Superconductivity from spin fluctuations and long-range interactions in magic-angle twisted bilayer graphene

TL;DR

This paper investigates how long-range electron interactions and spin fluctuations influence superconductivity in magic-angle twisted bilayer graphene, revealing that tuning these interactions can switch the system between magnetic and superconducting phases.

Contribution

It introduces a low-energy model capturing flat band shapes and demonstrates how long-range Coulomb interactions affect superconductivity in MATBG within the RPA framework.

Findings

Long-range interactions significantly impact the superconducting state.

Increasing long-range interactions can induce a transition from magnetic to superconducting phases.

Electron-electron interactions are crucial in controlling phases in MATBG.

Abstract

Magic-angle twisted bilayer graphene (MATBG) has been extensively explored both theoretically and experimentally as a suitable platform for a rich and tunable phase diagram that includes ferromagnetism, charge order, broken symmetries, and unconventional superconductivity. In this work, we investigate the intricate interplay between long-range electron-electron interactions, spin fluctuations, and superconductivity in MATBG. By employing a low-energy model for MATBG that captures the correct shape of the flat bands, we explore the effects of short- and long-range interactions on spin fluctuations and their impact on the superconducting (SC) pairing vertex in the Random Phase Approximation (RPA). We find that the SC state is notably influenced by the strength of long-range Coulomb interactions. Interestingly, our RPA calculations indicate that there is a regime where the system can traverse from a magnetic phase to the SC phase by \emph{increasing} the relative strength of long-range interactions compared to the on-site ones. These findings underscore the relevance of electron-electron interactions in shaping the intriguing properties of MATBG and offer a pathway for designing and controlling its SC phase.