Phonon-induced geometric chirality

Chiral phonons conventionally describe circularly polarized lattice vibrations that carry angular momentum and that represent a case of dynamic chirality. Here, we demonstrate that linearly polarized phonons can also induce geometric chirality in achiral crystals when excited nonlinearly with an ultrashort laser pulse. We show that nonlinear phonon coupling can be used to quasistatically displace the crystal structure along the eigenvectors of phonon modes that reduce the symmetry of the lattice to that of the enantiomorphic point groups characterizing chiral crystals. The structure can be switched between the two enantiomers by reorienting the polarization of the laser pulse. These linearly polarized chiral phonons enable the creation of chiral crystal geometries on demand and offer a novel pathway towards engineering chiral electronic states and optical properties