Ultrafast melting of a charge-density wave in the Mott insulator 1T-TaS2

Femtosecond time-resolved core-level photoemission spectroscopy with the free-electron laser FLASH as well as time- and angle-resolved photoemission spectroscopy with a higher-harmonics-generation source are used to measure the atomic-site and momentum specific charge-order dynamics of the charge-density wave in the Mott insulator 1T-TaS2. After strong photoexcitation, melting of the charge-density wave and the accompanying periodic lattice distortion is observed on two timescales. The subsequent fast electron-phonon thermalization drives the system across a phase transition from a long-range charge ordered state to a quasi-equilibrium state with domain-like short-range charge and lattice order. The combination of the two complementary sources opens the way to study the nonequilibrium dynamics of condensed matter systems with full momentum, elemental, chemical, and atomic-site selectivity.