Coulomb interaction, phonons, and superconductivity in twisted bilayer graphene

TL;DR

This paper investigates how Coulomb interactions, phonons, and electron-hole excitations influence superconductivity in twisted bilayer graphene, highlighting the role of phonon-electron coupling and Umklapp processes in pairing.

Contribution

It provides a detailed analysis of the polarizability and Coulomb screening effects that facilitate superconductivity across various twist angles and fillings in twisted bilayer graphene.

Findings

Superconductivity is enabled by screened Coulomb interactions and phonon coupling.

Umklapp processes are crucial for Cooper pair formation.

Superconducting gap varies across Fermi surface pockets.

Abstract

The polarizability of twisted bilayer graphene, due to the combined effect of electron-hole pairs, plasmons, and acoustic phonons is analyzed. The screened Coulomb interaction allows for the for- mation of Cooper pairs and superconductivity in a significant range of twist angles and fillings. The tendency toward superconductivity is enhanced by the coupling between longitudinal phonons and electron-hole pairs. Scattering processes involving large momentum transfers, Umklapp processes, play a crucial role in the formation of Cooper pairs. The magnitude of the superconducting gap changes among the different pockets of the Fermi surface.