Acoustic-phonon-mediated superconductivity in moir\'eless graphene multilayers

TL;DR

This paper explores how acoustic phonons can induce superconductivity in various graphene multilayers, explaining recent experiments and predicting new superconducting states, with a focus on electron-phonon interactions and Coulomb effects.

Contribution

It provides a comprehensive theoretical framework for phonon-mediated superconductivity in moiré-free graphene multilayers, incorporating realistic band structures and Coulomb interactions.

Findings

Superconductivity is predicted in ABCA tetralayer graphene due to electron-phonon interactions.

Superconductivity persists over a wide doping range in rhombohedral trilayer graphene.

Superconductivity in Bernal bilayer graphene occurs only near Van Hove singularities.

Abstract

We investigate the competition between acoustic-phonon-mediated superconductivity and the long-range Coulomb interaction in moir\'eless graphene multilayers, specifically, Bernal bilayer graphene, rhombohedral trilayer graphene, and ABCA-stacked tetralayer graphene. In these graphene multilayers, the acoustic phonons can realize, through electron-phonon coupling, both spin-singlet and spin-triplet pairings, and the intra-sublattice pairings ($s$-wave spin-singlet and $f$-wave spin-triplet) are the dominant channels. Our theory naturally explains the distinct recent experimental findings in Bernal bilayer graphene and rhombohedral trilayer graphene, and we further predict existence of superconductivity in ABCA tetralayer graphene arising from electron-phonon interactions. In particular, we demonstrate that the acoustic-phonon-mediated superconductivity prevails over a wide range of doping in rhombohedral trilayer graphene and ABCA tetralayer graphene while superconductivity exists only in a narrow range of doping near the Van Hove singularity in Bernal bilayer graphene. Key features of our theory are the inclusion of realistic band structures with the appropriate Van Hove singularities and Coulomb repulsion effects (the so-called "$\mu^*$ effect") opposing the phonon-induced superconducting pairing. We also discuss how intervalley scatterings can suppress the spin-triplet spin-polarized superconductivity. Our work provides detailed prediction based on electron-acoustic-phonon-interaction-induced graphene superconductivity, which should be investigated in future experiments.