Electrically tunable and reversible magnetoelectric coupling in strained bilayer graphene

TL;DR

This paper predicts a large, tunable magnetoelectric effect in strained bilayer graphene, where an applied electric field and strain induce a reversible orbital magnetization, with potential for experimental detection.

Contribution

It introduces a theoretical prediction of a significant, electrically tunable magnetoelectric coupling in strained bilayer graphene, highlighting its reversibility and experimental feasibility.

Findings

Orbital magnetization can reach ~5400 μ_B/μm^2 under 1% strain and bias.

Magnetoelectric susceptibility switches sign with electric field reversal.

Reversible effects are detectable via scanning magnetometry.

Abstract

The valleys in hexagonal two-dimensional systems with broken inversion symmetry carry an intrinsic orbital magnetic moment. Despite this, such systems possess zero net magnetization unless additional symmetries are broken, since the contributions from both valleys cancel. A nonzero net magnetization can be induced through applying both uniaxial strain to break the rotational symmetry of the lattice and an in-plane electric field to break time-reversal symmetry owing to the resulting current. This creates a magnetoelectric effect whose strength is characterized by a magnetoelectric susceptibility, which describes the induced magnetization per unit applied in-plane electric field. Here, we predict the strength of this magnetoelectric susceptibility for Bernal-stacked bilayer graphene as a function of the magnitude and direction of strain, the chemical potential, and the interlayer electric field. We estimate that an orbital magnetization of ~5400 $\mu_{\text{B}}/\mu\text{m}^2$ can be achieved for 1% uniaxial strain and a 10 $\mu\text{A}$ bias current, which is almost three orders of magnitude larger than previously probed experimentally in strained monolayer MoS$_2$. We also identify regimes in which the magnetoelectric susceptibility not only switches sign upon reversal of the interlayer electric field but also in response to small changes in the carrier density. Taking advantage of this reversibility, we further show that it is experimentally feasible to probe the effect using scanning magnetometry.