Chatterjee Shubhayu, Wang Taige, Berg Erez, Zaletel Michael P
Department of Physics, University of California, Berkeley, CA, 94720, USA.
Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA.
Nat Commun. 2022 Oct 12;13(1):6013. doi: 10.1038/s41467-022-33561-w.
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.
最近在没有莫尔势的菱面体三层石墨烯（RTG）中发现了超导性。在等旋对称性降低的金属态附近观察到了超导性，但这究竟是巧合还是超导的关键因素仍不清楚。通过Hartree-Fock分析和实验约束，我们认为对称性破缺本质上是谷间相干（IVC）的。我们将IVC涨落评估为一种可能的配对胶水，并发现当涨落很强时，它们会导致手性非传统超导。我们进一步阐明了谷间洪德耦合如何决定IVC基态的自旋结构，并打破自旋单重态和三重态超导之间的简并。值得注意的是，如果正常态是自旋非极化的，我们发现铁磁洪德耦合有利于自旋单重态超导，这与实验结果一致。相反，如果正常态是自旋极化的，那么IVC涨落会导致自旋三重态配对。
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