What binds electron pairs in magic-angle graphene superconductors?

Twisted bilayer graphene at $\theta \sim 1.05-1.15\,\mathrm{deg}$ superconducts with $T_c$ up to $\sim 3\,\mathrm{K}$ near filling $\nu = -2 - \delta$ ($\nu$ = electrons per moire cell measured from charge neutrality). Determine the dominant pairing interaction (intervalley K-point optical phonons, other phonons, spin or valley fluctuations, Coulomb-driven Kohn-Luttinger pairing, or a combination) and the order-parameter symmetry. An answer is a microscopic model that reproduces the measured $T_c(\nu, \theta)$, tunnelling gap spectrum and superfluid stiffness without retuned parameters.

A phase-sensitive gap-symmetry measurement plus an isotope or phonon-engineering test, combined with a parameter-free calculation reproducing $T_{c}(\nu, \theta)$.