Note on Angular Momentum of Phonons in Chiral Crystals

Phonon angular momentum in chiral materials has been widely studied in spintronics and condensed matter physics. In chiral crystals, this is not the conserved quantity in contrast to the pseudo-angular momentum. To highlight this point and to understand the behavior of the angular momentum, we reexamined phonon dispersion theory based on the irreducible representation of helix and found the distinction of these angular momentum is originated from chirality.