What causes the metallic resistance drop in dilute 2D electron systems?
In plain words
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.
Precise statement
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.
What would settle it
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 in the literature
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).
Related problems
- More general than Why does an in-plane field suppress the 2D metallic state?