Light-Induced Ultrafast\nGlide-Mirror Symmetry Breaking\nin Black Phosphorus

Symmetry breaking plays an important role in the fields\nof physics,\nranging from particle physics to condensed matter physics. In solid-state\nmaterials, phase transitions are deeply linked to the underlying symmetry\nbreakings, resulting in a rich variety of emergent phases. Such symmetry\nbreakings are often induced by controlling the chemical composition\nand temperature or applying an electric field, strain, etc. In this\nwork, we demonstrate ultrafast glide-mirror symmetry breaking in black\nphosphorus through Floquet engineering. Upon near-resonance pumping,\na light-induced full gap opening is observed at the glide-mirror symmetry\nprotected nodal ring, suggesting light-induced breaking of the glide-mirror\nsymmetry. Moreover, the full gap is observed only in the presence\nof the light-field and disappears almost instantaneously (≪100\nfs) when the light-field is turned off, suggesting the ultrafast manipulation\nof the symmetry and its Floquet engineering origin. This work not\nonly demonstrates light–matter interaction as an effective\nway to realize ultrafast symmetry breaking in solid-state materials\nbut also moves forward toward the long-sought Floquet topological\nphases.