{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"c9d5a57d5f4c6df7012c2903e2232d70da733527c34f483798378a50307fc640","created":"2026-10-03T07:18:00Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"ebe59e6b91a1a75ea8492c75a5e578ea1b1d9b188767af399d452fb771fa382b","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"mechanism","assisted_by":[],"external_id":"cm.mit-2d-electrons.metallic-origin","kind":"phenomenon","literature_status":"contested","n":"1","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":null,"references":"","settled_by":"A quantitative fit of rho(T, n, B_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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