{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"1e05bedf11dcd525b7dc8dca8defa3da92ecb4e78b06ac5045dac92b328a0ee2","created":"2026-10-03T07:17:59Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["1f601410322cdcfe00cccad7c945bff94b200a5feac304a2341ddec819eedea6","5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"dc6bc3c338e1d21a67eea696a778a668e1c0b260c820978d5492630e1968d38b","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"yes-no","assisted_by":[],"external_id":"cm.heavy-fermions.ybrh2si2-fermi-jump","kind":"well-posed","literature_status":"contested","n":"1","parents":[{"note":"","parent_revision":"1f601410322cdcfe00cccad7c945bff94b200a5feac304a2341ddec819eedea6","relation":"special_case"}],"plain":"Hall-effect data suggest that the number of electrons in the Fermi sea of YbRh2Si2 changes abruptly at a critical magnetic field when cooled to zero temperature.","posed_since":"2004","precise":"In YbRh2Si2 at $T \\to 0$ across the critical field $B_c \\sim 600\\,\\mathrm{G}$ (field in the ab plane), determine whether the Fermi volume changes discontinuously from large (including the 4f hole) to small, as inferred from the Hall crossover whose width scales with $T$. An answer is a $T = 0$ extrapolation of the crossover width of Fermi-volume-sensitive transport (Hall coefficient, thermopower) in crystals with residual resistivity ratio of order 100 or more, or a Fermi-surface measurement at fields close to $B_c$, for example on chemically substituted samples whose critical field lies in the range accessible to quantum oscillations.","problem_ref":null,"references":"","settled_by":"Hall and thermopower crossover widths measured below 10 mK on the cleanest crystals and extrapolated to $T = 0$, together with Fermi-surface data on substituted samples whose critical field is high enough for quantum oscillations.","status_note":"ARPES (2015) found a large Fermi surface at zero field down to about 1 K, well above the crossover temperatures; no direct Fermi-surface measurement at $B_{\\mathrm{c}}$ exists.","title":"Does the Fermi volume of YbRh2Si2 jump at its critical 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