{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"58fc3b842e656f1feb22f99adf3b27ec1cb011e243fc04134be295ee15d892de","created":"2026-10-03T07:17:56Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"1c58fba7b158451f802eee83412baea9554bd0b5c63f29b4e71b6b326dde6296","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"mechanism","assisted_by":[],"external_id":"beams.srf-cavities.anti-q-slope","kind":"phenomenon","literature_status":"contested","n":"1","parents":[],"plain":"When niobium is lightly doped with nitrogen, its energy loss falls as the field rises, the opposite of the usual behavior.","posed_since":"","precise":"N-doped Nb cavities show the temperature-dependent surface resistance $R_{\\mathrm{BCS}}$ decreasing with RF amplitude over $H_{\\mathrm{pk}} \\sim 100-900\\,\\mathrm{G}$, with a strong dependence on frequency and electron mean free path. Determine which mechanism (field-induced broadening of the quasiparticle density of states with a nonequilibrium quasiparticle distribution, reduced two-level-system losses, or other) reproduces $R_{\\mathrm{BCS}}(H, f, T, \\text{mean free path})$ quantitatively.","problem_ref":null,"references":"","settled_by":"A single model that fits $R_{\\mathrm{BCS}}(H, f, T)$ for cavities at three or more frequencies with independently measured mean free path and no per-cavity fit parameters.","status_note":"","title":"Origin of the anti-Q-slope in nitrogen-doped niobium","topic_ref":"e80fdf5b356ba02d4b3990f8abe874d0448c454195c990a76c551f83781fb3d8"},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"e76cc77c10d372ad4ec2ffe6c3b98ce6c9c4fc95e87ae1f41e4baa319e9d3499","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"7dbc49f83822798038960a330678d00960f1b3c6620bd078144d36e4bf06f956","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"FWJYi298wk9TeKSIeGKE2YlwOcT_jPOEv1dxHYWlhZQC1xe4QVJSS56SRzgzfRNCyerjNOvKOG9oBhKZ9KDVAQ"},"schema":"pubphys.envelope/1"},"record_hash":"e76cc77c10d372ad4ec2ffe6c3b98ce6c9c4fc95e87ae1f41e4baa319e9d3499","leaf_index":703}