{"id":"0326cde6-f945-47b0-a765-ac405bd3f66f","arxiv_id":"2507.12946","paper_version":2,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":2,"one_line_summary":"Spin-polarized STM and DFT point to a magnetic triple-q (3Q3) ground state in a bismuthene-covered Mn monolayer on Ag(111), with field-switchable up and down domains.","lead":"Researchers made a single layer of bismuth on top of a manganese monolayer on silver and used spin-polarized scanning tunneling microscopy to see a noncollinear magnetic triple-q state. If the assignment holds, the structure is a new platform that combines a topological-insulator-like surface with an antiferromagnet for spintronic studies.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The claimed 3Q3 ground state is not established because the 2Q state, 2–3 meV/Mn lower without SOC in Fig. 5(a), is omitted from the SOC energy comparison, leaving the decisive competitor untested.","rationale":"I read the paper as making two coupled claims: the measured islands are bismuthene on p(1x1)-Mn/Ag(111), and the magnetic ground state of that structure is a 3Q3 texture whose SP-STM signatures are the observed checkerboard and stripe patterns. The reader's weakest_assumption focuses on the first claim, the structural assignment, which the paper itself admits cannot be distinguished by STM alone. I agree that this is a genuine concern. However, the more decisive internal problem is the missing SOC comparison with the 2Q state. The paper voluntarily reports in Fig. 5(a) that the 2Q state is 2–3 meV/Mn below the ideal 3Q state without SOC, and then all subsequent SOC calculations are restricted to 3Q and 1Q states. Since SOC shifts of order 5 meV/Mn are shown in the same figure, the no-SOC ordering cannot be assumed to survive. This is not a demand for an exotic calculation; it is the same noncollinear SOC machinery already used for the 3Q states, applied to the one competitor the authors themselves showed to be dangerous. I therefore see the missing 2Q SOC comparison as the single most load-bearing unaddressed point. The appropriate disposition remains conditional: the paper is publishable as a report of striking spin textures plus a plausible model, but the ground-state claim needs the additional calculation before full acceptance. My proposed check would settle it directly and uses only the methods already described in the manuscript.","tokens_in":15080,"tokens_out":4827,"duration_ms":54079,"concrete_test":"Using the same Fleur setup as in Fig. 5 (GGA-relaxed structure, LDA noncollinear calculations with self-consistent SOC), compute total energies of the 2Q state and of the distorted-3Q minimum from Fig. 5(a) with bismuthene shifted by +x, +y, and +xy as defined in Fig. 5(b), referenced to the 1Q_y state. If 2Q+xy or distorted-3Q+xy is lower than 3Q3+xy by more than about 1 meV/Mn, the abstract's ground-state claim is falsified; if 3Q3+xy remains lowest, the omission is benign and the central claim is supported.","verdict_should_be":"UNCHANGED","load_bearing_attack":"Figure 5(a) reports, without spin-orbit coupling, that along the continuous 2Q–3Q–1Q path the 2Q state and a distorted 3Q state are local minima 2–3 meV/Mn below the ideal 3Q state. The paper's central claim, stated in the abstract and conclusions, is that the 3Q3-like spin texture is the magnetic ground state for bismuthene-covered p(1x1)-Mn/Ag(111). The subsequent SOC analysis in Fig. 5(c,d) compares only 3Q_i shifted structures and collinear 1Q states; the 2Q and distorted-3Q competitors are never re-evaluated with SOC. This omission is consequential because the SOC shifts in Fig. 5(c) are up to about 5 meV/Mn, larger than the 2–3 meV/Mn no-SOC gap between 2Q and 3Q. Without the SOC energies of 2Q+xy and distorted-3Q+xy, one cannot know whether the 2Q state remains lower when SOC is included. Thus the DFT evidence, as presented, does not support the assertion that 3Q3 is the ground state, even under the authors' preferred bismuthene/Mn structural model. This is an internal gap in the presented calculation, not a disagreement with external consensus, and it is independent of the structural-model ambiguity noted by the reader.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"The manuscript reports the fabrication of a bismuthene-covered Mn monolayer on Ag(111), imaging of checkerboard and stripe magnetic patterns by spin-polarized scanning tunneling microscopy (SP-STM), and a combined experimental/theoretical interpretation in which the magnetic ground state is a noncoplanar 3Q3 spin texture. Field-dependent SP-STM shows exchange of checkerboard and stripe domains upon reversal of the out-of-plane field component, which the authors attribute to uniaxial magnetic anisotropy of the 3Q3 state induced by the bismuthene overlayer. DFT calculations are used to argue that the 3Q3 state is energetically favored and that its simulated SP-STM images reproduce the observed contrast.","tokens_in":15360,"tokens_out":5043,"duration_ms":63584,"significance":"If the central claim holds, the paper would provide a new experimental realization of a magnetic triple-q state in a bismuthene/Mn heterostructure, with the additional feature of uniaxial anisotropy and field-induced switching between 3Q3-up and 3Q3-down domains. This would be of interest for the growing field of noncollinear antiferromagnets and 2D topological-material/magnet interfaces. The experimental work is careful: the same scan area is imaged with two different Cr tip magnetizations, and the field-dependent measurements are supported by supplementary images. The DFT simulations provide an independent energy argument rather than a fit to the images, which is a strength. However, the theoretical ground-state claim is currently under-supported because a direct competitor of the 3Q state is not evaluated with spin-orbit coupling, and the structural model selection is not fully conclusive. The paper is therefore promising but not yet ready in its present form.","major_comments":[{"comment":"The no-SOC energy path in Fig. 5(a) shows that the 2Q state and a distorted 3Q state are minima 2–3 meV/Mn below the ideal 3Q state, as the text states explicitly. The SOC-included comparison in Fig. 5(c), however, contains only the 3Q_i shifted structures and collinear 1Q states; the 2Q and distorted-3Q candidates are never re-evaluated with SOC. Since the SOC shifts in Fig. 5(c) are up to about 5 meV/Mn, larger than the 2–3 meV/Mn no-SOC gap, the 2Q or distorted-3Q state could remain lower in total energy once SOC is included. As presented, the DFT evidence does not support the abstract and conclusions claim that the 3Q3-like spin texture is the ground state. The authors should either compute the SOC energies of the 2Q and distorted-3Q states or explicitly justify why these competitors can be excluded.","section":"Results and discussion, Fig. 5(a) and 5(c)"},{"comment":"The manuscript states that the two DFT-relaxed structural models, Mn honeycomb on BiAg3/Ag(111) and bismuthene on p(1x1)-Mn/Ag(111), 'appear nearly identical and can not be clearly distinguished on the basis of STM measurements and simulations.' The subsequent assignment of the measured islands to the bismuthene/p(1x1)-Mn model is then based on the magnetic ground state and on the SP-STM image match. This reasoning is not fully independent: the structural identification relies on the magnetic assignment, while the magnetic assignment is made within one of the two structures. The alternative Mn-honeycomb model is also computed to have an antiferromagnetic ground state whose simulated SP-STM contrast (Fig. 3(g,h)) includes a checkerboard pattern. To make the central claim load-bearing, the authors should provide a structural discrimination criterion that does not presuppose the 3Q ground state, or they should explicitly state that the sample structure remains ambiguous and correspondingly weaken the conclusions.","section":"Results and discussion, near Fig. 2(d) and Fig. 3"},{"comment":"The field-dependent SP-STM simulations reproduce the checkerboard and stripe patterns and their exchange only after introducing a canted tip magnetization with both in-plane and out-of-plane components (inset of Fig. 4(i,j)). This canted tip direction is an adjustable input rather than an independently measured quantity. Because the simulated contrast depends on the tip magnetization, the match in Fig. 4(k,l) is partly a consequence of this choice. The authors should quantify how sensitive the 3Q3 assignment is to the canting angle and to the relative spin/charge contributions, or provide an independent justification for the selected tip magnetization direction.","section":"Results and discussion, Fig. 4(i)-(l) and Methods"}],"minor_comments":[{"comment":"The substrate formula appears as '(p x root3)-Bi/Ag(111' with an unmatched parenthesis in both the abstract and the conclusions; this should be corrected to '(p x sqrt(3))-Bi/Ag(111)'.","section":"Abstract and Conclusions"},{"comment":"The caption contains duplicate panel labels '(i) ,(j)' for two different sets of simulated images; the second occurrence should refer to panels (k) and (l).","section":"Fig. 4 caption"},{"comment":"'stimulated SP-STM results' should be 'simulated SP-STM results'.","section":"Page 12, text near Fig. 4"},{"comment":"The notation '3Qi + y3, and Q i + xy' appears garbled; it should likely read '3Qi + y' and '3Qi + xy'.","section":"Page 13, text near Fig. 5(b)"},{"comment":"The relaxations are performed with PBE while the non-collinear energies are computed with LDA in the PBE-optimized geometry. Since the energy differences in Fig. 5(a) are only a few meV/Mn, the authors should comment on the sensitivity of the magnetic energy ordering to this functional choice.","section":"Methods, DFT calculations"}],"recommendation":"major_revision","confidential_remarks":"The paper is potentially publishable, but the central ground-state claim requires additional calculations: the 2Q and distorted-3Q states from Fig. 5(a) must be evaluated with SOC before the 3Q3 conclusion can be accepted. The structural ambiguity between the two DFT models also needs to be addressed more honestly, since the current text both admits the models are indistinguishable by STM and later uses the magnetic match to validate the chosen structure."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Two things you should know. First, this is the first magnetic 3Q state reported in a bismuthene/antiferromagnetic-monolayer interface. The SP-STM data show clean checkerboard and stripe contrasts that swap when the field flips, which is a strong experimental marker for a noncollinear texture with uniaxial anisotropy. Second, the paper's own DFT does not support its headline ground-state claim. In Fig. 5(a), without SOC, the 2Q state and a distorted 3Q state sit 2–3 meV/Mn below the ideal 3Q state. The SOC-included comparison (Fig. 3(a), Fig. 5(c,d)) only considers 3Q_i variants and collinear 1Q states; the 2Q and distorted-3Q competitors are never re-evaluated with SOC. Since SOC shifts in Fig. 5(c) reach about 5 meV/Mn, that gap is decisive: the claimed 3Q3 ground state is not established. The stress-test note is right.\n\nWhat the paper does well: the experiment is careful—same-area imaging with two Cr tip magnetizations is convincing; the DFT is independent, not fitted to images; the analysis into fourth- and sixth-order spin interactions is a sensible extension of the Mn/Re(0001) work; and the bismuthene-induced uniaxial anisotropy is a concrete, interesting mechanism for the domain switching.\n\nThe soft spots are two. (1) The missing SOC comparison above is the load-bearing one; it needs to be fixed before the abstract and conclusions can make the ground-state claim. (2) The structural model is unresolved: bismuthene on p(1x1)-Mn/Ag(111) and Mn honeycomb on BiAg3/Ag(111) look nearly identical in STM, and the paper acknowledges this. The 3Q assignment lives in one model, so the experimental structure is not strictly known. Additionally, the SP-STM simulations use a canted tip orientation; that is a free parameter, though it is not egregious.\n\nWho benefits: surface-magnetism and Xene-interface people. The paper deserves a serious referee; I would send it out, with the clear expectation of heavy revision—at minimum, a SOC-included energy comparison including 2Q and distorted 3Q, and ideally structural confirmation. If the 2Q state remains lower after SOC, the experimental observation might still be a 3Q-like state stabilized by the measurement condition or by the field, but the text will need to say so. Right now, the data are suggestive and the simulations are nice, but the central claim overreaches.","headline":"First 3Q state in a bismuthene/magnetic-monolayer interface, but the paper's own DFT omits the 2Q competitor from the SOC comparison, so the ground-state claim is not established as written.","tokens_in":16015,"tokens_out":3108,"would_cite":false,"duration_ms":32290,"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":"The bismuthene-covered manganese monolayer on Ag(111) has a noncoplanar 3Q3 magnetic ground state, and its uniaxial anisotropy makes the spin domains switch with external magnetic field.","keywords":["triple-q magnetic state","bismuthene","manganese monolayer","antiferromagnetic ordering","spin-polarized scanning tunneling microscopy","noncollinear spin texture","magnetic anisotropy","density functional theory"],"falsifier":"A structural determination of the same islands, for example a bias-dependent STM series or a local diffraction or spectroscopy probe that distinguishes the two relaxed atomic models, would settle the assignment; if the true structure is the Mn honeycomb on BiAg3, the 3Q claim does not transfer. Separately, a spin-polarized scan with the tip magnetization rotated in-plane could test whether the site-resolved spin pattern is tetrahedral 3Q3 rather than collinear c-AFM order.","tokens_in":1872,"feed_emoji":"🧲","tokens_out":1856,"duration_ms":82815,"temperature":0.7,"pith_summary":"The paper reports the fabrication of a single atomic layer of manganese on silver(111), capped by a honeycomb sheet of bismuth atoms called bismuthene. Using spin-polarized scanning tunneling microscopy, the authors resolve checkerboard and stripe magnetic patterns and argue that both patterns come from one magnetic ground state: a noncoplanar triple-q (3Q) spin texture, specifically the 3Q3 variant. Density-functional theory calculations show that the 3Q state is lowest in energy for the bismuthene-on-manganese structure and that its simulated SP-STM images reproduce the measured patterns. The bismuthene cap breaks the in-plane symmetry and gives the 3Q3 state a uniaxial magnetic anisotropy, which explains why reversing the magnetic field swaps the checkerboard and stripe domains. If correct, this is a controlled antiferromagnetic noncoplanar spin lattice underneath a two-dimensional topological material, making it a candidate platform for topological orbital moments and proximity effects.","feed_headline":"Bismuthene cap locks a manganese monolayer into triple-q magnetism","feed_subtitle":"SP-STM shows checkerboard and stripe spin patterns that swap when the magnetic field reverses.","key_machinery":"The central object is the 3Q spin texture: a noncoplanar arrangement formed by superposing three symmetry-equivalent spin spirals, giving four spins per (2x2) cell at tetrahedral angles close to 109.5 degrees. The argument is carried by three pieces of machinery: DFT total-energy comparisons that decompose the energy landscape into higher-order spin interactions (fourth-order terms stabilize the 3Q state while sixth-order terms distort it), spin-orbit-coupling calculations that scan 3Q orientations and registry shifts relative to the bismuthene lattice, and SP-STM image simulations that reproduce the measured checkerboard and stripe contrasts. The bismuthene registry selects a single in-plane anisotropy axis, which explains the absence of rotational domains and the field-driven switching between 3Q3-up and 3Q3-down.","core_discovery":"The central claim is that in the bismuthene-covered p(1x1)-Mn/Ag(111) system, the magnetic ground state is a 3Q3-like noncoplanar spin texture rather than a collinear antiferromagnet or a single-spiral state. The authors show that the 3Q state is energetically favored in DFT, that simulated SP-STM images of this state reproduce the checkerboard and stripe contrasts seen in experiment, and that the bismuthene overlayer induces a uniaxial magnetic anisotropy such that the 3Q3-up and 3Q3-down domains switch under an external out-of-plane magnetic field. They conclude that the measured islands are bismuthene on a p(1x1)-Mn monolayer with a (2x2) magnetic supercell, and that the measurements validate the energetically preferred structure while supporting the magnetic 3Q interpretation.","pith_inferences":["Beyond the paper: the structural assignment is the load-bearing step, since the two relaxed models look nearly identical in STM topography and only the bismuthene-on-Mn model yields the 3Q ground state; a direct structural probe of the islands would settle whether the 3Q interpretation transfers to the measured sample.","Beyond the paper: a spin-resolved measurement that isolates the in-plane spin components at each sublattice site could test the tetrahedral 3Q3 spin arrangement against the collinear c-AFM alternative without relying on image matching.","Beyond the paper: sweeping the magnetic field through intermediate values may reveal domain walls or partial spin reorientation, providing additional evidence for the uniaxial anisotropy mechanism.","Beyond the paper: similar growth recipes on other group-V Xene overlayers could produce related noncoplanar antiferromagnetic spin textures and expand the family of two-dimensional magnetic/topological interfaces."],"forward_implications":["The bismuthene/Mn/Ag(111) interface becomes a concrete two-dimensional antiferromagnet with noncoplanar 3Q order that can be imaged in real space.","Checkerboard and stripe SP-STM patterns can serve as fingerprints distinguishing a 3Q spin texture from a collinear c-AFM order in this system.","Reversing an external out-of-plane magnetic field swaps the 3Q3-up and 3Q3-down domains, giving a deterministic way to manipulate the noncoplanar magnetic state.","The uniaxial anisotropy means rotational domains are absent, so field-driven switching happens along a single magnetic axis.","Because noncoplanar 3Q configurations can carry topological orbital moments, the system is a candidate for emergent topological Hall effects without spin-orbit interaction."],"supporting_citations":[{"why":"Predicted the three-dimensional noncollinear 3Q magnetic state for a monolayer Mn on Cu(111), providing the theoretical model this paper applies to Mn/Ag(111).","marker":"[13]"},{"why":"Shows that a distorted 3Q state can be stabilized by higher-order topological-chiral magnetic interactions, supplying the energy-decomposition framework used in the DFT analysis.","marker":"[15]"},{"why":"Reported the experimental discovery of single- and triple-q states in Mn/Re(0001), including the rotations between 3Q_i states used here to identify the 3Q3 texture.","marker":"[19]"},{"why":"Connects noncoplanar 3Q spin configurations to topological orbital moments and emergent Hall effects, which motivates why the 3Q state is of interest.","marker":"[22]"},{"why":"Establishes the pseudomorphic p(1x1) Mn monolayer on Ag(111) that is the substrate layer in the bismuthene-on-Mn structural model.","marker":"[59]"},{"why":"Characterizes the starting (p x sqrt3)-Bi/Ag(111) surface from which the bismuthene-covered structure forms.","marker":"[60]"},{"why":"Provides the density-functional theory implementation used for structure relaxations and noncollinear spin-orbit calculations.","marker":"[67]"}],"fun_headline_variants":["Triple-q magnetism emerges in bismuthene-capped Mn monolayer","SP-STM resolves triple-q state in Mn monolayer with bismuthene","Field-switchable triple-q order in Mn monolayer/bismuthene","Bismuthene induces 3Q ground state in Mn monolayer","Noncoplanar triple-q magnetism in Mn under bismuthene"],"cache_read_input_tokens":17920,"weakest_assumption_plain":"The measured islands really are bismuthene on a p(1x1)-Mn monolayer rather than the nearly identical Mn honeycomb lattice on BiAg3; the two relaxed models cannot be distinguished by STM topography, and only the bismuthene-on-Mn model gives the 3Q ground state and matching SP-STM contrast.","fun_headline_variants_meta":{"raw":{"variants":["Triple-q magnetism emerges in bismuthene-capped Mn monolayer","SP-STM resolves triple-q state in Mn monolayer with bismuthene","Field-switchable triple-q order in Mn monolayer/bismuthene","Bismuthene induces 3Q ground state in Mn monolayer","Noncoplanar triple-q magnetism in Mn under bismuthene"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000313,"raw_usage":{"total_tokens":1740,"prompt_tokens":868,"completion_tokens":872,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":484,"completion_tokens_details":{"reasoning_tokens":776}},"tokens_in":484,"tokens_out":872,"duration_ms":8657,"temperature":1.0,"reasoning_tokens":776,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-06T16:34:28.606310+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"A structural determination of the same islands, for example a bias-dependent STM series or a local diffraction or spectroscopy probe that distinguishes the two relaxed atomic models, would settle the assignment; if the true structure is the Mn honeycomb on BiAg3, the 3Q claim does not transfer. Separately, a spin-polarized scan with the tip magnetization rotated in-plane could test whether the site-resolved spin pattern is tetrahedral 3Q3 rather than collinear c-AFM order.","supporting_citations":[{"cited_title":"et al.Experimental Observation of the Quantum Anomalous Hall Effect in a Magnetic Topological Insulator","cited_arxiv_id":null,"evidence_quote":"Shows that a distorted 3Q state can be stabilized by higher-order topological-chiral magnetic interactions, supplying the energy-decomposition framework used in the DFT analysis."}],"review_version":1}