  Femtosecond time-resolved core-level photoemission spectroscopy with a
free-electron laser is used to measure the atomic-site specific charge-order
dynamics in the charge-density-wave/Mott insulator 1T-TaS2. After strong
photoexcitation, a prompt loss of charge order and subsequent fast
equilibration dynamics of the electron-lattice system are observed. On the time
scale of electron-phonon thermalization, about 1 ps, the system is driven
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 experiment opens the way to study the nonequilibrium dynamics of condensed
matter systems with full elemental, chemical, and atomic site selectivity.
