Chiral phonons induced by adsorption on graphene

The field of chiral phonons has developed rapidly in recent years, and two-dimensional materials provide an ideal platform for such research. However, as a pioneer of two-dimensional materials, chiral phonons in the graphene system have not been studied because the combined $\mathcal{PT}$ symmetry suppresses the existence of chiral phonons. In this work, we induce chiral phonons by adsorbing atoms on graphene. These chiral phonons can have quantized pseudoangular momentum at high-symmetry points $K$ and ${K}^{\ensuremath{'}}$. In addition to phonon chirality, adsorption can also induce nonzero phonon Berry curvature. Under a temperature gradient, the nonequilibrium phonon distribution can produce a total phonon angular momentum and nonlinear phonon Hall current in adsorbed graphene. Moreover, phonon chirality folding in graphene can be achieved through a specific adsorption way, which provides advantages for its Raman detection. Our work reveals the chiral phonon effect induced by adsorption in graphene, paving the way for further exploration of its chiral phonon physics.