{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"f1c66374e6c8e473cf21a17d3d76b3931af8d7251dacd014e1e508cd70f9a9ff","created":"2026-10-03T07:17:57Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"c1928fb0f61a4da01948d4bd114f2312fa079dea31cd06d8c12f424550c6e57e","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"value","assisted_by":[],"external_id":"bio.friction-wear.superlubricity-scale","kind":"well-posed","literature_status":"open","n":"1","parents":[],"plain":"Two perfectly flat crystal surfaces whose atomic patterns do not match can slide almost without friction, an effect called structural superlubricity. It is unknown up to what contact area this survives before defects and elastic deformation bring friction back.","posed_since":"","precise":"For a single continuous incommensurate crystalline contact (graphite on graphite or on hexagonal boron nitride; not an ensemble of many small superlubric flakes), the friction force scales as $F \\sim A^\\gamma$ with contact area $A$ and $\\gamma < 1$ because of edges, defects and elastic deformation. Determine $\\gamma$ and the crossover length above which elastic pinning or defects restore a finite friction per unit area, and whether friction coefficients below $1e-3$ can persist for two-dimensional contacts with area above about $1e-4\\,\\mathrm{cm}^2$.","problem_ref":null,"references":"","settled_by":"Friction measurements on single-crystal incommensurate contacts of increasing area, compared with a theory of elastic pinning at incommensurate interfaces.","status_note":"Centimeter-long double-walled carbon nanotubes slide superlubrically (2013, a one-dimensional contact of small area), millimeter-scale superlubricity was reported in strained bilayer graphene (Androulidakis et al., Nat. Commun. 2020), and macroscale low friction has been obtained with many superlubric nanoflakes (2021-2024); a direct friction measurement on a single two-dimensional contact above about $1e-4\\ \\mathrm{cm}^{2}$ and the elastic-pinning crossover length are not established (2026).","title":"Up to what contact area does structural superlubricity survive","topic_ref":"dda1bf26b56de68ff6e0bc9fd1289af1a90b0889469abd062648a7c0948252d9"},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"9def8166f7ace98442bd065e24eea4f0ab186b24311fbbb483e8e3d0566b6ea1","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"4b05aa41944060d6b219d75c937b031ea4731a4a2af4fa2420d97d93f73e760c","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"LcOkRBe1uUY_szOPxDA_HPwI23onA4DnlvQyNtisC9MSJoVHJm2N_tO_qQVeGqciN2v5pJ6htpmq16PzBmBjBg"},"schema":"pubphys.envelope/1"},"record_hash":"9def8166f7ace98442bd065e24eea4f0ab186b24311fbbb483e8e3d0566b6ea1","leaf_index":775}