{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"01a198b8ed5d1f8d8c9da9c38f7b10db5e9e84a5f16407c681eda0e2b88900a7","created":"2026-10-03T07:18:00Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"dec2194b94e5b4a3b5e44c4a6e411f754d43fc53e4d7067df5a6219dd063587b","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"yes-no","assisted_by":[],"external_id":"cm.mit-2d-electrons.mass-divergence","kind":"well-posed","literature_status":"contested","n":"1","parents":[],"plain":"Near the transition, electrons in silicon devices behave as if they become many times heavier. Whether this effective mass (the mass that sets how electrons respond to forces) truly diverges at a critical density, and whether that density coincides with the transition, is unsettled.","posed_since":"","precise":"In low-disorder (100) Si-MOSFETs ($n_{\\mathrm{c}} \\sim 1e11\\ \\mathrm{cm}^{-2}$) and Si/SiGe quantum wells, determine whether m*(n), obtained from thermodynamic magnetization (d mu/d B) and from quantum oscillations, diverges as m*/m_b ~ (n - $n_m$)^(-alpha) at a finite density n_m; whether n_m equals $n_{\\mathrm{c}}$ within error; and whether the spin susceptibility g* m* diverges at the same density (flat-band versus Stoner-type instability).","problem_ref":null,"references":"","settled_by":"Independent thermodynamic and quantum-oscillation measurements of $m*$ in samples of different disorder, showing whether $n_m$ is disorder independent and equal to $n_c$.","status_note":"Shashkin, Kravchenko and coworkers report a strong mass enhancement tending to diverge near $n_{c}$ in Si systems (2000s to 2021); independent confirmation of a true divergence is lacking.","title":"Does the effective mass diverge at the 2D metal-insulator 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