RKKY interaction in bilayer graphene

TL;DR

This paper investigates the RKKY interaction in bilayer graphene, revealing decay behaviors, magnetic coupling types, and anisotropic oscillations, with results bridging single-layer and bilayer graphene models.

Contribution

It provides a detailed analysis of RKKY interactions in bilayer graphene using a four-bands model, highlighting decay rates, magnetic nature, and oscillatory factors, extending understanding beyond previous two-bands approximations.

Findings

Intralayer RKKY interactions decay as 1/R^6 and 1/R^2 on same sublattice.

Interlayer RKKY interactions decay as 1/R^4 and 1/R^6 depending on sublattice configuration.

Interactions exhibit anisotropic oscillatory factors similar to single-layer graphene.

Abstract

We study the RKKY interaction between two magnetic impurities located on same layer (intralayer case) or on different layers (interlayer case) in undoped bilayer graphene in the four-bands model, by directly calculating the Green functions in the eigenvalues and eigenvectors representation. Our results show that both intra- and interlayer RKKY interactions between two magnetic impurities located on same (opposite) sublattice are always ferromagnetic (antiferromagnetic). Furthermore we find unusual long-distance decay of the RKKY interaction in BLG. The intralyer RKKY interactions between two magnetic impurities located on same sublattice, $J^{A_{n}A_{n}}(\mathbf{R})$ and $J^{B_{n}B_{n}}(\mathbf{R)}$, decay closely as $1/R^{6}$ and $1/R^{2}$ at large impurity distances respectively, but when they are located on opposite sublattices the RKKY interactions exhibit $1/R^{4}$ decays approximately. In the interlayer case, the RKKY interactions between two magnetic impurities located on same sublattice show a decay close to $1/R^{4}$ at large impurity distances, but if two magnetic impurities be on opposite sublattices the RKKY interactions, $J^{A_{1}B_{2}}(\mathbf{R})$ and $J^{B_{1}A_{2}}(\mathbf{R)}$, decay closely as $1/R^{6}$ and $1/R^{2}$ respectively. Both intra- and interlayer RKKY interactions have anisotropic oscillatory factors which for intralayer case is equal to that for single layer graphene. Our results at weak and strong interlayer coupling limits reduce to the RKKY interaction of SLG and that of BLG in the two-bands approximation respectively.