Phonon-Induced Geometric\nChirality

Chiral properties have seen increasing use in recent\nyears, leading\nto the emerging fields of chiral quantum optics, plasmonics, and phononics.\nWhile these fields have achieved manipulation of the chirality of\nlight and lattice vibrations, controlling the chirality of materials\non demand has yet remained elusive. Here, we demonstrate that linearly\npolarized phonons can be used to induce geometric chirality in achiral\ncrystals when excited with an ultrashort laser pulse. We show that\nnonlinear phonon coupling quasistatically displaces the crystal structure\nalong phonon modes that reduce the symmetry of the lattice to that\nof a chiral point group corresponding to a chiral crystal. By reorienting\nthe polarization of the laser pulse, the two enantiomers can be induced\nselectively. Therefore, <i>geometric chiral phonons</i> enable\nthe light-induced creation of chiral crystal structures and therefore\nthe engineering of chiral electronic states and optical properties.