Femtosecond time-resolved photoemission is used to investigate the time evolution of electronic
structure in the Mott insulator 1T-TaS2. A collapse of the electronic gap is observed within 100
femtoseconds after optical excitation. The photoemission spectra and the spectral function calculated by dynamical meanfield theory show that this insulator-metal transition is driven solely by
hot electrons. A coherently excited lattice displacement results in a periodic shift of the spectra
lasting for 20 ps without perturbing the insulating phase. This capability to disentangle electronic
and phononic excitations opens new directions to study electron correlation in solids.
The publication is available at link DOI: 10.1103/PhysRevLett.97.067402