Observation of a hidden charge density wave liquid

Charge density waves (CDWs), electronic crystals that form within a host solid, have long been theorized to melt into a spatially textured electronic liquid. Although such liquid CDWs have not been previously observed, they may be central to the phase diagrams of correlated electron systems, including high temperature superconductors and quantum Hall states. In 1T-TaS2, a promising material for hosting a liquid CDW, a structural phase transition hinders observation. Here, we use femtosecond light pulses to bypass this transition, revealing how topological defect dynamics govern hidden CDW correlations. Following photoexcitation, CDW diffraction peaks broaden azimuthally, indicating the emergence of a hexatic state. At elevated temperatures, photoexcitation fully destroys both translational and orientational order, leaving only a ring of diffuse scattering—a hallmark of a liquid CDW. These findings offer compelling evidence for a defect-unbinding transition to a CDW liquid. More broadly, this approach demonstrates a route to uncover electronic phases obscured by intervening transitions in thermal equilibrium.