Superconductivity on the brink of spin-charge order in doped honeycomb bilayer

TL;DR

This paper uses a renormalization group approach to show how doping a bilayer honeycomb lattice can suppress excitonic order and induce unconventional superconductivity, revealing a new mechanism near spin-charge ordered states.

Contribution

It demonstrates the emergence of unconventional superconductivity from excitonic states in doped bilayer honeycomb systems using a controlled RG analysis.

Findings

Superconductivity appears after excitonic order is suppressed by doping.

Unconventional pairing mechanisms are favored near spin-charge ordered states.

The system transitions from excitonic order to a Fermi liquid as doping increases.

Abstract

Using a controlled weak-coupling renormalization group approach, we establish the mechanism of unconventional superconductivity in the vicinity of spin or charge ordered excitonic states for the case of electrons on the Bernal stacked bilayer honeycomb lattice. With one electron per site this system exhibits nearly parabolically touching conduction and valence bands. Such a state is unstable towards a spontaneous symmetry breaking, and repulsive interactions favor excitonic order, such as a charge nematic and/or a layer antiferromagnet. We find that upon adding charge carriers to the system, the excitonic order is suppressed, and unconventional superconductivity appears in its place, before it is replaced by a Fermi liquid. We focus on firmly establishing this phenomenon using the RG formalism within an idealized model with parabolic touching.