{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"138a6fa877d782da586362b270a5f3ec03fb7a2b90a6bed707e48fe2a73b2c5b","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":["ai:gpt-5.5"],"kind":"seed"},"parents":["17e2ac3c6f82b5d11f06e0b22b7195d4110dab64c3c9f3eba623838791e0a04a","ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b"],"salt":"32de33a391735132a3e402d31798eb5ea39144573b571e7df0c8b8fb42b137c1","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"mechanism","assisted_by":["ai:gpt-5.5"],"external_id":"cm.mit-2d-electrons.metallic-origin","kind":"phenomenon","literature_status":"contested","n":"2","parents":[],"plain":"In clean silicon devices with few electrons, resistance falls by up to about ten times on cooling below a few kelvin, the opposite of what weak-disorder theory predicts. Which physical process causes this drop is disputed.","posed_since":"1994","precise":"In Si-MOSFETs, Si/SiGe and p-GaAs two-dimensional systems at $r_s \\sim 10-40$ ($r_s$ = mean interparticle spacing in units of the effective Bohr radius), $\\rho(T)$ on the metallic side falls by up to an order of magnitude for $T$ below roughly $0.1-0.3\\,E_F$, and an in-plane field that polarizes the spins suppresses the drop. Identify the mechanism among temperature-dependent screening of charged impurities, ballistic interaction corrections (Zala, Narozhny and Aleiner), the two-parameter renormalization group of the disordered Fermi liquid (Finkelstein; Punnoose and Finkelstein), and Pomeranchuk-type physics of a Wigner-crystal and liquid mixture (Spivak and Kivelson). An answer is one framework that fits $\\rho(T,n,B_{\\mathrm{parallel}})$ quantitatively across materials with independently measured parameters.","problem_ref":"17e2ac3c6f82b5d11f06e0b22b7195d4110dab64c3c9f3eba623838791e0a04a","references":"","settled_by":"A quantitative fit of $\\rho(T, n, B_{\\mathrm{parallel}})$ in several materials, with impurity density and Fermi-liquid parameters fixed by independent measurements, that excludes the competing mechanisms.","status_note":"Groups still disagree on whether screening theory accounts for the data; a 2021 review of ultra-clean Si systems argues for interaction-driven physics (arXiv 2102.00114).","title":"What causes the metallic resistance drop in dilute 2D electron 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