Gate-Tunable Phonon Magnetic Moment in Bilayer Graphene

We develop a first-principles quantum scheme to calculate the phonon magnetic moment in solids. As a showcase example, we apply our method to study gated bilayer graphene, a material with strong covalent bonds. According to the classical theory based on the Born effective charge, the phonon magnetic moment in this system should vanish, yet our quantum mechanical calculations find significant phonon magnetic moments. Furthermore, the magnetic moment is highly tunable by changing the gate voltage. Our results firmly establish the necessity of the quantum mechanical treatment, and identify small-gap covalent materials as a promising platform for studying tunable phonon magnetic moment.

Automated summary

We have developed a first-principles quantum scheme to calculate the phonon magnetic moment in solids. By studying gated bilayer graphene, a material with strong covalent bonds, we have found significant and tunable phonon magnetic moments contrary to classical theory predictions. Our results emphasize the importance of quantum mechanical treatment and propose covalent materials with small-gap as promising platforms for investigating tunable phonon magnetic moment.