Chiral Phonons in Graphyne

TL;DR

This paper demonstrates the existence of chiral phonons in graphyne by breaking symmetries through selective doping, revealing their potential for tunable phononic devices and coupling with electronic properties.

Contribution

It introduces a method to induce chiral phonons in graphyne by symmetry breaking via atomic doping, a novel approach in phonon engineering.

Findings

Doping induces localized structural deformations in graphyne.

Chiral phonons arise from lifted phonon degeneracies due to doping.

Electron-rich dopants enhance phonon angular momentum and electron-phonon coupling.

Abstract

Chiral phonons, quantized lattice vibrations with circular polarization and non-zero angular momentum, offer new perspectives for phononic and quantum device engineering. Graphyne could be a promising candidate due to its unique lattice geometry, valley-structured electronic bands, and thermal transport capabilities. However, chiral phonons in graphyne remain unexplored owing to the existence of inversion ($\mathscr{P}$) and time-reversal ($\mathscr{T}$) symmetries. Herein, we have demonstrated the existence of chiral phonons in graphynes, achieved by breaking combined $\mathscr{PT}$ symmetry through atomic-selective substitutional doping. We find that the B, N, dopants and ortho BN co-dopant in 6-6-12 and $\gamma$-graphynes induce localized structural deformations. These deformations lift phonon degeneracies away from $\Gamma$ point and give rise to circularly polarized vibrational modes. We further established a strong correlation between chiral phonon angular momentum and electron affinity of dopants. Electron-rich dopants increase local electron density which could enable chiral phonon modes to couple more effectively with electronic environment. This in turn increases phonon angular momentum, indicating potential role of electron-phonon interactions in angular momentum modulation of chiral phonons. Our prosposed approach provides a tunable route for controlling chiral phonon behavior, paving way for development of advanced phononic devices.