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arXiv · 1805.06449

Unconventional Superconductivity and Density Waves in Twisted Bilayer Graphene

Hiroki Isobe·Noah F. Q. Yuan·Liang Fu
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Abstract

We study electronic ordering instabilities of twisted bilayer graphene with $n=2$ electrons per supercell, where correlated insulator state and superconductivity are recently observed. Motivated by the Fermi surface nesting and the proximity to Van Hove singularity, we introduce a hot-spot model to study the effect of various electron interactions systematically. Using renormalization group method, we find $d$/$p$-wave superconductivity and charge/spin density wave emerge as the two types of leading instabilities driven by Coulomb repulsion. The density wave state has a gapped energy spectrum at $n=2$ and yields a single doubly-degenerate pocket upon doping to $n>2$. The intertwinement of density wave and superconductivity and the quasiparticle spectrum in the density wave state are consistent with experimental observations.

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Hiroki Isobe, Noah F. Q. Yuan, Liang Fu. 2018-05-16. Unconventional Superconductivity and Density Waves in Twisted Bilayer Graphene. https://doi.org/10.1103/physrevx.8.041041

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