{"id":"8117647d-d50a-4e6e-aaa6-e1afa0b032a7","arxiv_id":"2502.08117","paper_version":3,"verdict":"ACCEPT","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"low","formal_verification":"none","parameter_count":2,"one_line_summary":"Single-crystalline CrSb(1-10) films with -1.0% strain were grown on GaAs(001) using FeSb/AlAs buffers and show two-carrier semimetallic transport without a spontaneous anomalous Hall effect.","lead":"Researchers grew a thin film of CrSb, a magnetic material whose electronic spins split by direction, on a standard GaAs semiconductor chip by inserting two thin buffer layers. The film is strained and conducts like a semimetal, a step toward putting this new class of magnets onto ordinary semiconductor devices.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The 1 ML FeSb template's chemical inertness is unverified; without element-resolved interface data, the film may be Fe-doped CrSb, which would alter the transport and symmetry claims.","rationale":"The reader's weakest assumption is exactly the one I identify: the 1 ML FeSb layer is assumed to be an inert template, but no composition measurement rules out Fe incorporation into CrSb. This is load-bearing because the title, abstract, and conclusion call the film 'CrSb' and use its transport properties to infer altermagnetic behavior. If Fe diffuses even at the few-percent level, the measured carrier densities, mobilities, and the calculated anomalous Hall conductivity would correspond to a doped or alloyed system, not intrinsic CrSb. I considered the missing anomalous Hall effect as an alternative concern, but the absence of a net AHE can be explained by multi-domain Néel order and does not by itself threaten the structural epitaxial-growth claim. I also weighed the strain analysis, which is internally consistent with the RSM data. The composition gap is the most concrete and testable weakness, and the supplementary evidence that Fe becomes reactive at 550 °C makes it plausible, not merely speculative. The appropriate response is to condition acceptance on an element-resolved composition check; if the check shows negligible Fe, the paper's claims stand.","tokens_in":15735,"tokens_out":5675,"duration_ms":85904,"concrete_test":"Perform a sub-nm-resolution STEM-EDX/EELS line scan across CrSb/FeSb/AlAs (and, if possible, atom-probe tomography) on the as-grown and 400 °C-annealed samples. Quantify Fe concentration in the CrSb layer with a detection limit below about 1 at%. If Fe is below this threshold throughout the 30 nm film, the claim stands; if Fe is present, repeat the band-structure and AHC calculations for Cr1-xFexSb and reassess the transport interpretation.","verdict_should_be":"CONDITIONAL","load_bearing_attack":"The central claim is that a single-crystalline stoichiometric CrSb (1-10) film grows on GaAs(001) via a 1 ML FeSb template. This requires the template to act only as a structural seed. The paper provides no EDX, XPS, SIMS, or EELS composition profile across CrSb/FeSb/AlAs. XRD and STEM establish NiAs-type crystallinity and lattice constants, but a few percent of Fe substituting on Cr sites would be hard to detect by XRD and would shift the carrier balance; it could also change the magnetic anisotropy and the AHC that the paper calculates. The supplementary 550 °C anneal (Fig. S6) actually forms an Fe1-xCrxAs secondary phase, showing Fe is mobile at accessible temperatures; the 400 °C anneal used for the main sample could in principle intermix below the XRD detection limit. Thus the identification of the transport data as those of intrinsic CrSb is an assumption, not a demonstrated result.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper reports the molecular-beam-epitaxial growth of a nominally single-crystalline CrSb (1-10) thin film on a GaAs (001) substrate using a 5 nm AlAs buffer and a 1 ML FeSb template layer. The authors establish the epitaxial relationship CrSb[110] || GaAs[110] and CrSb[001] || GaAs[1-10], quantify the in-plane strain as approximately -1.0%, and characterize the film by XRD, phi-scans, RSM, STEM, SQUID magnetometry, and magnetotransport. DFT band-structure and anomalous Hall conductivity calculations are performed for the measured lattice constants. The transport data are analyzed with a two-carrier model, and the authors conclude that the Hall response is explained by coexisting electrons and holes rather than by a spontaneous anomalous Hall effect, with no hysteresis observed.","tokens_in":15920,"tokens_out":4578,"duration_ms":43058,"significance":"If the growth claim is substantiated, the paper provides a useful integration route for the altermagnet CrSb on a technologically standard III-V (001) platform, with a defined epitaxial orientation and a controllable compressive strain of about -1.0%. The structural characterization is thorough and internally consistent: XRD shows only CrSb (hh0) peaks, the STEM image shows a coherent NiAs-type lattice, the RSM values are consistent with a strained hexagonal cell, and the phi-scan supports single-crystalline in-plane alignment. The transport analysis is unusually candid about its assumptions: anisotropic conductivity and Onsager symmetry are stated explicitly, and the two-carrier fit is presented with error bars. The DFT calculation is also transparent in using measured lattice constants and a Hubbard U borrowed from previous work, rather than claiming parameter-free prediction. The main value of the paper is the growth method itself and the demonstration that Hall transport in this film is dominated by multi-carrier semimetallic behavior, which is a useful baseline for future strain-engineering studies.","major_comments":[{"comment":"The central growth claim requires that the 1 ML FeSb layer acts as an inert structural template, but no element-resolved interface or composition profile (EELS, EDX, XPS, or SIMS) is provided to rule out Fe incorporation into the CrSb layer. The authors' own Supplementary Fig. S6 shows that at a 550 C anneal Fe becomes mobile enough to form a Fe1-xCrxAs secondary phase, so Fe diffusion at the 400 C anneal used for the main sample is a real risk even if it is below the XRD detection limit. A few percent of Fe on Cr sites would change the carrier balance and could affect the magnetic anisotropy and the altermagnetic interpretation of the transport data. I request either a direct interface-composition measurement or, failing that, an explicit statement that the transport properties are reported for a film that may contain interfacial Fe interdiffusion, with a discussion of how this could affect the conclusions.","section":"Section III.A, Fig. 1(d); Supplementary Fig. S6"},{"comment":"The two-carrier fit is the basis for the central negative result that no spontaneous anomalous Hall effect is observed, but the fit quality is not uniform. At 300 K there is a visible deviation in sigma_xx at low fields, and the authors note that the 300 K error bars are too large to be plotted. This makes the extracted 300 K carrier densities and mobilities unreliable, and it weakens the quantitative statement about the temperature dependence of the carrier system. I ask the authors to show the fit residuals, state explicitly which temperature points pass the goodness-of-fit criterion, and discuss whether a three-carrier or field-dependent mobility model could change the inferred absence of an AHE component at the level claimed.","section":"Section III.D, Fig. 5"},{"comment":"The calculation of the anomalous Hall conductivity uses U = 0.25 eV for Cr 3d, with the justification that this value reproduced lattice constants and magnetic moments in previous work. Since the paper uses the calculated AHC value (~20 S/cm) to argue that a spontaneous AHE should have been detectable in this sample, the sensitivity of this conclusion to the choice of U and to the use of scalar-relativistic (rather than fully relativistic) calculations should be stated. A test with a modest range of U values, or at least a statement of the known uncertainty in AHC from this approximation, would make the 'should be detectable' argument proportionate.","section":"Section II.B, Fig. 2(d)"}],"minor_comments":[{"comment":"The text says 'a 1-ML-thick AlAs and 1-ML-thick FeSb layers are necessary,' but the sample structure and Methods describe a 5-nm AlAs layer, not a 1-ML AlAs layer. This is inconsistent and should be corrected.","section":"Section III.A, Methods"},{"comment":"The magnetization value is given as '4.3×102 & μB/Cr atom,' which appears to be a typographical corruption of 4.3×10^-2 μB/Cr atom. Please verify the exponent and the notation throughout the manuscript, as the same symbol '&' appears in several other places.","section":"Section III.C, Fig. 3"},{"comment":"There is a typo in 'we expect that stain induces the DMI-like field'; 'stain' should be 'strain.'","section":"Section III.D, text after Eq. (3)"},{"comment":"Reference [55] is cited as the source of the Hubbard U value, but [55] is a 1952 neutron-diffraction paper on the magnetic structure of CrSb. The citation does not appear to support the U choice. Please re-check the reference list and insert the actual source of U = 0.25 eV.","section":"Section II.B, references"},{"comment":"The quantities d110 and d1-10 are used in Eq. (1) but are not defined until later in the text. Please define them at first use and state explicitly how they are obtained from the RSM measurement.","section":"Eq. (1)"}],"recommendation":"major_revision","confidential_remarks":"The paper is likely of interest to the cond-mat.mtrl-sci readership, and the growth result appears reproducible in structure and strain. The main issue is evidentiary: the role of the FeSb monolayer as a chemically passive template is asserted rather than demonstrated, and this assumption is load-bearing for the transport and altermagnetic interpretation. I recommend asking for interface composition data or a clearly worded limitation. I do not see grounds for outright rejection; the structural story is strong and the transport analysis is more transparent than is typical."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"CrSb on GaAs(001) is a useful, credible growth result, and the paper is worth refereeing. The genuinely new piece is the 1 ML FeSb/AlAs buffer that stabilizes single-crystalline CrSb(1-10) on GaAs(001), with CrSb[110] || GaAs[110] and about -1.0% compressive strain. The structural evidence hangs together: XRD shows only (hh0) peaks, the phi-scan and RSM support the single-crystalline orientation and strain, and the STEM image shows an abrupt interface. The supplementary sample without FeSb is a good control and shows why the template matters. The transport analysis is careful and transparent; the two-carrier fit is standard, and the authors explicitly state the isotropy and Onsager assumptions and note that a spontaneous AHE is not observed even though their DFT calculation puts the intrinsic AHC around 20 S/cm. I don't read the missing AHE as a flaw; they discuss possible reasons and leave strain engineering as future work.\n\nThe real soft spot is the chemical integrity of the FeSb template. There is no element-resolved profile across the CrSb/FeSb/AlAs interface, so we only have XRD and STEM evidence that the film is stoichiometric CrSb. The authors themselves show that annealing at 550 C produces Fe1-xCrxAs, which proves Fe is mobile at accessible temperatures. It is possible that the 400 C anneal used for the main sample causes some intermixing below the XRD detection limit. That would not overturn the structural claim, but it would mean the carrier densities and mobilities might not be intrinsic CrSb properties. This is the main thing a referee should ask for: EDX/EELS or SIMS across the interface.\n\nThe magnetization and transport interpretations are otherwise measured. The tiny ferromagnetic component is discussed with appropriate caution, and the possible surface origin is acknowledged. The citations cover the relevant CrSb and MnAs literature; nothing looks missing.\n\nWho should read this: people growing altermagnet films and anyone wanting a III-V integration route for CrSb. It is a subfield advance, not a breakthrough. I would send it to peer review and ask for interface composition data rather than desk-reject it.","headline":"Worth refereeing: a credible CrSb-on-GaAs(001) growth route with one unproven interface — ask for composition data before trusting the transport as intrinsic.","tokens_in":16489,"tokens_out":4498,"would_cite":true,"duration_ms":43939,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"A one-monolayer FeSb template makes single-crystalline altermagnet CrSb grow on GaAs(001), with -1.0 percent compressive strain.","keywords":["altermagnet","CrSb","molecular beam epitaxy","GaAs(001)","heteroepitaxy","epitaxial strain","anomalous Hall effect","magnetotransport"],"falsifier":"An atomically resolved composition profile across the CrSb/FeSb/AlAs stack (for example an EELS or EDS line scan) would settle it: Fe present inside the 30-nm CrSb beyond the intended monolayer, or CrSb (1-11) and (1-12) XRD peaks reappearing in a repeat growth, would falsify the claim that the FeSb template alone produces single-crystalline, stoichiometric, strain-engineered CrSb.","tokens_in":15525,"feed_emoji":"🧲","tokens_out":6344,"duration_ms":53783,"temperature":0.7,"pith_summary":"This paper reports that a single-crystalline film of the altermagnet CrSb can be grown on a GaAs (001) semiconductor substrate, a combination previously unavailable because the two crystal systems are structurally dissimilar. The key is a one-monolayer FeSb template on an AlAs buffer that stabilizes the (1-10) growth plane, yielding the intended in-plane relationship CrSb[110] \\parallel GaAs[110], CrSb[001] \\parallel GaAs[1-10], with about -1.0% compressive strain. That strain matters because unstrained CrSb has mirror and glide symmetries that forbid the anomalous Hall effect and weak ferromagnetism, so strain is a lever for N\\'eel-vector control. The authors confirm single crystallinity by XRD and STEM, and show magnetotransport consistent with a semimetallic two-carrier system, although no spontaneous anomalous Hall signal is observed. If the growth recipe holds, it opens III-V semiconductor platforms for strain-engineered altermagnet devices.","feed_headline":"One FeSb monolayer grows altermagnet CrSb on GaAs(001)","feed_subtitle":"A 30-nm single-crystal film forms on a standard III-V substrate with -1.0% strain, a platform for strain-tuned spintronics.","key_machinery":"The mechanism that carries the growth is the 1-ML FeSb template: FeSb has the same NiAs-type crystal structure as CrSb and nearly the same lattice constants, so it seeds the (1-10) plane on AlAs/GaAs(001) and suppresses competing (1-11) and (1-12) orientations. The interface then settles into a 7-to-5 registry, with seven GaAs/AlAs (1-10) spacings matching five CrSb (001) spacings, producing an atomically abrupt interface and the measured -1.0% strain. On the physics side, the load-bearing symmetry argument is that this strain removes four of the mirror and glide operations in CrSb, allowing a T-odd axial vector, namely the anomalous Hall vector and a possible weak ferromagnetic moment, along CrSb[1-10]; the first-principles Wannier calculation supplies the magnitude, about 20 S/cm, that transport did not detect.","core_discovery":"The central claim is that inserting a 1-ML FeSb (1-10) layer between a 5-nm AlAs buffer and CrSb turns an otherwise polycrystalline or misoriented growth into a single-crystalline CrSb (1-10) film on GaAs(001), with CrSb[110] parallel to GaAs[110] and CrSb[001] parallel to GaAs[1-10]. The film is compressively strained by $\\varepsilon = -1.0\\%$ along CrSb[110] (with $\\varepsilon$ defined relative to the regular hexagonal plane), which partially breaks the glide and magnetic-mirror symmetries that forbid T-odd axial vectors in bulk CrSb. First-principles band-structure and Berry-curvature calculations using the measured lattice constants give a sizable anomalous Hall conductivity around 20 S/cm, but the measured Hall resistivity contains no hysteretic anomalous component; instead, a two-carrier fit describes it with electron and hole carriers and indicates a semimetal with carrier densities in the $10^{20}\\,\\mathrm{cm}^{-3}$ range and mobilities around $10^4\\,\\mathrm{cm}^2/\\mathrm{V\\,s}$. The authors interpret the missing AHE as likely meaning the N\\'eel vector has not been reversed in this strain state, not that the altermagnetic order is absent.","pith_inferences":["Editorial extension: if the FeSb monolayer truly remains confined to the interface, the recipe should transfer to other NiAs-type altermagnets and to InGaAs or InAlAs buffers, where buffer composition tunes strain continuously without changing the template.","Editorial extension: the absence of a spontaneous AHE could also arise from N\\'eel-domain averaging rather than insufficient strain; sweeping the magnetic field along the allowed $h$ direction while monitoring $\\rho_{yx}$ would separate these possibilities.","Editorial extension: adding an anomalous Hall term to the two-carrier fit, rather than subtracting an ordinary-Hall background, would give a direct upper bound on any small AHE in this strain state.","Editorial extension: if Fe diffuses into the CrSb layer, the film is really Cr$_{1-x}$Fe$_x$Sb; comparing the measured carrier densities and mobilities against first-principles results for the alloy would test the stoichiometry assumption."],"forward_implications":["CrSb can be integrated on the widely used GaAs(001) platform without a lattice-matched substrate, because the FeSb/AlAs buffer controls the orientation rather than the lattice matching.","The measured -1.0% compressive strain breaks the symmetry that forbids the anomalous Hall response in bulk CrSb, making this film recipe a platform for testing strain-induced N\\'eel-vector reversal.","The two-carrier transport analysis says the film is a semimetal with coexisting electrons and holes, with mobility up to about $1.8 \\times 10^4\\,\\mathrm{cm}^2/\\mathrm{V\\,s}$, consistent with bulk CrSb behavior.","Annealing at 550\\,°C lowers the strain to -0.7% and produces a Fe$_{1-x}$Cr$_x$As secondary phase, indicating that there is a growth-temperature window for keeping the intended single-phase structure.","Because III-V buffer composition can be graded, the same growth route can provide continuous strain control beyond the -1.0% demonstrated here."],"supporting_citations":[{"why":"Supplies the altermagnetic band-splitting signature of CrSb thin films and a prior (1-10)-on-GaAs(110) growth that this work moves to GaAs(001).","marker":"[29]"},{"why":"Reports strain-induced anomalous Hall sign reversal in CrSb with +1.0% strain, the key comparison point for the -1.0% strain studied here.","marker":"[37]"},{"why":"Demonstrates that the first monolayers decide the orientation of NiAs-type MnAs on GaAs(001), the template idea adapted in this paper.","marker":"[51]"},{"why":"Extends the MnAs/III-V hybrid growth principle that motivates the FeSb/AlAs buffer design.","marker":"[52]"},{"why":"Gives the bulk lattice constants of CrSb used to quantify the -1.0% strain.","marker":"[33]"},{"why":"Establishes the high N\\'eel temperature and A-type antiferromagnetic spin configuration of CrSb.","marker":"[34]"},{"why":"Provides FeSb lattice constants and structure, justifying why one monolayer of FeSb seeds the CrSb (1-10) plane.","marker":"[61]"},{"why":"Predicts that axial strain alone cannot switch the CrSb easy axis, motivating the symmetry-breaking route used here.","marker":"[41]"}],"fun_headline_variants":["FeSb monolayer enables single-crystal CrSb on GaAs","CrSb on GaAs via FeSb: single-crystal, -1.0% strain","Altermagnet CrSb film on GaAs: no AHE, two-carrier transport","Single-layer FeSb seeds epitaxial CrSb on GaAs(001)"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The 1-ML FeSb layer must act only as a structural template, staying at the interface; if Fe diffuses into CrSb during growth or annealing, the film becomes a Fe-doped alloy and the reported strain, symmetry, and transport interpretations would need revision.","fun_headline_variants_meta":{"raw":{"variants":["FeSb monolayer enables single-crystal CrSb on GaAs","CrSb on GaAs via FeSb: single-crystal, -1.0% strain","Altermagnet CrSb film on GaAs: no AHE, two-carrier transport","Single-layer FeSb seeds epitaxial CrSb on GaAs(001)"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.001121,"raw_usage":{"total_tokens":4804,"prompt_tokens":1222,"completion_tokens":3582,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":838,"completion_tokens_details":{"reasoning_tokens":3496}},"tokens_in":838,"tokens_out":3582,"duration_ms":23089,"temperature":1.0,"reasoning_tokens":3496,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-08T10:22:21.972928+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"An atomically resolved composition profile across the CrSb/FeSb/AlAs stack (for example an EELS or EDS line scan) would settle it: Fe present inside the 30-nm CrSb beyond the intended monolayer, or CrSb (1-11) and (1-12) XRD peaks reappearing in a repeat growth, would falsify the claim that the FeSb template alone produces single-crystalline, stoichiometric, strain-engineered CrSb.","supporting_citations":[],"review_version":1}