We present a theory of superconductivity in twisted bilayer graphene in which attraction is generated between electrons on the same honeycomb sublattice when the system is close to a sublattice polarization instability. The resulting Cooper pairs are spin-polarized valley singlets. Because the sublattice polarizability is mainly contributed by interband fluctuations, superconductivity occurs over a wide range of filling fraction. It is suppressed by (i) applying a sublattice polarizing field (generated by an aligned BN substrate) or (ii) changing moiré band filling to favor valley polarization. The enhanced intrasublattice attraction close to sublattice polarization instability is analogous to enhanced like-spin attraction in liquid He3 near the melting curve and the enhanced valley-singlet repulsion close to valley-polarization instabilities is analogous to enhanced spin-singlet repulsion in metals that are close to a ferromagnetic instability. We comment on the relationship between our pseudospin paramagnon model and the rich phenomenology of superconductivity in twisted bilayer and multilayer graphene.
|Journal||Physical Review Letters|
|State||Published - Oct 28 2022|
Bibliographical noteFunding Information:
We acknowledge informative conversations with Miguel Cazalilla, Tomasso Cea, Youngjoon Choi, Valentin Crépel, Liang Fu, Paco Guinea, Héctor Ochua, Andrea Young, and Haoxin Zhou. This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, under Award No. DE-SC0022106.
© 2022 American Physical Society.
ASJC Scopus subject areas
- Physics and Astronomy (all)