The Properties of Current Induced Chiral Phonons Recapitulate the Characteristics of the CISS Effect

Chiral phonons, with their intrinsic angular momentum, are potential contributors to the chiral induced spin selectivity (CISS) effect, which can induce significant spin polarization in the absence of strong spin-orbit coupling. An open question is how nonzero total phonon angular momentum may be generated. If chiral phonons are to underpin the observed CISS effect, they must have the symmetries observed in CISS experiments. That is, reversing the chirality or reversing the direction of the current flow through the active CISS structure should influence the phonon angular momentum in the same way that these sign reversals influence the CISS effect (i.e., reversing the current or inverting the structural chirality reverses the spin polarization). We use a tight-binding helical model to show how phonon angular momentum is generated from directional electric current flow and show that the phonons thus generated have the same symmetry properties as the CISS effect. We analyze the Berry potential of a nonadiabatically corrected Born-Oppenheimer Hamiltonian; the Berry potential originates in the current-carrying electronic states and acts as a pseudo vector potential that circularly polarizes phonons. We find that the chiral phonons produced by electrical currents have the symmetry characteristics of the CISS effect, suggesting that current-induced chiral phonons may plausibly provide a source that contributes to the CISS effect.