Electronic multicriticality in bilayer graphene

TL;DR

This paper analyzes the phase diagram of bilayer graphene at neutrality, revealing how various interactions and external fields influence the emergence of nematic and antiferromagnetic orders through an extended renormalization group approach.

Contribution

It extends previous RG analysis to include finite temperature, trigonal warping, and electric fields, providing a comprehensive map of possible ordered states in bilayer graphene.

Findings

Nematic order dominates when forward scattering is strong.

Layer antiferromagnet appears with increased back and layer imbalance scattering.

The phase diagram is rich and includes conditions for multiple ordered states.

Abstract

We map out the possible ordered states in bilayer graphene at the neutrality point by extending the previous renormalization group treatment of many-body instabilities to finite temperature, trigonal warping and externally applied perpendicular electric field. We were able to analytically determine all outcomes of the RG flow equations for the 9 four-fermion coupling constants. While the full phase diagram exhibits a rich structure, we confirm that when forward scattering dominates, the only ordering tendency with divergent susceptibility at finite temperature is the nematic. At finite temperature this result is stable with respect to small back and layer imbalance scattering; further increasing their strength leads to the layer antiferromagnet. We also determine conditions for other ordered states to appear and compare our results to the special cases of attractive and repulsive Hubbard models where exact results are available.