Symmetry of the superconducting order parameter in TBG and TTG

Determine the symmetry of the superconducting order parameter in magic-angle twisted bilayer graphene and magic-angle twisted trilayer graphene, seeking a sharp, model-independent identification of the pairing symmetry.

Background

The paper analyzes discrepancies between tunneling and Andreev STM measurements in moiré graphene superconductors and argues that the two distinct energy scales observed cannot be explained by a pseudogap versus superconducting gap dichotomy. Instead, the authors show that strong Fermi-velocity mismatch drives interfaces toward the tunneling regime and that Andreev bound states at a normal-superconductor interface in an unconventional superconductor can dominate the low-bias conductance.

Given the central role of an unconventional order parameter in their interpretation, the precise symmetry of the superconducting order parameter in twisted bilayer (TBG) and twisted trilayer (TTG) graphene is essential. The authors used a single-band d-wave model as an illustrative example but emphasize that definitively establishing the actual pairing symmetry in these materials remains unresolved and is independent of microscopic details. They note that Andreev spectroscopy is one of the few phase-sensitive probes available, highlighting the importance of modeling multi-band scenarios.