  Chiral properties have seen increasing use in recent years, leading to the
emerging fields of chiral quantum optics, plasmonics, and phononics. While
these fields have achieved manipulation of the chirality of light and lattice
vibrations, controlling the chirality of materials on demand has yet remained
elusive. Here, we demonstrate that linearly polarized phonons can be used to
induce geometric chirality in achiral crystals when excited with an ultrashort
laser pulse. We show that nonlinear phonon coupling quasistatically displaces
the crystal structure along phonon modes that reduce the symmetry of the
lattice to that of a chiral point group corresponding to a chiral crystal. By
reorienting the polarization of the laser pulse, the two enantiomers can be
induced selectively. Therefore, geometric chiral phonons enable the
light-induced creation of chiral crystal structures and offer a pathway to
engineering chiral electronic states and optical properties.
