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

Shubhayu Chatterjee; Taige Wang; Erez Berg; Michael P. Zaletel

doi:10.1038/s41467-022-33561-w

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arXiv · 2109.00002

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

Shubhayu Chatterjee·Taige Wang·Erez Berg·Michael P. Zaletel

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Abstract

Superconductivity was recently discovered in rhombohedral trilayer graphene (RTG) in the absence of a moir\'e 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.

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Shubhayu Chatterjee, Taige Wang, Erez Berg, Michael P. Zaletel. 2021-08-31. Inter-valley coherent order and isospin fluctuation mediated superconductivity in rhombohedral trilayer graphene. https://doi.org/10.1038/s41467-022-33561-w

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