{"id":"3792bb17-cc27-44df-adb2-576f38cd3fbc","arxiv_id":"2607.06792","paper_version":1,"verdict":"ACCEPT","confidence":"HIGH","novelty_score":7.0,"correctness_risk":"low","formal_verification":"none","parameter_count":0,"one_line_summary":"Zero-field chiral phonons with g-wave phonon angular momentum emerge in altermagnetic CrSb from relativistic magnon-phonon hybridization, enabling anomalous spin and PAM Nernst effects.","lead":"Relativistic magnon-phonon coupling in the altermagnet CrSb produces chiral phonons at zero magnetic field, imprinting g-wave symmetry on phonon angular momentum. This positions bulk altermagnets as candidates for field-free spin caloritronics and chiral phononics.","discovery_kind":"new_application","skeptic_critique":{"model":"grok-4.5","headline":"No significant objection identified","rationale":"The paper’s strongest claim rests on three pillars that hold: (i) PT is broken by the altermagnetic order, so neither PAM nor Berry curvature is forced to vanish; (ii) the first-principles SLC vertices open avoided crossings of order 1 meV, transferring the g-wave magnon texture onto the phonon angular momentum (Figs. 1–2 and Table I); (iii) the resulting finite Berry curvatures produce symmetry-allowed anomalous Nernst coefficients (Fig. 4). The linear-order truncation flagged by the reader is the usual starting point for magnon-polaron calculations and is not a correctness risk for the existence claim. Experimental confirmation and open data would strengthen the work but are not required for an ACCEPT verdict on a first-principles prediction. Consequently the reader’s ACCEPT / high-confidence assessment stands without adjustment.","tokens_in":12789,"tokens_out":502,"duration_ms":6239,"concrete_test":"Recompute the hybridized spectrum and PAM helicity of Fig. 1 after artificially scaling the entire SLC tensor J^{αβμ} by factors 0.5 and 2.0; if the g-wave nodal structure and the sign-reversal of helicity between Γ–L and Γ–L' survive both scalings, the qualitative claim is robust to the linear-order truncation.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim—that relativistic SLC hybridizes altermagnetic magnons with phonons in CrSb, imprinting a g-wave PAM texture and finite Berry curvatures that drive zero-field anomalous spin/PAM Nernst responses—is internally consistent and well-supported by the first-principles pipeline (KKR force-theorem SLC tensors, Holstein-Primakoff mapping, Colpa diagonalization of Eq. 2, and symmetry analysis under 6'/m'mm'). The reader’s weakest assumption (linear-order truncation of the SLC tensor) is a standard approximation whose neglect of higher-order magnetoelastic and anharmonic terms does not undermine the zero-field existence proof or the symmetry-enforced g-wave pattern; those higher-order terms would only renormalize gap sizes and transport magnitudes, not reverse the PT-breaking selection rules that permit finite PAM and Berry curvature. No load-bearing inconsistency or hidden assumption that would falsify the claim was found.","agreement_with_reader":"agree"},"referee_report":{"model":"grok-4.5","summary":"The manuscript argues that PT-breaking altermagnets host zero-field chiral phonons because relativistic spin-lattice coupling hybridizes altermagnetic magnons with phonons. Using first-principles IFCs (VASP/phonopy), relativistic KKR exchange and SLC tensors, Holstein-Primakoff mapping, and Colpa diagonalization of the coupled Hamiltonian (Eq. 2), the authors compute magnon-polarons across the full BZ of CrSb. They show that the hybridized bands acquire a finite phonon angular momentum whose momentum-space texture is forced by the magnetic point group 6'/m'mm' into a g-wave pattern with four nodal planes, and that the associated Berry curvatures produce zero-field anomalous spin and PAM Nernst responses (Eqs. 4–5, Fig. 4). Total equilibrium PAM remains compensated until an external field is applied (Fig. 3).","tokens_in":12997,"tokens_out":1030,"duration_ms":20350,"significance":"If correct, the work supplies a symmetry-allowed route to chiral lattice dynamics and anomalous transverse spin/PAM transport in compensated magnets without net magnetization, applied field, or structural chirality. That is a concrete materials platform for zero-field spin caloritronics and chiral phononics. Strengths include a parameter-free first-principles pipeline (force-theorem SLC tensors, full-BZ Colpa diagonalization), an explicit group-theoretic derivation of the g-wave PAM texture under 6'/m'mm' (Table I), and clear separation of the nonrelativistic PAM Hall background from the SLC-activated spin Nernst signal. The distinction from minimal 2D toy models and from electron-phonon mechanisms is stated carefully.","major_comments":[{"comment":"The central existence claim rests on the linear-order SLC tensor J^{αβμ} (Eq. 1, final term) together with the Holstein-Primakoff + Colpa treatment of Eq. 2. While this is standard, the manuscript never quantifies the size of neglected higher-order magnetoelastic or anharmonic corrections relative to the reported 1.1 meV hybridization gaps. A short estimate (or a statement that such terms only renormalize gap sizes without restoring PT) would make the zero-field selection-rule argument more robust.","section":null},{"comment":"Experimental accessibility is asserted in the conclusion but not demonstrated. The hybridization gaps open near ~11 meV and the spin Nernst coefficient is two orders of magnitude smaller than the PAM Nernst signal. A brief comparison of these energy and transport scales with existing inelastic neutron, Raman, or thermal-transport resolution on CrSb (or related altermagnets) is needed to substantiate the claim that bulk altermagnets are immediately useful for zero-field spin caloritronics.","section":null}],"minor_comments":[{"comment":"Supplemental Material is cited as “available at tbc” (Ref. [44]). The SM must be supplied and the citation completed before acceptance.","section":null},{"comment":"Figure 1 caption and main text refer to “phonon helicity” while the color scale is defined only later; a one-sentence definition in the caption would help.","section":null},{"comment":"Table I lists generators of 6'/m'mm' but does not explicitly state how the PAM Berry curvature Ω^{L_z}_{xy} transforms under C'_{6z}; adding that row (or a short note) would complete the symmetry table.","section":null},{"comment":"The statement that conventional macroscopic magnetoelastic theories “inherently lack” the dynamic DMI-like term (paragraph after Eq. 2) is strong; a brief citation to the standard Kittel or Callen–Callen forms would clarify the contrast.","section":null},{"comment":"In Fig. 4(c) the nonrelativistic PAM Nernst background is shown as dashed curves; stating the numerical ratio of SLC correction to background at 300 K in the text (currently only “~20 %”) would make the figure self-contained.","section":null},{"comment":"Typographical: “altermagneticg-wave” (abstract) and “PT-breaking” spacing inconsistencies appear in a few places; a final proof-read is warranted.","section":null}],"recommendation":"minor_revision","confidential_remarks":"The concurrent arXiv preprint on d-wave PAM textures in 2D altermagnets (Bendin et al., cited as [56]) is properly distinguished, but the editor may wish to confirm that the bulk, first-principles CrSb calculation is not overlapping with any simultaneous submission by the same group. The work is solid theory and fits a high-impact condensed-matter journal; I see no reason for rejection."},"author_rebuttal":null,"desk_editor":{"model":"grok-4.5","letter":"The real advance here is straightforward: they show that bulk CrSb, a compensated altermagnet, can host chiral phonons and finite Berry-curvature-driven spin/PAM Nernst responses at zero field. Relativistic spin-lattice coupling hybridizes the altermagnetic magnons with phonons and imprints the g-wave PAM texture required by the 6'/m'mm' point group. That is new relative to the ferromagnet and field-polarized cases (including their own earlier work) and relative to the 2-D toy models that needed broken mirror symmetry.\n\nThey do the calculation properly. IFCs from VASP+phonopy, fully relativistic KKR force-theorem exchange and SLC tensors, Holstein-Primakoff mapping, and Colpa diagonalization of the hybridized Hamiltonian across the full zone. The avoided crossings, the helicity sign reversal between Γ–L and Γ–L', the nodal planes of Lz, and the form of the Nernst tensors all match the magnetic point-group constraints. The linear-order truncation of the SLC is the usual approximation; higher-order magnetoelastic or anharmonic terms would renormalize gaps and magnitudes but cannot restore PT and erase the selection rules that allow finite PAM and Berry curvature. No free parameters, no circular fitting.\n\nSoft spots are the expected ones for a pure theory paper: no experimental spectra or transport numbers, data available only on request, and the PAM Nernst already has a non-relativistic background that the hybridization only modulates at higher T. The zero-field spin Nernst is cleaner. None of this undercuts the existence proof or the symmetry result.\n\nThis is for people working on altermagnets, spin caloritronics, or chiral phonons who want a concrete bulk materials route that does not require net magnetization or external field. It deserves a serious referee. I would engage with it.","headline":"Clean first-principles demonstration that PT-breaking altermagnets host zero-field g-wave chiral phonons and anomalous Nernst responses via relativistic magnon-phonon hybridization; methods and symmetry analysis hold up.","tokens_in":13600,"tokens_out":477,"would_cite":true,"duration_ms":5199,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"grok-4.5","headline":"Relativistic magnon-phonon coupling produces zero-field chiral phonons with g-wave angular momentum in altermagnets such as CrSb.","keywords":["altermagnets","chiral phonons","magnon-phonon coupling","phonon angular momentum","spin-lattice coupling","Nernst effect","Berry curvature","CrSb"],"falsifier":"Momentum-resolved measurements (Raman, X-ray, or inelastic neutron scattering) of phonon helicity in zero-field CrSb that fail to show the predicted g-wave sign reversals between the Gamma-L and Gamma-L-prime paths, or the absence of the calculated anomalous Nernst coefficients above ~100 K, would refute the central claim.","tokens_in":13714,"feed_emoji":"🌀","tokens_out":914,"duration_ms":23527,"temperature":0.7,"pith_summary":"Conventional antiferromagnets cannot host chiral phonons at zero field because PT symmetry forces phonon angular momentum and Berry curvature to vanish everywhere. Altermagnets break PT while remaining fully compensated, so their magnons already carry an unconventional spin-split pattern. This paper shows that relativistic spin-lattice coupling hybridizes those magnons with ordinary phonons, transferring the altermagnetic g-wave symmetry directly onto the phonon angular momentum across the entire Brillouin zone. First-principles calculations for the prototype CrSb map the resulting magnon-polarons, the avoided crossings, and the finite Berry curvatures that generate anomalous spin and phonon-angular-momentum Nernst responses without any applied field. The result positions bulk altermagnets as a materials platform for zero-field spin caloritronics and chiral phononics.","feed_headline":"Zero-field chiral phonons appear in altermagnets","feed_subtitle":"Magnon-phonon hybridization imprints g-wave angular momentum and drives anomalous Nernst effects in CrSb","key_machinery":"The first-order spin-lattice-coupling tensor (the displacement derivative of the exchange interactions) that generates the magnon-phonon vertices; after Holstein-Primakoff mapping and Colpa diagonalization these vertices produce hybridized magnon-polarons whose phonon angular momentum and generalized Berry curvatures are evaluated across the full zone.","core_discovery":"In the altermagnet CrSb, relativistic spin-lattice coupling hybridizes the altermagnetic magnon branches with phonons, opening gaps of up to 1.1 meV and imprinting a g-wave phonon angular momentum texture that reverses sign between adjacent 60-degree sectors of the Brillouin zone. The hybridized magnon-polarons therefore carry finite helicity (chiral phonons) at zero field and possess Berry curvatures that produce anomalous spin Nernst and phonon-angular-momentum Nernst coefficients, all while the net magnetization and the total equilibrium angular momentum remain zero.","pith_inferences":["Nonlinear thermal transport could resolve the g-wave angular pattern that linear-response currents average to period-pi.","The same hybridization mechanism should operate in other g-wave or d-wave altermagnets and may be tunable by strain or light doping.","Momentum-resolved circular dichroism or torque magnetometry on CrSb could directly map the predicted sector-dependent phonon helicity."],"forward_implications":["Bulk altermagnets can generate chiral phonons without net magnetization, external fields, or structural chirality.","Zero-field anomalous spin Nernst and phonon-angular-momentum Nernst transport become available in compensated collinear magnets.","The phonon angular momentum distribution itself becomes a phononic analogue of altermagnetism: g-wave anisotropy with exact global cancellation.","These materials are therefore candidates for zero-field spin-caloritronic and chiral-phononic devices."],"fun_headline_variants":["Chiral phonons emerge zero-field in altermagnets via magnon-phonon coupling","Magnon-phonon coupling imprints g-wave angular momentum on CrSb phonons","Hybrid magnon-polarons yield zero-field chiral phonons in altermagnets","Altermagnetic g-wave symmetry enforces chiral lattice dynamics without fields","Anomalous Nernst from hybridised magnon-polarons in zero-field CrSb"],"cache_read_input_tokens":128,"weakest_assumption_plain":"A first-order Taylor expansion of the magnetic exchange with respect to atomic displacements, together with the harmonic-phonon and linear Holstein-Primakoff approximations, is assumed to capture all of the hybridization, angular momentum, and Berry curvature.","fun_headline_variants_meta":{"raw":{"variants":["Chiral phonons emerge zero-field in altermagnets via magnon-phonon coupling","Magnon-phonon coupling imprints g-wave angular momentum on CrSb phonons","Hybrid magnon-polarons yield zero-field chiral phonons in altermagnets","Altermagnetic g-wave symmetry enforces chiral lattice dynamics without fields","Anomalous Nernst from hybridised magnon-polarons in zero-field CrSb"]},"model":"grok-4.5","effort":"low","cost_usd":0.004732,"raw_usage":{"total_tokens":1368,"prompt_tokens":773,"num_sources_used":0,"completion_tokens":98,"cost_in_usd_ticks":47320000,"prompt_tokens_details":{"text_tokens":773,"audio_tokens":0,"image_tokens":0,"cached_tokens":256},"completion_tokens_details":{"audio_tokens":0,"reasoning_tokens":497,"accepted_prediction_tokens":0,"rejected_prediction_tokens":0}},"tokens_in":773,"tokens_out":98,"duration_ms":5085,"temperature":1.0,"reasoning_tokens":497,"cache_read_input_tokens":256,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-07-10T21:13:32.385334+00:00","model_set":{"reader":"grok-4.5"},"falsifier":"Momentum-resolved measurements (Raman, X-ray, or inelastic neutron scattering) of phonon helicity in zero-field CrSb that fail to show the predicted g-wave sign reversals between the Gamma-L and Gamma-L-prime paths, or the absence of the calculated anomalous Nernst coefficients above ~100 K, would refute the central claim.","supporting_citations":[],"review_version":1}