Emergence of Chiral Phonons in Two-Dimensional Kagome Lattices Harboring Electronic Chirality

Chiral phonons have recently been established to emerge in systems containing intrinsically chiral atomic structures or magnetic systems. Here we show that such intriguing chiral phonons can also be induced in nonmagnetic Kagome lattices that lack atomic structural chirality but harbor electronic chirality rooted in the presence of loop current order. This central finding is demonstrated using two types of loop current order, the restricted chiral flux phase characterized by a pure imaginary charge bond order and the more generalized chiral flux phase characterized by a complex charge bond order, as typified in layered AV_{3}Sb_{5} (A=Cs, Rb, K). At a mechanistic level, the time-reversal symmetry breaking caused by the electronic chirality is shown to pronouncedly influence their vibrational properties through electron-phonon coupling. The electronic chirality in either chiral flux phase is accompanied by a nonzero molecular Berry curvature, which in turn manifests as a nonlocal effective magnetic field of vectorial nature acting on the phonons. Consequently, the double degeneracy at each Brillouin zone corner is lifted, empowering chirality to the phonon modes. This Letter provides an indispensable component toward a more complete understanding of various chiral collective electronic phenomena in such structurally achiral systems.