Nodal or fully gapped superconducting order in magic-angle graphene
In plain words
The energy needed to break an electron pair may vanish along certain directions (nodes) or stay finite everywhere, and which case holds narrows the possible pairing mechanisms.
Precise statement
Determine whether the superconducting gap of magic-angle twisted bilayer graphene near $\nu = -2 - \delta$ has nodes on the Fermi surface, and its irreducible representation under the $D_6$ point group ($D_3$ or lower with strain) combined with valley symmetry. Existing evidence is V-shaped tunnelling spectra and power-law superfluid stiffness $D_s(T)$ for $T << T_c$. An answer requires a phase-sensitive or momentum-resolved probe (Josephson interference, quasiparticle interference, or thermal conductivity $\kappa/T$ as $T \to 0$).
What would settle it
A phase-sensitive Josephson or quasiparticle-interference measurement identifying gap sign changes, consistent with low-temperature $\kappa/T$.
Status in the literature
Unverified note
2021 tunnelling spectra and 2025 microwave superfluid-stiffness measurements (Tanaka et al., Nature 2025) both suggest gap nodes; no phase-sensitive test as of 2026.