Light-induced metastable mirror-symmetry breaking order in 1T-TiSe₂

Disentangling intertwined orders in correlated materials is often challenging because of the strong coupling and competition among multiple order parameters. Of particular interest is 1T-TiSe₂, a prototypical transition-metal dichalcogenide that hosts a 2×2×2 charge density wave (CDW) phase that has also been proposed to exhibit chirality, though its microscopic origin and even its existence remain under debate. Here, we demonstrate light-induced mirror-symmetry breaking order in TiSe₂ using time- and angle-resolved photoemission spectroscopy (tr-ARPES) with circularly polarized mid-infrared (mid-IR) pulses. Circularly polarized light imprints a long-lived metastable state that breaks mirror symmetry and persists for over 50 ps above the CDW transition temperature. By exploiting pump and probe helicities, we isolate the mirror-symmetry-breaking response and reveal that it suppresses CDW fluctuations, demonstrating that the two orders are distinct yet competing. These results establish optical imprinting of symmetry as a powerful route to disentangle intertwined orders in correlated quantum materials.