Topological phase transition to a hidden charge density wave liquid

Charge density waves (CDWs), electronic crystals that form within a hostsolid, have long been speculated to melt into a spatially textured electronic liquid.Though they have not been previously detected, liquid CDWs may nonetheless befundamental to the phase diagrams of many correlated electron systems, includinghigh temperature superconductors and quantum Hall states. In 1𝑻-TaS2, a leadingcandidate material, access to the liquid state is obstructed by a structural phasetransition. Using femtosecond light pulses, we bypass this transition to uncoverhidden CDW correlations via ultrafast electron diffraction. Upon photoexcitation,the CDW diffraction peaks broaden azimuthally, initially revealing a hexatic state.At higher temperatures, photoexcitation completely destroys translational andorientational order producing a diffuse ring at the CDW wavevector—a hallmarkof a liquid CDW. Our work provides compelling evidence for a spatially modulatedelectronic liquid and establishes a pathway for accessing hidden quantum phases.