{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"e3d79c19504a1fb523a2098861d220a1981134ed8a8346b5162979d5448bec27","created":"2026-10-03T07:18:01Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"ecaf3eea9ea7174fe08f2e2e0ea6c6acb0084c03c4aa8763f522b36ae0d28790","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"yes-no","assisted_by":[],"external_id":"cm.weyl-semimetals.axion-cdw","kind":"well-posed","literature_status":"contested","n":"1","parents":[],"plain":"When a charge-density wave (a periodic ripple in electron density) gaps out the Weyl points of (TaSe4)2I, its sliding motion should act like the hypothetical axion particle; one experiment reported this and later work questioned it.","posed_since":"2019","precise":"Gooth et al. (Nature 575, 315, 2019, doi:10.1038/s41586-019-1630-4) reported a positive magnetoconductance of the sliding charge-density wave in (TaSe4)2I for E parallel to B, attributed to the phason (sliding mode) acting as a dynamical axion field $\\theta(r,t)$ coupled to E.B; Sinchenko et al. (Applied Physics Letters, 2022, doi:10.1063/5.0080380) questioned this interpretation. Determine whether the charge-density-wave phase is an axion insulator with dynamical $\\theta$: the test is a phason-carried response proportional to E.B, absent for E perpendicular to B, with magnitude set by the number of Weyl-node pairs. An answer is yes or no with that quantitative comparison.","problem_ref":null,"references":"","settled_by":"Angle-resolved nonlinear transport of the sliding mode with independent control of E and B on several samples, plus spectroscopic measurement of the phason mass and its coupling to light.","status_note":"Questioned in 2022; a 2023 Nature Materials study (Kim et al., doi:10.1038/s41563-023-01504-5) observed a massive phason in (TaSe4)2I, consistent with but not proof of axion dynamics.","title":"Is the charge-density wave in (TaSe4)2I an axion 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