Anomalous superconductivity and unusual normal state properties of bilayer and twisted graphene (Brief review)

TL;DR

This review discusses the emergence of anomalous superconductivity and unusual normal state behaviors in bilayer and twisted graphene, highlighting the role of Kohn--Luttinger mechanisms, interplay with other orders, and recent experimental findings.

Contribution

It provides a comprehensive overview of theoretical and experimental insights into superconductivity and normal state anomalies in bilayer and twisted graphene systems.

Findings

Kohn--Luttinger superconductivity can occur in hexagonal lattice systems.

Interplay between superconductivity and spin density waves in various graphene bilayers.

Observation of nematic superconductivity and abnormal normal phase properties in twisted bilayer graphene.

Abstract

It has been shown that the Kohn--Luttinger superconductivity mechanism interplaying with other types of ordering can be implemented in systems with a hexagonal lattice. A number of unusual properties of such systems in the normal phase have also been considered. Our previous results on Kohn--Luttinger superconductivity with $p$-, $d$-, and $f$-wave pairing in monolayer and AB bilayer graphene, obtained disregarding the effect of substrate potential and impurities, have been presented in the first part. Then, the interplay of the superconducting Kohn--Luttinger state with the spin density wave state in actual AB, AA, and twisted bilayer graphene has been discussed in detail. In the last parts, a number of anomalous properties in the normal phase and the appearance of nematic superconductivity alongside with the spin density wave in the twisted bilayer graphene have been presented.