Kohn-Luttinger Superconductivity in Twisted Bilayer Graphene

Abstract

[EN] We show that the recently observed superconductivity in twisted bilayer graphene (TBG) can be explained as a consequence of the Kohn-Luttinger (KL) instability which leads to an effective attraction between electrons with originally repulsiveinteraction. Usually, the KL instability takes place at extremely low energy scales, but in TBG, a doubling and subsequent strong coupling of the van Hove singularities (vHS)intheelectronicspectrumoccursasthemagicangleisapproached,leadingtoextendedsaddlepoints in the highest valence band with almost perfect nesting between states belonging to different valleys. The highly anisotropic screening induces an effective attraction in a p-wave channel with odd parity under the exchange of the two disjoined patches of the Fermi line. We also predict the appearance of a spin-density waveinstability,adjacenttothesuperconductingphase,andtheopeningofagapintheelectronicspectrum from the condensation of spins with wave vector corresponding to the nesting vector close to the vHS.