Competing Nematic, Anti-ferromagnetic and Spin-flux orders in the Ground State of Bilayer Graphene

TL;DR

This paper investigates the phase diagram of bilayer graphene at zero temperature, identifying dominant nematic, antiferromagnetic, and spin-flux orders through a weak coupling renormalization group analysis.

Contribution

It systematically explores the initial coupling conditions leading to various symmetry-breaking phases in bilayer graphene, including the three main states and potential superconducting phases.

Findings

Nematic, antiferromagnetic, and spin-flux states dominate the phase diagram.

Weak coupling RG equations classify possible symmetry-breaking phases.

Additional ferroelectric and superconducting phases appear at the limits of weak coupling.

Abstract

We analyze the phase diagram of the Bilayer graphene (BLG) at zero temperature and doping. Assuming that at the high energies the electronic system of BLG can be described within a weak coupling theory (consistent with the experimental evidence), we systematically study the evolution of the couplings with going from high to low energies. The divergences of the couplings at some energies indicates the tendency towards certain symmetry breakings. Carrying out this program, we found that the phase diagram is determined by microscopic couplings defined on the short distances (initial conditions). We explored all plausible space of these initial conditions and found that the three states have the largest phase volume of the initial couplings: nematic, antiferromagnetic and spin flux (a.k.a quantum spin Hall). In addition, ferroelectric and two superconducting phases and appear only near the very limits of the applicability of the weak coupling approach. The paper also contains the derivation and analysis of the renormalization group equations and the group theory classification of all the possible phases which might arise from the symmetry breakings of the lattice, spin rotation, and gauge symmetries of graphene.