paper

Inter-valley coherent order and isospin fluctuation mediated superconductivity in rhombohedral trilayer graphene

arXiv:2109.00002 · doi:10.1038/s41467-022-33561-w

Abstract

Superconductivity was recently discovered in rhombohedral trilayer graphene (RTG) in the absence of a moiré potential. Superconductivity is observed proximate to a metallic state with reduced isospin symmetry, but it remains unknown whether this is a coincidence or a key ingredient for superconductivity. Using a Hartree-Fock analysis and constraints from experiments, we argue that the symmetry breaking is inter-valley coherent (IVC) in nature. We evaluate IVC fluctuations as a possible pairing glue, and find that they lead to chiral unconventional superconductivity when the fluctuations are strong. We further elucidate how the inter-valley Hund's coupling determines the spin-structure of the IVC ground state and breaks the degeneracy between spin-singlet and triplet superconductivity. Remarkably, if the normal state is spin-unpolarized, we find that a ferromagnetic Hund's coupling favors spin-singlet superconductivity, in agreement with experiments. Instead, if the normal state is spin-polarized, then IVC fluctuations lead to spin-triplet pairing.

arXiv comment8 + 22 pages, 3 + 5 figures; (v2) 8 + 24 pages, 3 + 6 figures, additional discussion of pairing symmetries; (v3) 9 + 25 pages, 3 + 7 figures, added phase diagram and correlation length estimate

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