{"id":"f2a3a35f-4ee6-4dc2-be13-4f035639440f","arxiv_id":"2608.06737","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":3,"one_line_summary":"A new bulk magnet, Eu3In2As4, combines very strong exchange coupling with soft magnetism, letting modest fields and field orientation switch the material among topological-insulator, ferrimagnetic, Weyl-semimetal, and nodal-ring states.","lead":"Eu3In2As4 crystals show magnetization-dependent electronic band shifts up to 300 meV, far beyond ordinary Zeeman splitting, and reach full magnetic polarization in fields around 1 T. The authors map a field-driven sequence from an antiferromagnetic topological insulator to a proposed ferrimagnetic phase and fully polarized states predicted to be minimal Weyl or nodal-ring semimetals.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Experimental Fermi level from SdH sits ~0.155 eV above the DFT Fermi level and 'away from the Weyl points,' so the headline minimal-Weyl state is not the measured state but a prediction at a different filling.","rationale":"I agree with the reader's CONDITIONAL verdict but not with the primary weakest assumption. The reader identifies the 2/3-FiMa phase as the load-bearing assumption; that is a legitimate concern, and the paper itself flags the need for neutron diffraction. However, the more central issue is that the measured Fermi level, as determined by the authors' own SdH analysis, is about 0.155 eV above the DFT Fermi level and is described as being 'away from the Weyl points.' This directly undercuts the headline claim of a realized minimal Weyl semimetal with vectorially tunable nodes. The exchange-driven band shifts themselves are supported by multiple consistent probes and can be accepted; the overreach is in presenting the calculated Weyl phase as the state of the measured material. The concrete test I propose would settle whether the Weyl nodes are actually near the experimental Fermi level or only exist at a different filling. If they are away from EF, the paper should be conditionally accepted with major revision: reframe the Weyl state as a tunable prediction requiring charge-neutral samples, and add the missing magnetic-structure verification for the intermediate phase.","tokens_in":24353,"tokens_out":9421,"duration_ms":93805,"concrete_test":"Using the same DFT+U (Ueff = 7 eV) and Wannier setup, compute at the experimentally determined chemical potential EF_DFT + 0.155 eV: (1) the energies of all Weyl nodes relative to this EF; (2) the Fermi surface at this EF; and (3) the intrinsic anomalous Hall conductivity at this EF. If the Weyl nodes lie more than a few meV away from this EF, or if additional trivial bands cross the Fermi level at this energy, then the 'minimal Weyl semimetal free from extraneous band complications' claim is not realized in the as-grown crystals, and the paper should be revised to present the Weyl state as a charge-neutrality prediction requiring Fermi-level tuning.","verdict_should_be":"CONDITIONAL","load_bearing_attack":"The paper's strongest claim is that fully polarized Eu3In2As4 is a minimal Weyl semimetal with a single pair of Weyl nodes and no extraneous bands at the Fermi level. Section 2.4 shows that the experimental Fermi level is determined by matching the SdH frequency to DFT, yielding a value approximately 0.155 eV above the DFT Fermi energy and 'placing it above the Lifshitz transition.' The same section later states that the measured AHE is insensitive to Weyl-cone evolution 'likely due to the high electron density and the large Fermi pocket being away from the Weyl points.' Thus the actual as-grown crystals are not at the filling where the ideal Weyl state is predicted: the Weyl nodes are not at the chemical potential, and transport is dominated by a large electron pocket away from the nodes. This is not merely a missing direct spectroscopic verification; it is an internal mismatch between the claimed realized state and the measured doping. The vectorial tunability of Weyl-node positions, central to the title and abstract, is therefore a DFT prediction at a different Fermi level rather than a property demonstrated in the measured material. Even if the 2/3-FiMa phase were confirmed by neutron diffraction, this Fermi-level mismatch would remain. The paper should be reframed as a prediction requiring Fermi-level tuning toward charge neutrality, and the current 'minimal Weyl semimetal' wording overstates the experimental realization.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"The manuscript reports a combined experimental and DFT study of the magnetic topological material Eu3In2As4. It claims that the compound exhibits exchange-driven band shifts up to ~300 meV, which it interprets as a giant exchange coupling between Eu 4f moments and itinerant carriers. From magnetization, magneto-infrared spectroscopy, anisotropic magnetoresistance, Shubnikov–de Haas oscillations, and anomalous Hall effect, together with DFT+U and Wannier-based band-structure calculations, the paper constructs a field-temperature phase diagram that includes an AFM topological-insulator ground state, a proposed 2/3-ferrimagnetic intermediate phase, and fully polarized FM states predicted to host a minimal Weyl semimetal with a single pair of Weyl nodes, or a nodal-ring semimetal for magnetization along c. The paper argues that the momentum-space positions of the Weyl nodes can be tuned by rotating the magnetization direction.","tokens_in":24660,"tokens_out":2479,"duration_ms":27072,"significance":"If the central claims hold, Eu3In2As4 would be a valuable platform: it combines a simple, nearly isotropic Fermi surface with a very large exchange-driven band reconstruction and soft magnetism, which are rarely found together. The paper deserves credit for the breadth of independent measurements (magnetization, magneto-IR, AMR, SdH, AHE) that mutually support exchange-driven band reconstruction, and for being explicit in the Conclusions that the topological assignments rely primarily on calculations and that direct Weyl-cone spectroscopy and Fermi-level tuning remain future work. The DFT calculations are also reported with concrete parameters and verified with WannierTools. However, two load-bearing points — the experimental Fermi level relative to the predicted Weyl nodes, and the inference of the 2/3-FiMa phase from magnetization derivatives alone — currently leave the headline 'minimal Weyl semimetal' as a prediction at a different filling rather than a demonstrated property of the as-grown crystals.","major_comments":[{"comment":"The SdH analysis places the experimental Fermi level approximately 0.155 eV above the DFT Fermi energy, which the authors state is above the Lifshitz transition. In the same section they note that the measured AHE is insensitive to Weyl-cone evolution 'likely due to the high electron density and the large Fermi pocket being away from the Weyl points.' This is an internal mismatch between the claimed realized minimal-Weyl state and the measured doping: the transport and quantum-oscillation data are dominated by a large electron pocket that is not at the Weyl nodes. The abstract's statement that the fully polarized state 'is predicted to host either Weyl or nodal-ring semimetals' is careful, but the paper's title, abstract, and Section 2.1 nevertheless present the material as if the minimal Weyl phase were realized. This mismatch should be reframed as a prediction requiring Fermi-level tuning toward charge neutrality, or the authors must provide evidence that the measured Fermi level nevertheless samples the Weyl physics in a meaningful way.","section":"§2.4"},{"comment":"Equation (3) is used to extract effective exchange constants Jeff from the slopes of transition-energy versus magnetization curves, and the same data are then presented as evidence that the transition energies scale linearly with M. This is partly circular: the linear scaling is assumed from the mean-field Heisenberg model, not independently predicted. Moreover, the approximately 500 meV exchange splitting for the middle band is obtained from the simplified three-band assignment of Tα, Tβ, Tγ to LB→MB and LB→UB transitions, which is an ad-hoc model that neglects SOC and antiferromagnetic exchange. The paper should clearly state which parts of the 'scaling' are fits, and ideally validate the assignment with a different probe (e.g., temperature dependence, doping series, or comparison at two geometries) or by explicitly showing that alternative assignments are excluded.","section":"§2.2, Eq. (3)"},{"comment":"The proposed 2/3-FiMa intermediate phase is load-bearing for the topological-evolution narrative (AFM TI → FiM → FM Weyl), but its microscopic spin configuration is inferred only from magnetization and derivative analyses. The authors acknowledge that a definitive determination would require neutron diffraction or related probes. In the absence of such a determination, the phase diagram in Figure 1g is not established beyond speculation. The DFT support in Table S3 uses a specific collinear configuration and Ueff = 7 eV, which does not by itself establish that the real material realizes sequential polarization of Eu1 then Eu2. This caveat should be moved from a sentence to a clearly visible limitation, and the word 'proposed' should be used consistently throughout the abstract and main text.","section":"§2.1, Figure 1g"}],"minor_comments":[{"comment":"The notation for the exchange constant is inconsistent: Equation (1) defines Jex, while Equation (3) and the surrounding text use Jeff; the definition of Jeff as the 'net exchange contribution of the two participating bands' should be stated more explicitly and used consistently.","section":"§2.2"},{"comment":"The phase labels cAFM-1 and cAFM-2 are introduced in the text and Figure 1g but are not consistently defined in the figure caption or a table; a short list of all magnetic phases with their distinguishing features would improve readability.","section":"§2.1"},{"comment":"The caption states that the Fermi surface is plotted at E-EF = 0.155 eV, which is the value matched to the SdH frequency; however, the main text does not clearly state that this value is an experimental input rather than a DFT prediction, which could mislead readers about the origin of the Fermi-level offset.","section":"Figure 4d"},{"comment":"The Conclusions correctly list the limitations, but the abstract and Section 1 do not. For a paper whose central claim is a 'minimal topological magnet,' the abstract should reflect the same degree of caution about the Weyl-phase realization at the actual Fermi level.","section":"§4"}],"recommendation":"major_revision","confidential_remarks":"The manuscript is a strong candidate for a high-impact journal if the central claims are properly scoped. The main risk is overclaiming the experimental realization of the minimal Weyl state when the measured Fermi level sits away from the Weyl nodes. The Fermi-level mismatch and the inferred 2/3-FiMa phase are fixable by reframing the paper as a combined prediction and evidence for exchange-driven band reconstruction, with the Weyl-node tuning presented as a theoretical prediction requiring Fermi-level control. The circularity concern with Eq. (3) is also addressable by explicitly labeling the fits and adding a sensitivity analysis. I would not reject the manuscript; the experimental dataset is unusually comprehensive for a newly predicted topological magnet."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Two things to know. First, the magneto-infrared data showing ~300 meV field-driven band shifts in Eu3In2As4 are genuine, and the supporting magnetization, AMR, SdH, and AHE data are mutually consistent. This is a well-executed experimental study. Second, the 'minimal Weyl semimetal' in the title and abstract is not the state measured in these crystals. The SdH analysis puts the Fermi level ~0.155 eV above the DFT Fermi energy, above the Lifshitz transition, and the authors themselves note the large electron pocket is away from the Weyl points. The vectorial Weyl control is a DFT prediction at a different filling, not a demonstrated property.\n\nThe genuinely new content is the first bulk single-crystal experimental work on this Zintl compound. The exchange-driven band reconstruction is unusually large and clean, and the multi-probe consistency is a real strength. The paper also gives honest caveats: the 2/3-FiMa phase is inferred from magnetization derivatives only, and direct Weyl spectroscopy and transport near charge neutrality are left to future work.\n\nThe soft spots are real but not disqualifying. The Fermi-level mismatch is the main one: the measured π-Berry phase and AHE in the FM state are not clean probes of the Weyl nodes. The exchange parameters in Eq. (3) are fitted to the same magneto-IR data used to claim the giant exchange, so the ~500 meV exchange splitting is model-dependent. The 2/3-FiMa phase and the associated topological evolution narrative rest on magnetization derivatives and DFT, not a confirmed magnetic structure. None of these issues sink the paper, but they mean the headline claims should be reframed as predictions awaiting Fermi-level tuning and neutron diffraction.\n\nThis paper is for condensed-matter researchers working on magnetic topological materials, Eu-based Zintls, or exchange-driven band engineering. It deserves serious peer review. A referee should request a clear separation of measured results from predicted states, and a toned-down abstract. If the authors revise along those lines, I would support conditional acceptance.","headline":"The experimental band-shift data are strong, but the as-grown crystals sit at a Fermi level away from the predicted Weyl nodes, so the 'minimal Weyl semimetal' is a prediction, not a realized state.","tokens_in":25275,"tokens_out":4202,"would_cite":true,"duration_ms":40532,"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":"Eu3In2As4 is a minimal Weyl semimetal whose single pair of Weyl nodes can be steered by rotating the magnetization, driven by exchange coupling that shifts bands by up to 300 meV.","keywords":["exchange coupling","ideal Weyl semimetal","topological phase transition","topological magnet","Eu3In2As4","spin-flop transition","magneto-infrared spectroscopy","anomalous Hall effect"],"falsifier":"Neutron diffraction on a single crystal at 1.8 K with field along the a-axis near the 2/3-Msat plateau would settle the intermediate phase: if the Eu1 sublattice is fully polarized while Eu2 retains antiferromagnetic order the sequential scenario holds, whereas simultaneous canting of both sublattices with no distinct plateau would invalidate it; separately, angle-resolved photoemission on the fully polarized state should reveal exactly one Weyl pair at the predicted kx-ky momenta, with any extra Fermi-surface crossings or trivial pockets refuting the minimal-Weyl claim.","tokens_in":24112,"feed_emoji":"🧲","tokens_out":7729,"duration_ms":70522,"temperature":0.7,"pith_summary":"This paper reports that the layered Zintl compound Eu3In2As4 combines a giant exchange coupling between localized Eu2+ moments and itinerant electrons with a soft, easily rotated magnetization. The authors identify magnetization-dependent band shifts of up to 300 meV, far beyond ordinary Zeeman scales, and use them to map a sequence of magnetic phases: an antiferromagnetic topological-insulator ground state, a proposed 2/3-ferrimagnetic intermediate phase, and fully polarized states. In the fully polarized phase the compound is predicted to be a minimal Weyl semimetal, hosting a single pair of Weyl nodes with no extraneous bands at the Fermi level. The paper argues that rotating the magnetization direction moves the Weyl nodes in momentum space, making Eu3In2As4 a platform for vectorial control of topological band structure.","feed_headline":"Rotating the magnetization steers a lone Weyl pair in Eu3In2As4","feed_subtitle":"Giant exchange coupling shifts bands by up to 300 meV, so rotating the field steers the material's Weyl nodes.","key_machinery":"The load-bearing mechanism is the spin-only Heisenberg exchange between localized Eu2+ 4f7 moments (S = 7/2, L = 0) and itinerant carriers, Hex = -2Jex Σ si·Si. Under a mean-field approximation the exchange-induced band shift is proportional to the reduced magnetization M(T,B)/Msat, so that measured optical transition energies obey ΔE = -(1/2) Jeff S M/Msat; this proportionality is the identity that converts magnetization curves into predicted band-structure changes. A secondary structural ingredient is the presence of two inequivalent Eu sublattices with multiplicity ratio 2:1, which is used to propose a sequential polarization scenario in which the larger sublattice polarizes first, producing an intermediate 2/3-ferrimagnetic phase before the second sublattice flops.","core_discovery":"On the paper's own terms, the central discovery is a material in which exchange coupling, rather than external field strength, dominates the electronic structure: aligning the Eu2+ moments with fields of about 1 T shifts optical transition energies by hundreds of meV, and this exchange-driven reconstruction transforms the ground state from an axion-insulator-like antiferromagnet into a semimetal. When the moments are fully polarized along the a or b axis, first-principles calculations show exactly one pair of Weyl nodes in the kx-ky plane, with no trivial bands crossing the Fermi level, the minimal Weyl configuration possible. Magnetization along c instead stabilizes an ideal nodal-ring semimetal. The paper further claims that because the magnetism is soft and isotropic, rotating the magnetization continuously moves the Weyl nodes' positions and separation, so the topology can be controlled by the direction as well as the magnitude of the applied field. The experimental evidence—magneto-infrared shifts that scale linearly with magnetization, anisotropic magnetoresistance, Shubnikov-de Haas oscillations with a π-Berry phase, and an anomalous Hall conductivity consistent with the calculated Berry curvature—is presented as consistent confirmation of this exchange-driven evolution.","pith_inferences":["Beyond the paper: if the sequential polarization of the two Eu sublattices is confirmed by neutron diffraction, the 2/3-FiMa plateau becomes a rare example of a ferrimagnet whose intermediate state is defined by sublattice-selective polarization, which could be engineered in other Eu-Zintl compounds with inequivalent sites.","Beyond the paper: the linear M-scaling of optical transition energies could serve as a fast spectroscopic screening criterion to identify other low-carrier-density magnets with comparably giant exchange coupling, before expensive transport or photoemission studies.","Beyond the paper: the predicted rotation of Weyl node positions suggests that epitaxial strain or exchange bias from an adjacent magnetic layer could emulate field rotation, enabling non-volatile control of topology in devices without a rotating magnet.","Beyond the paper: the authors' note that transport near charge neutrality is still missing implies that gated nanowires, grown by the reported topotaxial method, could access the Weyl points directly and test the predicted (e2/2πh)Δk form of the intrinsic anomalous Hall effect."],"forward_implications":["Fields of about 1 T fully polarize the moments along any axis, so both the magnitude and the orientation of an applied field can switch the material among its insulating, intermediate, Weyl, and nodal-ring phases.","The Weyl phase has a single pair of nodes and no trivial bands at the Fermi level, offering a clean stage for testing Weyl physics such as the predicted relation between the anomalous Hall conductance and node separation.","Rotating the magnetization within the ab-plane moves the Weyl nodes along the kx-ky plane while preserving the Weyl semimetal, providing vectorial, in-situ tunability of Berry curvature and node separation.","Because the exchange splitting tracks magnetization, heating also reshapes the Fermi pocket, explaining the observed rise in the Shubnikov-de Haas frequency from 2 K to 20 K.","The L=0 spin-only moment, soft magnetism, and proximity of the magnetic ions to the conductive In-As framework are identified as the material-specific reasons the exchange coupling is both strong and easily steered."],"supporting_citations":[{"why":"provides the crystal structure and synthesis of Eu3In2As4, defining the two inequivalent Eu sublattices that the whole scenario builds on.","marker":"[30]"},{"why":"reports analogous consecutive magnetization steps on different Eu sites in Eu5In2As6, the prior example used to justify the sequential polarization scenario.","marker":"[31]"},{"why":"identifies hybrid-order topology and surface-dependent quantum geometry in Eu-based Zintl compounds, the basis for labeling the AFMa state an axion-insulator candidate.","marker":"[45]"},{"why":"demonstrates topotaxial growth of Eu3In2As4 nanowires with axion-insulator classification, underpinning the device-feasibility claims.","marker":"[46]"},{"why":"establishes EuCd2As2 as a magnetic semiconductor and is the comparative case for interpreting giant exchange-driven shifts rather than Weyl physics.","marker":"[53]"},{"why":"supplies the spin-only Heisenberg exchange Hamiltonian and the mean-field M/Msat scaling that connects measured transition shifts to band reconstruction.","marker":"[55]"},{"why":"gives the anomalous Hall conductivity formula for ideal type-I Weyl semimetals, used to interpret the measured AHE in terms of Weyl node separation.","marker":"[7]"},{"why":"provides the prior theoretical discovery that Eu3In2As4 hosts a single pair of Weyl points, which this paper extends with vectorial control and experimental evidence.","marker":"[94]"}],"fun_headline_variants":["Exchange giant steers a lone Weyl pair in Eu3In2As4","Field direction controls lone Weyl pair in Eu3In2As4","Field angle steers Weyl nodes via giant exchange","Exchange-driven topology: one Weyl pair, field-tunable","Magnetization rotation switches minimal Weyl semimetal"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The proposed 2/3-ferrimagnetic phase rests on the assumption that the two Eu sublattices polarize one after the other, an inference from magnetization derivatives that has not been confirmed by neutron diffraction or another magnetic-structure probe.","fun_headline_variants_meta":{"raw":{"variants":["Exchange giant steers a lone Weyl pair in Eu3In2As4","Field direction controls lone Weyl pair in Eu3In2As4","Field angle steers Weyl nodes via giant exchange","Exchange-driven topology: one Weyl pair, field-tunable","Magnetization rotation switches minimal Weyl semimetal"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000967,"raw_usage":{"total_tokens":4160,"prompt_tokens":1036,"completion_tokens":3124,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":652,"completion_tokens_details":{"reasoning_tokens":3034}},"tokens_in":652,"tokens_out":3124,"duration_ms":22529,"temperature":1.0,"reasoning_tokens":3034,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-10T21:35:20.291418+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Neutron diffraction on a single crystal at 1.8 K with field along the a-axis near the 2/3-Msat plateau would settle the intermediate phase: if the Eu1 sublattice is fully polarized while Eu2 retains antiferromagnetic order the sequential scenario holds, whereas simultaneous canting of both sublattices with no distinct plateau would invalidate it; separately, angle-resolved photoemission on the fully polarized state should reveal exactly one Weyl pair at the predicted kx-ky momenta, with any extra Fermi-surface crossings or trivial pockets refuting the minimal-Weyl claim.","supporting_citations":[{"cited_title":"Five new ternary indium -arsenides discovered. Syn- thesis and structural characterization of the Zintl phases Sr 3In2As4, Ba3In2As4, Eu3In2As4, Sr5In2As6 and Eu 5In2As6,","cited_arxiv_id":null,"evidence_quote":"provides the crystal structure and synthesis of Eu3In2As4, defining the two inequivalent Eu sublattices that the whole scenario builds on."},{"cited_title":"Hybrid-order topology in unconventional magnets of Eu- based Zintl compounds with surface-dependent quantum geometry,","cited_arxiv_id":null,"evidence_quote":"identifies hybrid-order topology and surface-dependent quantum geometry in Eu-based Zintl compounds, the basis for labeling the AFMa state an axion-insulator candidate."},{"cited_title":"Topotaxial mutual-exchange growth of magnetic Zintl Eu3In2As4 nanowires with axion insulator classification,","cited_arxiv_id":null,"evidence_quote":"demonstrates topotaxial growth of Eu3In2As4 nanowires with axion-insulator classification, underpinning the device-feasibility claims."},{"cited_title":"EuCd 2As2: A Magnetic Semiconductor,","cited_arxiv_id":null,"evidence_quote":"establishes EuCd2As2 as a magnetic semiconductor and is the comparative case for interpreting giant exchange-driven shifts rather than Weyl physics."},{"cited_title":"The discovery of three-dimensional Van Hove singularity,","cited_arxiv_id":null,"evidence_quote":"supplies the spin-only Heisenberg exchange Hamiltonian and the mean-field M/Msat scaling that connects measured transition shifts to band reconstruction."},{"cited_title":"Anomalous Hall Effect in Weyl Metals,","cited_arxiv_id":null,"evidence_quote":"gives the anomalous Hall conductivity formula for ideal type-I Weyl semimetals, used to interpret the measured AHE in terms of Weyl node separation."},{"cited_title":"Discovery of a Magnetic Topological Semimetal Eu$_3$In$_2$As$_4$ with a Single Pair of Weyl Points","cited_arxiv_id":"2403.07637","evidence_quote":"provides the prior theoretical discovery that Eu3In2As4 hosts a single pair of Weyl points, which this paper extends with vectorial control and experimental evidence."}],"review_version":1}