Superconductivity and spin density wave in AA stacked bilayer graphene

TL;DR

This paper theoretically investigates electronic ordering in AA-stacked bilayer graphene, revealing how Coulomb interactions induce spin-density waves and potentially superconductivity, with the latter likely requiring phonon mediation for observable critical temperatures.

Contribution

It provides a detailed theoretical analysis of Coulomb interaction effects, including screening, on electronic phases in AA-stacked bilayer graphene, highlighting the conditions for spin-density wave and superconducting states.

Findings

Coulomb repulsion stabilizes spin-density wave at zero doping.

Superconductivity can emerge from inter-layer Coulomb interactions, but with very low critical temperature.

Strong intra-layer repulsion suppresses certain electron pairing mechanisms.

Abstract

This work theoretically analyzes electronic ordering in AA-stacked bilayer graphene and the role of the Coulomb interaction in these many-body phenomena. Using the random phase approximation to account for screening, we find intra-layer effective interactions to be much stronger than inter-layer interactions; under certain circumstances, the latter may also become attractive. At zero doping, the Coulomb repulsion stabilizes the spin-density wave state, with a N{\'e}el temperature in the tens of Kelvin. While dominant in the undoped system, the spin-density wave is destroyed by sufficiently strong doping and a superconducting phase emerges. We find that the effective Coulomb inter-layer interaction can give rise to superconductivity. However, the corresponding critical temperature is negligibly small, and phonon-mediated attraction must be introduced to observe it. Strong intra-layer repulsion suppresses order parameters that couple two intra-layer electrons. We point out a possible superconducting state with finite Cooper pair momentum.