Routes to nodal pairing in moire systems

Despite years of theoretical and experimental work, the nature and mechanism of the superconducting states observed in TBG and its generalization to alternating-twist n-layer graphene have remained open questions. Recent experiments which measure tunneling conductance in alternating twist magic angle graphene have revealed indirect evidence for a nodal pairing in these systems [1,2]. In this work, we use a combination of numerical mean-field calculations at T=0 and analytical arguments to study the experimentally observed superconducting state near ν=2 in alternating twist magic angle graphene. We consider two types of interactions; one in which the superconducting state is stabilized by a more conventional electron-phonon interaction and one in which fluctuations of a nearby ordered state stabilizes superconductivity. Comparing the order parameter structure in the subspace of the flat bands and order parameter symmetries that result from these two approaches allows us to put constraints on options which leads to a nodal pairing in either scenario.

[1] M. Oh et al. Evidence for unconventional superconductivity in twisted bilayer graphene, Nature 600 (2021) 240-245

[2] Kim, H. et al. Spectroscopic Signatures of Strong Correlations and Unconventional Superconductivity in Twisted Trilayer Graphene. arXiv: 2109.12127