Why does graphene behave as a weakly interacting system?

TL;DR

This paper investigates why graphene exhibits weakly interacting behavior despite strong electron-electron interactions, demonstrating that RPA provides a rapidly converging, predictive framework for its many-body properties.

Contribution

The study calculates Coulomb interaction effects on graphene's quasiparticles at next-to-leading order in RPA, showing rapid convergence and predictive power across coupling strengths.

Findings

RPA corrections are small, indicating rapid convergence.

The quasiparticle residue and Fermi velocity are accurately described.

RPA remains valid even at strong coupling regimes.

Abstract

We address the puzzling weak-coupling perturbative behavior of graphene interaction effects as manifested experimentally, in spite of the effective fine structure constant being large, by calculating the effect of Coulomb interactions on the quasiparticle properties to next-to-leading order in the random phase approximation (RPA). The focus of our work is graphene suspended in vacuum, where electron-electron interactions are strong and the system is manifestly in a nonperturbative regime. We report results for the quasiparticle residue and the Fermi velocity renormalization at low carrier density. The smallness of the next-to-leading order corrections that we obtain demonstrates that the RPA theory converges rapidly and thus, in contrast to the usual perturbative expansion in the bare coupling constant, constitutes a quantitatively predictive theory of graphene many-body physics for any coupling strength.