Ruderman-Kittel-Kasuya-Yosida interaction in biased bilayer graphene

TL;DR

This paper investigates the RKKY interaction in bilayer graphene, deriving analytical and numerical results that reveal how doping and gate voltage can tune magnetic interactions, with implications for spintronic applications.

Contribution

It provides analytical expressions for RKKY interaction in unbiased bilayer graphene and explores the effects of doping and gate voltage on its tunability, comparing two-band and four-band models.

Findings

RKKY interaction in unbiased BLG is bipartite and oscillatory.

Doping induces beating patterns in RKKY oscillations.

Gate voltage allows tuning of the RKKY interaction range and strength.

Abstract

We study the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between two contact magnetic impurities placed on bilayer graphene (BLG). We compute the interaction mediated by the carriers of the pristine and biased BLG as well as the conduction electrons of the doped system. The results are obtained from the linear-response expression for the susceptibility written in terms of the integral over lattice Green's functions. For the unbiased system, we obtain some analytical expressions in terms of the Meijer G-functions, which consist of the product of two oscillatory terms, one coming from the interference between the two Dirac points and the second coming from the Fermi momentum. In particular, for the undoped BLG, the system exhibits the RKKY interaction commensurate with its bipartite nature as expected from the particle-hole symmetry of the system. Furthermore, we explore a beating pattern of oscillations of the RKKY interaction in a highly doped BLG system within the four-band continuum model. Besides, we discuss the discrepancy between the short-range RKKY interaction calculated from the two-band model and that obtained from the four-band continuum model. The final results for the applied gate voltage are obtained numerically and are fitted with the functional forms based on the results for the unbiased case. In this case, we show that the long-range behavior is scaled with a momentum that depends on Fermi energy and gate voltage, allowing the possibility of tuning of the RKKY interaction by gate voltage.