{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"ee9d6b28c3b9bd2e047e79444bbf737b3cfb0bd36b9d326ae65f554becceffb4","created":"2026-10-03T07:17:59Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"c98547008670571d73964c33c39da855e22de34dfbf53050a0ac06ef0687fd9c","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"value","assisted_by":[],"external_id":"cm.electron-hydro.dirac-fluid-viscosity","kind":"well-posed","literature_status":"partially-resolved","n":"1","parents":[],"plain":"When graphene has equal numbers of electrons and holes, its carriers form a nearly ideal relativistic fluid. Its viscosity has been estimated only indirectly, so how close it comes to a conjectured quantum lower limit is not settled.","posed_since":"","precise":"For monolayer graphene at charge neutrality with $50\\,\\mathrm{K} < T < 300\\,\\mathrm{K}$, determine the shear viscosity $\\eta$, the entropy density s, and $\\eta/s$ in units of $\\hbar/k_B$, to compare with the conjectured lower bound $1/(4\\pi)$ (Kovtun, Son, Starinets 2005) and with kinetic theory at the measured effective coupling. Answer: $\\eta/s(T)$ with uncertainty.","problem_ref":null,"references":"","settled_by":"Spatially resolved imaging of the neutrality-point flow profile in channels (e.g. nitrogen-vacancy magnetometry) combined with an independent entropy measurement.","status_note":"Majumdar et al. (Nature Physics 2025, doi:10.1038/s41567-025-02972-z) inferred $\\eta/s$ within a factor of four of $1/(4 \\pi)$ from combined electrical and thermal transport; a direct flow-profile measurement of $\\eta$ with independent $s$ is lacking.","title":"Shear viscosity of the graphene Dirac fluid near charge neutrality","topic_ref":"3cd00f4643bbd06a95d69c9293583beea1b45782ba2be8604a26a1fe1e9a3620"},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"0c92cb4b4e3850ab63a97fbbf3275f78cad1f2082e0aee852f02d9e074213aa8","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"8cb2a9747ffb924f201becb23a09b02bd3f60e403804196d7154bf889e8216a0","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"nOYldMFgSz4y5puAxpjInC9O_LRhulHNN7R9pn1FPIbmB0uL6G9byuEhKqI6P7z3S4ChBUXvDb0CFV7ZGbXvBg"},"schema":"pubphys.envelope/1"},"record_hash":"0c92cb4b4e3850ab63a97fbbf3275f78cad1f2082e0aee852f02d9e074213aa8","leaf_index":968}