Is the low-density insulator in silicon devices a pinned Wigner solid?
In plain words
Below the critical density, clean silicon electron sheets stop conducting, and their current-voltage curves look like those of a solid held in place by impurities that slides when pushed hard enough. Whether this insulator is a pinned electron crystal or a disordered glass of trapped electrons is unsettled.
Precise statement
In low-disorder Si-MOSFETs at densities below the 2D metal-insulator critical density $n_{\mathrm{c}}$, I-V characteristics show two threshold voltages and broadband noise, resembling depinning and sliding of a vortex lattice (Brussarski, Li, Kravchenko, Shashkin and Sarachik, Nature Communications 9, 3803, 2018). Determine whether the insulating state has crystalline or hexatic positional order pinned by disorder (Wigner solid) or is a glass of localized electrons with no positional order, and whether the threshold fields scale with n and T as collective-pinning theory of an elastic crystal predicts.
What would settle it
A probe of positional order in the same samples (a microwave pinning-mode resonance, as seen for quantum Hall Wigner crystals in GaAs, or local imaging), together with threshold scaling compared quantitatively with collective-pinning theory.
Status in the literature
Transport evidence for a sliding quantum electron solid was reported in 2018; direct evidence of positional order in Si devices is lacking.