Does magic-angle superconductivity require the neighbouring correlated insulator?

Saito et al. (Nature Physics 16, 926, 2020, arXiv:1911.13302) and Stepanov et al. (Nature 583, 2020, doi:10.1038/s41586-020-2459-6) found superconductivity in twisted bilayer graphene without correlated insulators at $\nu = \pm2$, for twist angles detuned from 1.1 deg or with metallic gates a few nm away. Determine whether the superconductor and the correlated insulator share an origin (pairing from doping the ordered insulator) or compete for the same flat-band electrons. An answer is the dependence of $T_{c}$ and of the insulating gap on gate-screening length $d$ and twist angle, with the pairing state shown to be the same or different with and without the insulator.

$T_c$, insulating-gap and gap-symmetry measurements in devices with gate distance $d$ varied from about 1 to 50 nm at fixed twist angle and strain.