" when describing χ_xy at φ = 0, and clarify that the displayed χ_xy values are model results for a representative parameter set, not first-principles predictions.","section":"Sec. V, Fig. 5"},{"comment":"The definition of the tilde quantities (σ̃_yz and σ̃_zx) is given only in the text; the caption of Fig. 6(a) should also state that these are obtained by artificially keeping only the major collinear AFM component in the mean-field solution.","section":"Sec. VI, Fig. 6"},{"comment":"The table caption says \"whose deviation from 180° indicates the degree of the GdFeO3-type distortion,\" but for A-site-substituted compounds the B-X-B angle depends on composition; please state the composition to which each listed angle refers or note that the angle is representative.","section":"Sec. VII, Table III"},{"comment":"Reference [68] lists the authors \"A. Birk Hellenes\" and \"Z. Jansa\" twice each; please correct the author list.","section":"References"},{"comment":"The manuscript would benefit from an explicit caveat that the quantitative values (magnitudes and signs) of the spin-current conductivity and anomalous Hall conductivity shown in Figs. 5 and 6 are model-dependent and may be revised by future first-principles calculations; the qualitative existence and the choice of tensor components follow from symmetry and are the robust predictions.","section":"Sec. VII and Summary"}],"recommendation":"minor_revision","confidential_remarks":"The review is heavily based on the authors' own previous papers (Refs. [5] and [6]) and covers the general literature mainly in the introduction and the candidate table; for a journal with a strong review tradition, the editors may wish to ensure that the scope is framed as a mechanism-focused review of the authors' model work rather than a fully comprehensive survey of altermagnetic perovskites. This is not a technical flaw, but it affects the reader's expectation. The technical content is sound and the symmetry analysis is a worthwhile synthesis."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Short version: this is a review, not a new-results paper, and it says so. The value is in the synthesis: it connects the early first-principles work of Solovyev and Okugawa et al. to the authors' own Hubbard-model calculations, and boils the altermagnetic response down to a clean symmetry table (Table II). That table is internally consistent and matches the earlier ab initio AHE results, so the central classification argument holds up.\n\nWhat's actually new here is the packaging: a systematic candidate list (Table III) that maps AFM patterns in distorted perovskites onto spin-current and AHE expectations. That's useful for experimentalists. The paper is honest about its own status and about the fact that the spin-current mechanism was predicted in the authors' earlier PRB papers. Self-citation in that context is legitimate; those papers contain parameter sweeps and falsifiable predictions, not fittings of the target result.\n\nSoft spots, in proportion: the quantitative predictions for spin-current conductivity and AHE magnitude rest on the tight-binding parametrization of the GdFeO3 distortion, specifically the sublattice-dependent inter-orbital hoppings in Sec. III. That's a real limitation. The symmetry argument is robust, but the signs and magnitudes in Table III could change if the rigid-octahedra geometry with a single tilt angle miscalculates the actual d-d overlaps. The stress-test note is right about that being the weakest load-bearing point. It's not fatal for a review, because the qualitative altermagnetic behavior is symmetry-protected and the authors say the table is non-exhaustive, but readers should treat the specific compounds as candidates, not confirmed predictions. Also, there's no direct experimental confirmation of spin currents in these perovskites yet; the paper notes that.\n\nWho's this for? Experimentalists working on perovskite oxides and people entering the altermagnetism literature. A serious referee should engage with the symmetry table and check the model-to-material mapping; the paper deserves review rather than desk rejection. My own verdict: send it to review, with the expectation that the authors tighten the discussion of the tight-binding uncertainty.","headline":"A solid, honest review that reclassifies known perovskite antiferromagnets as altermagnetic candidates; the symmetry framework is the real value, the quantitative table is softer.","tokens_in":16509,"tokens_out":1533,"would_cite":true,"duration_ms":17519,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"Perovskites with the common GdFeO3-type octahedral rotation are predicted to be altermagnets, exhibiting spin-split bands and spin-current generation without spin-orbit coupling, and a component-specific anomalous Hall effect with it.","keywords":["altermagnetism","perovskite oxides","antiferromagnet","spin current","anomalous Hall effect","GdFeO3-type distortion","Hubbard model","spin-orbit coupling"],"falsifier":"Measure the spin current conductivity in CaCrO3 (C-type antiferromagnetic metal, $T_N \\approx 90$ K) by applying an electric field along [010] and detecting the transverse spin current along [100]: the predicted symmetric tensor ($\\chi_{xy} = \\chi_{yx}$, $\\chi_{xx} = \\chi_{yy} = 0$) and its scaling with the longitudinal conductivity distinguish this mechanism from the spin Hall effect, and their absence below $T_N$ would refute the model.","tokens_in":1959,"feed_emoji":"🧲","tokens_out":3026,"duration_ms":82344,"temperature":0.7,"pith_summary":"This review argues that the standard octahedral rotation found in most perovskite oxides — the GdFeO3-type distortion — turns many antiferromagnetic perovskites into altermagnets, a class of magnets with zero net magnetization but broken time-reversal symmetry. Working from a multi-orbital Hubbard model, the authors show that the rotation makes electron hoppings sublattice-dependent and spatially anisotropic, which together with a C-type antiferromagnetic order produces non-relativistic spin-split bands. In the metallic state these bands generate a spin current under an applied electric field without any spin-orbit coupling. When spin-orbit coupling is included, the same distorted structure gives a component-specific anomalous Hall effect that can be read off from the broken mirror and glide symmetries. A sympathetic reader would care because it predicts concrete, measurable cross-correlation phenomena in well-known compounds such as CaCrO3 and LaVO3.","feed_headline":"A common octahedral twist turns perovskites into altermagnets","feed_subtitle":"Model predicts spin currents without spin-orbit coupling and pinpoints which planes show anomalous Hall effect.","key_machinery":"The load-bearing object is the multi-d-orbital Hubbard model on the distorted perovskite lattice, with transfer integrals evaluated through ligand p orbitals for a rigid-octahedra geometry parametrized by the rotation angle $\\varphi$ (the GdFeO3-type distortion). Its key output is the pattern of nearest-neighbor inter-orbital hoppings that are sublattice-dependent — switched between the $[110]$ and $[1\\bar{1}0]$ directions on the B1 versus B2 bonds — plus next-nearest-neighbor hoppings through the ligands. The former produce the non-relativistic spin splitting and spin current; the latter, together with spin-orbit coupling, produce the fictitious magnetic flux loops that generate the anomalous Hall effect. A symmetry rule — the anomalous Hall component is fixed by which two of the three mirror and glide operations are broken by the magnetic order — carries the classification in Table II.","core_discovery":"The central claim is that altermagnetism is latent in the perovskite family: the GdFeO3-type distortion, present in many ABX3 compounds, makes the inter-orbital d-d transfer integrals sublattice-dependent and anisotropic in the specific pattern shown for the B1-B2 bonds, so that when the antiferromagnetic order breaks time-reversal symmetry, the band structure acquires a d-wave-like spin splitting even at zero spin-orbit coupling. This splitting yields a spin current conductivity with a symmetric tensor ($\\chi_{xy} = \\chi_{yx}$, diagonal elements zero) in the C-type antiferromagnetic metallic phase. With spin-orbit coupling, the next-nearest-neighbor hoppings through ligand p orbitals generate a net fictitious magnetic field along one axis, giving an anomalous Hall effect in the perpendicular plane; the rules are summarized in Table II, where breaking two of the three mirror and glide symmetries selects which Hall component is active. The authors therefore assert that the mechanism does not rely on spin-orbit coupling for the spin current, and that the anomalous Hall effect is driven by the collinear antiferromagnetic component with the same symmetry as the weak ferromagnetism, not by the net moment itself.","pith_inferences":["If the mechanism holds for the listed compounds, many previously ordinary antiferromagnetic perovskites — including doped manganites and ferrites — would be reclassified as altermagnetic candidate materials, and past transport data might already contain unread spin-current or Hall signals.","The same orbital-overlap logic suggests that layered Ruddlesden-Popper perovskites and 4d/5d systems, which also exhibit octahedral rotations, may show altermagnetic responses with altered anisotropy patterns, a testable extension beyond the paper's explicit list.","A direct experimental test would be spin- and angle-resolved photoemission on a cleaved CaCrO3 or LaVO3 surface below $T_N$: the predicted d-wave spin splitting should vanish on the $k_x=0$ and $k_y=0$ mirror planes, a signature not present in conventional Néel antiferromagnets.","The proximity-effect anomalous Hall effect already observed at interfaces of distorted perovskites could be interpreted as the present altermagnetic Hall effect combined with scalar spin chirality, an idea the authors flag as awaiting further analysis."],"forward_implications":["CaCrO3 and LaVO3, which show C-type antiferromagnetic order and GdFeO3-type distortion, are predicted to exhibit electric-field-driven spin currents in their metallic antiferromagnetic phases.","Several orthorhombic perovskites (for example LaCrO3, YCrO3, LaFeO3, and doped manganites) are predicted to show anomalous Hall conductivity in specific planes selected by their antiferromagnetic pattern, such as $\\sigma_{xy}$ for $G_xA_yF_z$ and $\\sigma_{yz}$ for $F_xC_yG_z$.","The spin-current generation is a dissipative effect whose conductivity should scale with the longitudinal electrical conductivity below the Néel temperature, distinguishing it from the spin Hall effect.","The anomalous Hall effect can appear even when the net magnetization is zero, because a single collinear antiferromagnetic component that breaks the required symmetries is sufficient.","The symmetry rule extends beyond perovskites to the organic altermagnet $\\kappa$-(ET)2X, which belongs to the same space group Pbnm."],"supporting_citations":[{"why":"Provides the multi-orbital Hubbard model calculation for the spin current conductivity and the phase diagram in the (3d)2 case.","marker":"[5]"},{"why":"Supplies the model result for the anomalous Hall effect and the fictitious-field mechanism in C-type antiferromagnetic perovskites.","marker":"[6]"},{"why":"Introduces the spin-current mechanism in organic altermagnets that the perovskite analysis is modeled on.","marker":"[8]"},{"why":"Independent proposal of non-relativistic spin splitting and spin current in RuO2, used as a comparative altermagnet.","marker":"[12]"},{"why":"Proposal of the anomalous Hall effect in altermagnetic RuO2, establishing the spin-orbit-coupling-based counterpart.","marker":"[13]"},{"why":"Early first-principles calculation of the optical Hall conductivity in orthorhombic LaBO3 perovskites, which the present anomalous Hall analysis reproduces and explains.","marker":"[30]"},{"why":"First-principles report of spin-split band structures without spin-orbit coupling in perovskite antiferromagnets, which the model reproduces.","marker":"[29]"},{"why":"Defines altermagnetism and the symmetry conditions, used to classify the perovskite magnetic patterns.","marker":"[7]"},{"why":"Provides the geometric relation between the rotation angle and tilting angle used to parametrize the GdFeO3-type distortion.","marker":"[32]"}],"fun_headline_variants":["Octahedral twist altermagnetizes perovskites","A simple twist turns perovskites into altermagnets","Perovskite twist yields spin currents sans spin-orbit","Common distortion makes altermagnetic perovskites","Twist-induced altermagnetism in perovskites"],"cache_read_input_tokens":18560,"weakest_assumption_plain":"The mechanism depends on the tight-binding parametrization in which the rotated octahedra fix the orbital overlaps through ligand p orbitals with a rigid-octahedra geometry; if the real orbital overlap pattern differs, the predicted spin splitting, spin-current sign, and Hall selection rules could fail even though the symmetry analysis remains formally correct.","fun_headline_variants_meta":{"raw":{"variants":["Octahedral twist altermagnetizes perovskites","A simple twist turns perovskites into altermagnets","Perovskite twist yields spin currents sans spin-orbit","Common distortion makes altermagnetic perovskites","Twist-induced altermagnetism in perovskites"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.00086,"raw_usage":{"total_tokens":3803,"prompt_tokens":1086,"completion_tokens":2717,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":702,"completion_tokens_details":{"reasoning_tokens":2642}},"tokens_in":702,"tokens_out":2717,"duration_ms":22079,"temperature":1.0,"reasoning_tokens":2642,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-12T19:01:29.814054+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure the spin current conductivity in CaCrO3 (C-type antiferromagnetic metal, $T_N \\approx 90$ K) by applying an electric field along [010] and detecting the transverse spin current along [100]: the predicted symmetric tensor ($\\chi_{xy} = \\chi_{yx}$, $\\chi_{xx} = \\chi_{yy} = 0$) and its scaling with the longitudinal conductivity distinguish this mechanism from the spin Hall effect, and their absence below $T_N$ would refute the model.","supporting_citations":[{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Provides the multi-orbital Hubbard model calculation for the spin current conductivity and the phase diagram in the (3d)2 case."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Supplies the model result for the anomalous Hall effect and the fictitious-field mechanism in C-type antiferromagnetic perovskites."},{"cited_title":"Maekawa, T","cited_arxiv_id":null,"evidence_quote":"Introduces the spin-current mechanism in organic altermagnets that the perovskite analysis is modeled on."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Independent proposal of non-relativistic spin splitting and spin current in RuO2, used as a comparative altermagnet."},{"cited_title":"ˇSmejkal, R","cited_arxiv_id":null,"evidence_quote":"Proposal of the anomalous Hall effect in altermagnetic RuO2, establishing the spin-orbit-coupling-based counterpart."},{"cited_title":"For example, MnTe is proposed to belong to “ g-wave” altermagnets that do not show spin current generation","cited_arxiv_id":null,"evidence_quote":"Early first-principles calculation of the optical Hall conductivity in orthorhombic LaBO3 perovskites, which the present anomalous Hall analysis reproduces and explains."},{"cited_title":"Okugawa, K","cited_arxiv_id":null,"evidence_quote":"First-principles report of spin-split band structures without spin-orbit coupling in perovskite antiferromagnets, which the model reproduces."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Provides the geometric relation between the rotation angle and tilting angle used to parametrize the GdFeO3-type distortion."}],"review_version":1}